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Effects of Fragrance on Emotions: Moods and Physiology

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Stephen Warrenburg, Effects of Fragrance on Emotions: Moods and Physiology, Chemical Senses , Volume 30, Issue suppl_1, January 2005, Pages i248–i249, https://doi.org/10.1093/chemse/bjh208

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Smelling a delightful aroma can be a very pleasurable experience, but can it be measured scientifically? Over the past 20 years International Flavors & Fragrances Inc. (IFF) has been working to refine its methods of measuring both the subjective and physiological effects of aromas and fragrances on emotions. We have developed a self-report method called Mood Mapping™ that reliably measures the mood associations of aromas, whether simple ingredients or finished fragrances in consumer products ( Warrenburg, 2002 ). Mood Mapping provides a choice of eight mood categories to panelists, who are asked to smell the aroma of a sample and ‘pick the mood category that best matches the aroma of the sample’. We found that this straightforward voting technique results in clearer and more reliable differentiation among aromas than do techniques that require respondents to rate each mood for each sample being evaluated. The resulting mood profiles of each aroma can be mapped by multidimensional scaling or principal component analysis. Figure 1 displays the voting results for clementine, a citrus aroma, versus vanilla. Both are equally pleasant, but the former is more stimulating and the latter more relaxing. The Mood Map reflects these differences by their positions in the Arousal ( Y ) dimension, yet also shows their hedonic similarity on the Positive/Negative ( X ) dimension. The other points are other aromas that evoke different patterns of the eight moods.

Measurement of moods in this way can be conducted in combination with consumer research of fragranced (or flavored) products. When these results are mapped we have found that the four positive moods identify the major dimensions of the map. Thus, positive consumer reactions tend to reflect the major mood dimensions of happiness, stimulation, relaxation and sensuality that underlie a wide variety of specific attributes identified as applying to such products. Furthermore, we have found that this is true in populations tested around the world. We have built a database for our creative staff, called the Consumer Fragrance Thesaurus, that catalogs the moods, attributes, colors and other qualities of fragrances tested in different areas of the world ( Warrenburg, 1999 ).

One of our principal interests has been to discover whether fragrance can be used as a stress-relief agent in a consumer product. Stress is a global affliction, a fact that is not only acknowledged anecdotally, but is documented by global consumer surveys ( Roper, 2003 ). Whether one resides in the developed or developing world, stress is a problem that reduces the quality of life for a large proportion of the world’s citizens as reported by the World Health Organization (2001 ). Furthermore, there is considerable evidence that stress can either directly or indirectly exacerbate a variety of illnesses and that the reduction of stress has both short- and long-term health benefits.

We were interested to learn whether the most relaxing fragrances in the Consumer Fragrance Thesaurus could be powerful enough to reduce laboratory-induced stress responses measured physiologically. To determine if fragrance can have a physiological effect, further tests were conducted on these subjectively ‘relaxing’ fragrances using psychophysiological methods (heart rate, blood pressure, skin resistance, muscle tension, etc.) to ascertain whether they are truly stress-reducing. We used a standard laboratory stressor, the Stroop test, in a series of studies of various relaxing fragrances identified by Mood Mapping. We obtained the electromyogram (EMG) from the trapezius muscle (back of the shoulder), which reliably shows an increase during the Stroop test. This measurement was utilized because shoulder and neck tension is universal and is an easily understood consumer measure of stress.

In the course of this testing, we discovered that certain relaxing fragrances are able to reduce stress-induced muscle tension as measured in the shoulder area. We found that a special type of relaxing fragrance, Myo-relax ® (patent pending), has a muscle relaxing effect: such fragrances significantly reduce the trapezius EMG stress response. These studies reveal that fragrance is indeed powerful enough to counteract stress in a performance task. This new fragrance technology is being applied to products requiring convincing evidence that a fragrance is physically relaxing, or de-stressing. Aromatherapy products represent a substantial and growing area of the marketplace and this type of research can strengthen the basis for making stress-relief claims in these products.

Figure 1 Mood Map results for clementine, a citrus aroma, versus vanilla.

Roper, A.S.W. ( 2003 ) When stress strikes, what can business do? Roper Reports Global Pulse , New York, May 2003.

Warrenburg, S. ( 1999 ) The Consumer Fragrance Thesaurus: putting consumer insights into the perfumer’s hands . Aroma-Chology Rev. , VIII, 4– 7.

Warrenburg, S. ( 2002 ) Measurement of emotion in olfactory research . In Given, P. and Paredes, D. (eds), Chemistry of Taste: Mechanisms, Behaviors, and Mimics. American Chemical Society, Washington, DC, pp. 243– 260.

World Health Organization ( 2001 ) The World Health Report: 2001. Mental Health: New Understanding, New Hope. World Health Organization, Geneva.

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• Review article
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• Published: 26 June 2021

The scent of attraction and the smell of success: crossmodal influences on person perception

• Charles Spence   ORCID: orcid.org/0000-0003-2111-072X 1  

Cognitive Research: Principles and Implications volume  6 , Article number:  46 ( 2021 ) Cite this article

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In recent decades, there has been an explosion of research into the crossmodal influence of olfactory cues on multisensory person perception. Numerous peer-reviewed studies have documented that a variety of olfactory stimuli, from ambient malodours through to fine fragrances, and even a range of chemosensory body odours can influence everything from a perceiver’s judgments of another person’s attractiveness, age, affect, health/disease status, and even elements of their personality. The crossmodal and multisensory contributions to such effects are reviewed and the limitations/peculiarities of the research that have been published to date are highlighted. At the same time, however, it is important to note that the presence of scent (and/or the absence of malodour) can also influence people’s (i.e., a perceiver’s) self-confidence which may, in turn, affect how attractive they appear to others. Several potential cognitive mechanisms have been put forward to try and explain such crossmodal/multisensory influences, and some of the neural substrates underpinning these effects have now been characterized. At the end of this narrative review, a number of the potential (and actual) applications for, and implications of, such crossmodal/multisensory phenomena involving olfaction are outlined briefly.

Significance statement

People have been wearing fragrance for millennia in the belief that masking their body odour will help them to look more attractive. Empirical studies of the crossmodal influence of ambient odours, personal fragrances, and chemosensory body-related odours on multisensory perception are, though, a much more recent phenomenon. A large body of research now shows that the presence of odour can indeed influence person perception through a range of mechanisms from mood-induction to crossmodal affective/semantic priming, and changes in arousal. Attractiveness judgments would appear to be influenced to a greater extent than other judgments about people by the presence of a pleasant (as compared to an unpleasant) scent. Establishing the most appropriate experimental methods by which to support claims around the efficacy of fragrance is of great commercial interest to the fragrance and home and personal care industries. At the same time, however, the methodological decisions in laboratory research designed to maximize the likelihood of observing a crossmodal effect on visual judgments of person perception often reduce the ecological-validity of the experimental designs. As such, the real-world relevance of much of the research that has demonstrated a crossmodal effect of olfactory cues (no matter whether person-related or ambient) on person perception can be questioned. This review critically evaluates the extensive literature on the olfactory modulation of person perception and highlights a number of the peculiar (or idiosyncratic) aspects of the underpinning experimental designs. At the same time, a number of specific suggestions for future research are also raised.

Introduction

The sensory cues that happen to be presented in one modality have often been shown to influence our perception of those stimuli presented in a different sensory modality (Spence, 2021a ). So, for example, the presence of pleasant versus unpleasant olfactory stimuli influence people’s ratings of everything from paintings to pictures (Wrzesniewski et al., 1999 ; see Spence, 2002 , 2020a , for reviews). Similarly, olfactory cues have also been demonstrated to influence various aspects of person perception, such as attractiveness (Demattè et al., 2007 ), gender (Zhou et al., 2014 ), and affect. At the same time, however, it turns out that an individual’s personal odour profile provides a surprisingly rich source of chemosensory information about various aspects of their health (or disease) status (Shirasu & Touhara, 2011 ), their ovulatory status (in the case of fertile women; Havlíček et al., 2006 ; Singh & Bronstad, 2001 ), as well as about certain aspects of their personality (e.g., Sorokowska et al., 2012 , 2016 ). For instance, according to Olsson et al. ( 2014 ), human body odour contains an early chemosensory cue of sickness (see also Moshkin et al., 2012 ). Meanwhile, different chemosensory signals have been associated with different emotions such as fear and anxiety (de Groot et al., 2012 ). A person’s body odour can also be influenced by aspects of their diet (Fialová et al., 2013 ; Havlicek & Lenochova, 2006 ), while single men have also been shown to have stronger body odour than partnered men, attributable to their higher levels of testosterone (Mahmut & Stevenson, 2019 ).

Even our choice of personal fragrance turns out not to be as random as it might first appear, and hence may also reveal more about us than one might realize (Allen et al., 2016 ; Janssens & De Pelsmacker, 2009 ; Martins et al., 2005 ; Milinski & Wedekind, 2001 ). And, one step further removed from the person themselves (and the fragrances that they choose to wear), ambient (mal)odours have sometimes been shown to influence our ratings of others too (Rotton, 1983 ). As such, while an individual’s olfactory signature, no matter whether natural or synthetic, presumably constitutes one component of multisensory person perception, the more general influence of synthetic ambient olfactory stimuli on person perception (as assessed visually) may better be considered to be a crossmodal phenomenon instead.

Given that olfactory cues have been shown to influence people’s visual judgments of everything from paintings to pictures and portraits (Banks et al., 2012 ; see Spence, 2020a , for a review), one might be tempted to wonder whether there is actually anything special about the crossmodal effects of olfaction that have been documented in terms of multisensory person perception? One difference that is immediately worth highlighting here relates to the fact that humans do have a biologically relevant natural aroma (even if they typically choose to hide it; Largey & Watson, 1972 ), Footnote 1 while paintings, pictures, photos, and portraits are essentially odourless (and, what is more, are not expected to smell; though see Braun et al., 2016 ). That said, they are also typically silent; and yet what we hear has been shown to affect our ratings of such unimodal visual stimuli (Gerdes et al., 2014 ). Given the widespread and longstanding suggestion that wearing fragrance can make us look more attractive to others, Footnote 2 one might therefore wonder why more works of art aren’t scented (e.g., at the National Portrait Gallery in London, for example). Would the Venus de Milo statue or the Mona Lisa painting be rated as any more beautiful were a matching fragrance to be been released in The Louvre galleries in Paris where the works are displayed? Note that this suggestion is not as far-fetched as perhaps it might seem, given that, in 2019, The Louvre commissioned a number of top perfumers to create fragrances for eight of the works in the collection (Bremner, 2019 ; Spence, 2020a ). Footnote 3

One area of particular interest concerns whether the multisensory/crossmodal influence of olfactory stimuli on face/person perception is specific, or whether instead much the same effects can potentially be documented by the presence of any other atmospheric cue, for example, the emotional affect, or arousal that is often elicited by listening to music, or the attractiveness of the environment in which the faces happen to be rated (Maslow & Mintz, 1956 ). Here, for example, there is research showing the crossmodal impact of emotional music on the perception of, and memory for, faces (Proverbio et al., 2015 ). Indeed, the arousal that can be induced by listening to music has been shown to influence our ratings of the attractiveness of faces (e.g., Marin et al., 2017 ; May & Hamilton, 1980 ; cf. Risso et al., 2021 , for the suggestion that olfactorily induced changes in arousal may also be one of the mechanisms by which scent may influence judgments of visual attractiveness). Given that ambient olfactory stimuli influence our mood (Herz, 2002 ; Schiffman, 1974 ; Spence, 2020c ; Vernet-Maury et al., 1999 ), such emotional crossmodal influences on stimulus processing are likely to be relatively nonspecific (Pourtois et al., 2013 ), meaning that they may affect our evaluation of many different kinds of perceptual stimuli (i.e., not just faces). At the same time, however, it is important to note that the presence of scent not only influences a perceiver’s impression of other people, it may also affect their impression of themselves, possibly enhancing their self-confidence (and, as we will see later, this may also be picked up by others too). At the same time, however, it is also important to differentiate the concept of crossmodal olfactory–visual interactions with olfactory influences on person perception, which although partly visual are also importantly social, emotional, and cultural (cf. Cerulo, 2018 ; Moeran, 2007 ).

Evaluating the evidence on fragrance effects on person perception, and the underlying cognitive mechanisms, where they are known, or have been suggested, may also help those wishing to critically evaluate the popular psychology literature that has developed around the suggestion that perfume can be used as an effective tactic of impression management in social and organizational settings (Baron, 1988 ; Levine & McBurney, 1986 ; Lobmaier et al., 2020 ; Newsweek, 1984 ; Zemke & Shoemaker, 2007 ), in non-verbal communication, and in order to engage in behavioural, or sensory, nudging (Baron, 1980 ; Cowley et al., 1977 ; De Lange et al., 2012 ; Ebster & Kirk-Smith, 2005 ; Gueguen, 2001 ; Gustavson et al., 1987 ; Hold & Schleidt, 1977 ; Hirsch, 1993 ; Hirsch & Gruss, 1999 ; Kirk-Smith & Booth, 1980 ; Liljenquist et al., 2010 ; Razran, 1940 ; Sczesny & Stahlberg, 2002 ; Taylor, 1968 , p. 53). Footnote 4 As might have been expected, and as we will see later, there has also been extensive commercial interest in supporting claims around the role of fragrance in attraction/attractiveness—i.e., both in terms of a fragrance’s ability to boost the wearer’s self-confidence, but also to influence how they are perceived by others (Berliner, 1994 ; Hirsch, 2006 ). But, one might ask, are all the attributes/dimensions of person perception equally affected by the presence of scent/malodour, or are some judgments more malleable/important than others? And, if that is the case, how should any such differences be accounted for?

Furthermore, while significant crossmodal effects of olfactory stimuli on visual ratings of the attractiveness of those people shown in photographs have been demonstrated in many studies, not all studies have demonstrated such crossmodal effects (see Cann & Ross, 1989 ; Novak et al., 2015 , for a couple of null results). In the current academic climate, this naturally leads to concerns about power and reproducibility (Iso-Ahola, 2017 ; Open Science Collaboration, 2015 ; see also Syrjänen et al., 2021 ). As such, one of the other important questions to be addressed by this review is to try and identify some of the key factors that may be responsible for determining whether or not a crossmodal influence of olfaction on vision will be observed. Potentially relevant here, and as we will see time and again throughout his review, it is often unclear what exactly the link between the fragrance and the people that the participants were being asked to judge actually was. One might have imagined that establishing some meaningful connection between scent and sight would be a prerequisite for the former to influence the latter. However, somewhat surprisingly, that turns out not to be the case. Footnote 5

In the sections that follow, I will first review the literature that has investigated the influence of odour on person perception (“ The influence of odour on person perception ” section). First, the evidence concerning olfactory influences on attractiveness but also on a number of other qualities (such as beauty, charm, familiarity, intelligent, socially competent, and confidence) is reviewed. The various explanations for these crossmodal effects of olfaction on vision are summarized and the possible influence of visual stimuli on olfactory stimuli is also briefly discussed. In the “ Limitations/peculiarities of crossmodal research on olfaction on person perception ” section, I highlight a number of salient limitations/peculiarities in the literature examining crossmodal influences of olfaction on person perception. This includes everything from the familiarity (or otherwise) of the people whose pictures are being judged, through to the timing of the stimuli, and the lack of any explanation (to the participants) of what the connection between the scents they are smelling and the faces they are judging is. In “ The influence of a person’s natural body odour on multisensory person perception ” section, I move on to consider the influence of a person’s natural body odour on multisensory person perception, before summarizing the limited evidence regarding the impact of a person’s odour/fragrance, on their perception of themselves (see the “ Olfactory influence on perception of the self ” section). The “ Attractiveness as a multisensory construct ” section  briefly discusses the notion of multisensory attractiveness, and how the different sensory cues to person perception may be combined. “ Commercial interest in claims around the effects of fragrance on attractiveness ” section  switches briefly to consider the commercial opportunities around supporting claims concerning fragrance’s effect on person perception. Finally, in the “ Conclusions ” section, conclusions are summarized and directions for future research, as well as potential applications and implications of this research, are discussed.

The influence of odour on person perception

At the outset of this narrative review, it is important to note that there are multiple different kinds of situation in which olfactory stimuli may be present while we engage in person perception. On the one hand, one might be interested in the question of what role ambient (mal)odour plays in terms of personal attraction. However, there has been an explosion of research looking at the question of what a person’s body odour, or the use of personal fragrance (when presented prior to and/or while faces are being judged), may do in terms of the multisensory impression that they create, as well as how they make people feel about themselves. The evidence relevant to each of these cases below is reviewed in the following sections.

The influence of ambient scent on person perception

In those studies where an ambient scent has been introduced into a testing room, the natural presumption would be that whoever experiences the smell would attach it to the location, rather than necessarily to the individual faces that are flashed up briefly on the screen (as is typically the case in laboratory studies in this area). Nevertheless, despite the lack of a unity judgment (Chen & Spence, 2017 ), the (un)pleasantness of the ambient odour has nevertheless still been shown to influence judgments of interpersonal attraction, based on other people’s attitudinal questionnaire responses (Rotton et al., 1978 ; cf. Sczesny & Stahlberg, 2002 ; Experiment 1) or else, more commonly, their photos (e.g., Cann & Ross, 1989 ; Rotton, 1983 ). For example, Rotton investigated the influence of ambient malodour on 48 students’ ratings of four photographic negatives (taken from the school yearbook), four paintings, and four persons described by adjectives. Ethyl mercaptan (C 2 H 5 SH) served as the ambient malodour. This volatile chemical is described as smelling of rotting cabbage or sewer gas, though when presented in its pure form, as in Rotton’s study, it is apparently even more unpleasant/revolting. Hence, a highly aversive olfactory stimulus was used, with no meaningful connection to any of the visual stimuli that the participants had to rate. An elaborate ruse designed to make the presence of the malodour seem accidental was performed at the start of the experimental session. A between-participants experimental design was used with the participants rating the 12 visual stimuli once in either an odourless or else in the very malodorous room. The photos were rated on seven-point scales anchored with the words ‘zestful’ and ‘weary’ or ‘content’ and ‘irritable’. The people shown in the photographs were rated numerically (by about 5%), but not significantly ( p  < 0.07) as having less ‘energy’ and significantly lower ‘well-being’ (c. 10% change; p  < 0.01) in the polluted than the unpolluted room (see Table 1 for a chronological summary of psychophysical research investigating the crossmodal influence of olfactory stimuli on ratings of the attractiveness and other personal attributes of those shown visually). These early results therefore support the claim that ambient malodour affects person perception. Note also the small sample sizes involved in a number of the studies.

By contrast, however, Cann and Ross ( 1989 ) failed to demonstrate any such crossmodal effect of malodour on facial attractiveness. In particular, the male college students in the latter study had to rate a series of pictures of female faces while in the presence of either a pleasant fragrance ( Island Gardenia by Jovan which had a pleasant flowery aroma) or an unpleasant ambient odour (ammonium sulphide), or else in the absence of any olfactory stimulus. The photographs were rated using a 10-point attractiveness scale (anchored with the labels ‘extremely unattractive’ and ‘extremely attractive’) in a room that had been scented prior to the participants’ arrival. In this case, the presence versus absence of an ambient odour had absolutely no effect on the participants’ judgments of facial attractiveness. It should, however, be noted that the null effects reported in this case might well be attributable to the use of ambient room fragrancing, thus potentially reducing the likelihood that the participants would necessarily have associated the unchanging room odour with the sequentially presented faces. That is, there was little reason for the participants to believe that the faces and odours were connected, or that they belonged together and so should be unified (see Chen & Spence, 2017 , for the importance of the unity effect in multisensory perception). Indeed, Cann and Ross ( 1989 , p. 96) explicitly state that as the groups of four participants were being escorted to the testing room: ‘the experimenter apologized for the odor and claimed to have no knowledge about what had gone on before in the room to create the smell. This was intended to minimize curiosity about the odors’.

The rapid habituation of the olfactory system, especially under conditions of high visual load (see Forster & Spence, 2018 ) means that it is difficult to rule out the possibility that the odours might simply not have been consciously perceived for much of the latter part of the experimental session in Cann and Ross’s ( 1989 ) study. Footnote 6 The between-participants nature of the experimental design may also have contributed to the null results. Nevertheless, Cann and Ross ( 1989 , p. 99) ended up concluding that: ‘it may be that olfactory stimuli produce no reliable effects on judgments of attractiveness’. At the same time, however, they also allow for the fact that if olfaction’s effect on attractiveness ratings were to be based on mood enhancement then their study failed to demonstrate a robust effect on mood (despite the fact that ammonium sulphide is typically described as a very unpleasant olfactory stimulus).

Kirk-Smith and Booth ( 1990 ) conducted a study (reported in a book chapter) in which impregnating a face-mask with Shalimar perfume, Footnote 7 resulted in both male and female observers rating half-torso clothed photographs of males and females as looking significantly sexier and softer as compared with a no-perfume condition. By contrast, those participants who wore a face-mask that had been impregnated with banana essence exhibited no such crossmodal effect, perhaps due to the incongruence between the odour that they were exposed to and the photos that they had been requested to rate. Footnote 8 However, it is worth noting that the prolonged presentation of the odours meant that their presence may have elicited a change in participants’ mood. Indeed, the participants even rated themselves as feeling sexier after exposure to the Shalimar -impregnated face mask. Consequently, it is difficult to separate out the direct crossmodal effects of the presence of the odour on judgments of the people seen in the photographs from the more indirect effects that extended exposure to the perfume may have had on the mood of the participants, which, in turn, could have given rise to the behavioural effects that were reported. This possible explanation for the findings was one that Kirk-Smith and Booth themselves acknowledged.

Bensafi et al. ( 2002 ) conducted an event-related potential (ERP) study in which female volunteers had to discriminate whether a sequence of female faces were pleasant or unpleasant. Ratings were either carried out following the presentation of a pleasant floral odour for 5 s or else in a no odour baseline condition. (Note that no fragrance was presented while the face was being displayed on the screen.) Although the methods are a little unclear, it would appear as though the presence versus absence of the floral odour was switched half way through each block of 32 trials. However, there was virtually no difference in the percentage of faces rated as pleasant in the pleasant floral odour condition ( M  = 36.8%) as compared to the no odour baseline condition ( M  = 36.2%; comparison, n.s.). In this case, though, the use of a dichotomous response (rather than a more fine-grained rating of facial attractiveness as has been used in the majority of other studies) may have been at least partially responsible for the null result. At the same time, and as we will also see later, unpleasant odours generally tend to have a larger effect on attractiveness ratings than pleasant fragrances when compared to a neutral baseline (e.g., see Cook et al., 2018 ; Demattè et al., 2007 ; Li et al., 2007 ). In their study, Bensafi et al. also explicitly state that they made no mention to their participants that any scent would be presented, thus presumably leaving their participants uncertain of the crossmodal connection, if any, between the sensory stimuli that they experienced.

Generally speaking, the assumption in the literature would appear to have been that mood-based effects of olfactory stimuli on person perception are more likely to be observed in those situations in which the participants are exposed to a particular fragrance for a prolonged period of time (e.g., over a block of trials, or over an entire experimental session in between-participants studies). At the same time, however, it is worth remembering that any olfactory adaptation effects might well be expected to eliminate the effect of olfaction on mood over time. By contrast, in those studies that will be described in the next section, where the fragrance/smell has more often changed randomly on a trial-by-trial basis, there would seem to be little reason to believe that mood-induction provides a likely explanation for any crossmodal effects of odour that have been documented (as the timecourse is simply not appropriate).

The influence of hedonically valenced smells on multisensory person perception

In what was perhaps the first trial-by-trial study of the crossmodal influence of fragrance on ratings of visual attractiveness to have been published, Demattè et al. ( 2007 ) had 16 young females participants (mean age of 26 years) rate a series of 40 cropped youthful male faces on a 9-point visual scale (anchored with ‘most attractive’ and ‘least attractive’). On each trial, a fragrance (either pleasant or unpleasant, body-related or not; specifically Lynx deodorant, Footnote 9 geranium, body odour—BO, and rubber) Footnote 10 or else no fragrance was presented prior to a randomly selected face, which the female participants had to rate (see Fig.  1 ). On each and every trial, the participants reported whether or not a fragrance was present prior to the onset of the visual stimulus, thus ensuring that the participants had paid attention to the olfactory stimuli. Ratings of the male faces were significantly influenced by the pleasantness of the fragrance (by c. 5%), though (contrary to the experimenters’ expectations) the body-relevance factor had no influence on ratings. Rather, it turned out that presenting either of the two unpleasant odour(s) led to a significant reduction in the attractiveness of the male faces when compared to the neutral/no odour, or pleasant odour conditions (with participants’ ratings for the latter conditions not differing significantly). Given that the onset of the olfactory stimulus occurred 500 ms prior to the onset of the visual stimulus (with both stimuli then being presented together for a further 1000 ms), these results should perhaps best be considered in terms of crossmodal affective priming (about which, more below).

[Reprinted with permission from Demattè et al. ( 2007 , Figure 1)]

Timeline describing the experimental procedure used in Demattè et al.’s ( 2007 ) experiment to demonstrate the crossmodal influence of pleasant versus unpleasant olfactory stimuli on young women’s ratings of men’s faces. Note that the olfactory and visual stimuli were varied randomly on a trial-by-trial basis. Notice also how, like in the majority of other studies of olfactory influences on visual attractiveness, the onset of the olfactory stimulus occurred prior to that of the visual stimulus.

McGlone et al. ( 2013 ) conducted a functional MRI follow-up to Demattè et al.’s ( 2007 ) psychophysical study using much the same experimental procedure but this time with a new group of young female participants lying in the brain scanner rather than seated comfortably in the psychophysics laboratory. The same basic crossmodal (affective priming) effect of odour pleasantness on ratings of facial attractiveness was observed (in this case only the Lynx and artificial BO were used). The faces were rated as roughly 8% more attractive when preceded and accompanied by the smell of Lynx as compared to when accompanied by the synthetic body odour. Once again, there was no significant difference between the pleasant fragrance and the no fragrance control condition. A shift in the focus of activation within the neural representation of attractiveness that has been documented in orbitofrontal cortex (OFC), was observed. Note that the OFC has been implicated in encoding the reward value of stimuli (e.g., Kahnt et al., 2010 ). More specifically, when the faces were paired with the pleasant fragrance, increased activation was observed in the medial part of orbitofrontal cortex and ventral striatum. By contrast, when the same faces were paired with the unpleasant odour instead, the activation seen in the insula and amygdala, which is known to be involved in the processing of aversive stimuli, increased (see Fig.  2 ). These results were taken to support a genuine crossmodal perceptual effect of olfactory cues on the visual perception of attractiveness (i.e., rather than some kind of olfactorily induced response bias or halo effect).

[Reprinted with permission from McGlone et al. ( 2013 , Figure 6).]

Summary of neuroimaging results from McGlone et al.’s ( 2013 ) follow-up to Demattè et al.’s ( 2007 ) psychophysical study. The graph showing the average ( n  = 16 participants) percentage BOLD signal change in the peak voxels in both medial and lateral OFC for each of the five experimental conditions. Error bars depict the standard error.

Li et al. ( 2007 ) demonstrated that ratings of the likability of a selection of faces displayed on a computer monitor were influenced by the presentation of a scent, especially if the latter was delivered at a subliminal level. Participants rated the likeability of neutral faces (using a visual analog scale—VAS—anchored with ‘extremely unlikeable’ and ‘extremely likeable’) after smelling near-threshold pleasant (‘citral’), neutral (anisole), and unpleasant odorants (valeric acid). Note that when presented at suprathreshold levels, these stimuli are often described as smelling of lemon, ethereal, and sweat-like, respectively. In the experiment itself, the participants first sniffed one of four bottles and reported whether or not they had detected an odour. Immediately thereafter, the participants rated the likeability of one of 80 emotionally neutral faces presented on a computer monitor for 1200 ms (see Fig.  3 ). The valence of the odour significantly shifted likeability ratings only for those participants who lacked conscious awareness of the olfactory stimuli, as verified by chance-level trial-by-trial performance on the odour-detection task (i.e., the 15 participants with an unadjusted d′ prime of 0). The other group of 15 participants with an unadjusted d′ prime of close to 1, were classed as the conscious group. In other words, across participants, the magnitude of this crossmodal priming effect decreased as the sensitivity for odour detection increased, meaning that subliminal odours had a larger impact than did the supra-threshold odours.

[Redrawn from Li et al. ( 2007 , Figure 1).]

Schematic illustration of the experimental paradigm used by Li et al. ( 2007 ). Initially, each participant’s odour-detection thresholds were established using an ascending-staircase procedure (not shown). Next, the participants had to sniff a bottle, indicate whether or not it contained an odour, view a face stimulus, and thereafter rate the face in terms of its likeability.

The sequential presentation of olfactory then visual stimuli from different locations/sources (that were semantically unrelated with the possible exception of the sweat smell) would presumably have given the participants in Li et al.’s ( 2007 ) study little reason to want to combine (or multisensorially integrate) the scent and suprathreshold face stimuli consciously. That said, it is interesting to note that in the unconscious group, only the unpleasant (i.e., possibly semantically related) sweat stimulus differed significantly from the pleasant and neutral scent conditions. However, with the limited range of olfactory stimuli used by Li et al., it is simply not possible to determine in hindsight whether this was driven by the body-relevance of the odour, by its being unpleasant, or by some other, as yet unidentified factor.

Once again, therefore, Li et al.’s ( 2007 ) results would appear to be more consistent with a crossmodal affective priming account driven primarily by the presence of the unpleasant (and in this case unnoticed) scent prime. Affective priming refers to those situations in which an affective stimulus (i.e., prime) evokes an emotional response in a perceiver/participant that is then carried over to the processing of a subsequent stimulus (i.e., target), modifying affective evaluation of the latter stimulus (Hermans et al., 1998 ; Murphy & Zajonc, 1993 ; see also Forgas et al., 1984 ). The 18 participants in a methodologically complex study by Seubert et al.’s ( 2014 ) presented two faces sequentially on each trial. The first face was always the standard (showing someone of middle-age), while the second has been morphed to show either 25 or 50% more or less wrinkles and blemishes. The participants initially made a speeded two-alternative-forced—choice (2AFC) judgment concerning whether the second face looked older or younger than the first. On a third of the trials, the participants had to rate how attractive the second face was (on a 100-point VAS anchored with ‘extremely unattractive’ and ‘extremely attractive’). On another third of the trials, they rated how old the face/person was (in this case, the scale was anchored with < 25 years at one end and > 60 years at the other, with 5-year tick marks added along the scale). In the remaining third of trials, the participants rated the valence of the odour that had been presented in that trial.

The onset of the second face was preceded and overlapped with the presentation of one of five fragrances varying parametrically between 100% fish odour (negatively valenced) and 100% rose scent (positively valenced). As predicted, judgments of attractiveness (which rely on affective processing) were linearly affected by the valence of the concurrently presented odour, consistent with visual and olfactory cues to attractiveness being represented within a common affective neural system. By contrast, the presentation of the unpleasant odorants in the more putatively ‘cognitive-analytic’ age judgment task appeared to interfere with performance (see Fig.  4 for results). One obvious limitation with this study is that the speeded task that participants performed first on every trial presumably led the participants to weight the two attributes (age and beauty) rather differently due to the specific task demands. The extent to which this particular aspect of the experimental design may have skewed the pattern of results that were obtained is unclear. Once again, as we have seen for pretty much all of the studies reported in this section, the researchers concerned make no mention of their participants being told anything about the link between the odorants that they had been presented with and the visual stimuli that they were expected to evaluate.

[Figure reprinted with permission from Seubert et al. ( 2014 , Figure 3).]

Results of factorial analyses for categorical effects of odours and facial morphing on attractiveness ( A ) and age ( B ) and ratings in Seubert et al.’s ( 2014 ) study. Ratings were provided on a visual analog scale consisting of 100 sub segments, which in the case of age was anchored at 25 years and 60 years for ecological validity. Error Bars indicate ± 1 SE, asterisks indicate significant differences as revealed by post hoc t tests (* =  p 0.05, ** =  p 0.01, *** =  p 0.001).

A similar (affective priming) explanation would also seem to apply in the case of the influence of pleasant and unpleasant odours (jasmine vs. methylmercaptan, the latter delivering a rotten-cabbage-like odour), or a no odour baseline, on the hedonic evaluations of people’s faces that was demonstrated in a combined behavioural and ERP study reported by Cook et al. ( 2015 ). In this study, the odorant was presented for three seconds, and the picture was then presented one second after its offset. The participants rated each neutral expression face on a 101-point visual scale anchored with ‘very unpleasant’ and ‘very pleasant’. After having rated the face on each trial, the participants were then prompted to rate the intensity of the olfactory stimulus that had just been presented. The results revealed that even though the hedonic olfactory stimulus was presented before the to-be-rated face, it nevertheless still led to hedonic assimilation, with the presentation of the pleasant jasmine odour leading to the subsequently presented face being rated as significantly more pleasant ( M  = 55) than the same faces when rated in the absence of any olfactory stimulus ( M  = 53). The lowest pleasantness ratings were documented in those trials where the faces were preceded by the smell of rotten cabbage ( M  = 50; i.e., the pleasant–unpleasant difference once again amounted to a c. 5% change in ratings, just as in Demattè et al.,’s, 2007 , study). In a later study, Cook et al. ( 2017 ) went on to demonstrate that ratings of the pleasantness of happy and disgusted (i.e., emotionally expressive rather than neutral) faces were also modulated by the presentation of the pleasant versus unpleasant odour that onset 1–2 s prior to and overlapped with the presentation of the face stimulus for 300 ms.

The ERP results from Cook et al.’s ( 2015 ) study revealed that the odour-induced shifts in face evaluation were associated with amplitude changes in the late (> 600 ms) and ultra-late (> 900 ms) latency epochs. The authors write that: ‘The observed amplitude changes during the ultra-late epoch are consistent with a left/right hemisphere bias towards pleasant/unpleasant odor effects’. (Cook et al., 2015 , p. 1). They go on to conclude that their: ‘Results suggest that effects of pleasant odors on face evaluation were specific to the late component. During the ultra-late component, effects of pleasant and unpleasant odors were distinguished in the left and right hemispheres, respectively’. (Cook et al., 2015 , p. 9). In a subsequent study, the same group of researchers reported that the negative hedonic evaluation and ERPs elicited by the unpleasant odours were both strengthened on those trials in which the olfactory and visual stimuli were presented simultaneously as compared to when the picture was presented a second after the offset of the olfactory stimulus (Cook et al., 2018 ). On the basis of the combined psychophysical and ERP data from the latter study, these researchers concluded that the late-positive potential (LPP): ‘may represent the strength of the effects of unpleasant odour context on face evaluation that occur as a result of the temporal association between odour and face’. (Cook et al., 2018 , p. 26). Interestingly, however, and in contrast to their 2015 study using essentially the same methods, there was no longer any difference between the positive odour and neutral clean air conditions in either the sequential or the simultaneous condition (though the positive vs. negative odour comparison once again revealed a difference of c. 5% in face ratings).

Semantic olfactory priming based on gender-congruency

All of the studies reported in the previous section used hedonically valenced odours (either positive or negative) to affectively prime participants in a crossmodal manner prior to the presentation of the face stimuli. Other researchers, meanwhile, have studied the crossmodal semantic priming of vision by olfaction by, for example, presenting the scent of an apple prior to the picture of the fruit (semantically congruent) or a car, say (the latter being semantically incongruent; see Gottfried & Dolan, 2003 ; Grigor, 1995 ; see also Grigor et al., 1999 ). Neuroscientists have highlighted the role played by the hippocampus and orbitofrontal cortex in establishing crossmodal connections between semantically related visual and olfactory stimuli (Gottfried & Dolan, 2003 ). Similarly, other researchers have shown that olfactory cues can also prime visual self-recognition (Platek et al., 2004 ). In the latter study, for example, the participants detected pictures of their own faces more rapidly when presented together with their own smell than with that of someone else. Another kind of semantic priming has been shown to occur when the gender that is associated with a scent is used to prime, or modulate, the perception of sequentially/simultaneously presented gender-matched, as compared to gender-mismatched, faces.

In one of the first studies of this type, Capparuccini et al. ( 2010 ) sprayed an experimental room with one of Givenchy’s male or female perfumes ( Pi Neo or Angel or Demon , respectively) as the olfactory stimulus during visual assessments of a range of 10 attributes/qualities using 10-point Likert scales. The participants (male and female) had to rank five male and five female faces against the (neutral, non-sexual) adjectives of ‘familiarity’ and ‘confidence’, (the potentially less neutral adjectives of) ‘liking’ and ‘irritability’, (and the putatively more sexually pertinent adjectives of) ‘beauty’, ‘pleasantness’, ‘charm’, ‘intensity’, ‘sexual interest’, and ‘sexual attraction’. The fragrance was sprayed in the room prior to the participant’s arrival, and (once again) no explicit mention of its presence was made by the experimenters. Of particular interest to the experimenters in this case was the change in their participants’ ratings of the face between the experimental sessions in which the scent happened to be congruent versus incongruent with the sex of the participant that they had to rate. Rather surprisingly, it turned out that gender-congruency of the faces being rated didn’t appear to influence the pattern of results that were obtained.

Intriguingly, judgments of beauty and charm were both enhanced by the presence of a gender-congruent (with the participant) as compared to a gender-incongruent ambient fragrance, with beauty showing the largest effect. These results were taken to show that the use of sexually oriented perfumes (i.e., gender-congruent, though in this case, as we have just seen, the congruency was relative to the participant rather than the face being rated) can have relatively large effects on the judgment of the more hedonic (or affective) aspects of person perception. By contrast, the gender-congruency of the ambient fragrance had less of an influence on the more purely sexual judgments, and no effect whatsoever on the neutral non-sexual ratings of familiarity and confidence. Once again, though, with only one example of gender-congruent and gender-incongruent scent it is impossible to know whether similar crossmodal effects would necessarily have been documented were other male and female fragrances to have been used instead.

Elsewhere, Marinova and Moss ( 2014 ) reported that people’s ratings of various characteristics of person perception beyond just attractiveness or pleasantness were affected by the presence versus absence of gender-congruent versus gender-incongruent fragrance. The female participants who took part in this study had to rate 15 male faces (five of high attractiveness, five of medium attractiveness, and five of low attractiveness) on six attributes: attractive, reliable, outgoing, intelligent, wealthy, and socially competent. Ratings were made in the presence of a female perfume (incongruent condition), a male perfume (congruent condition), or a no perfume control condition, with participants randomly allocated to produce three groups of equal size (i.e., a between-participants experimental design was used). Spraying a room with four spritzes of fine fragrance prior to each participant’s arrival presumably created a somewhat ambiguous situation in terms of whether the scent was perceived by participants to be an ambient fragrance or else someone’s personal fragrance (cf. Pichon et al., 2015 ).

The results failed to reveal a main effect of perfume congruency on attractiveness ratings. However, the moderately attractive male faces were rated as significantly more attractive by those in the gender-congruent as compared to the gender-incongruent condition, thus giving rise to an interaction between perfume condition and attractiveness group. Nevertheless, those participants exposed to the gender-congruent fragrance still rated four out of the five so-called ‘halo’ Footnote 11 characteristics (namely, ‘outgoing’, ‘intelligent’, ‘wealthy’, and ‘socially competent’) more highly than those in at least one of the other two conditions. So, for example, those faces presented while sniffing the gender-congruent scent were rated as looking significantly more intelligent than when viewed in the absence of fragrance (the difference with the gender-incongruent fragrance in this case failing to reach statistical significance). These results therefore indicate that the presence of an ambient gender-congruent perfume can impact positively on first impressions beyond attractiveness. However, it is worth noting that the small sample size, coupled with the between-participants nature of the fragrance manipulation, likely limits the power of this particular study. Furthermore, the use of only one gender-congruent and one gender-incongruent fragrance again means that it is simply not possible to disentangle whether it is the perfume, or the gender-congruency with the faces, that is doing the work in terms of influencing participants’ ratings. In conclusion, given the lack of a main effect of olfaction on attractiveness, and given the between-participants manipulation of the olfactory stimulus, Marinova and Moss’s ( 2014 ) results might well be considered more likely to reflect olfaction’s effect on mood (cf. Kirk-Smith & Booth, 1990 ), rather than a direct crossmodal effect on attraction, leading to a halo effect that then carried over to influence other judgments about a person.

Finally, in a recently published study, Risso et al. ( 2021 ) had their participants rate the attractiveness of male and female faces presented on a monitor (on a VAS anchored with the terms ‘unattractive’ and ‘attractive’) while in the presence of no odour (air), a liquorice odour, or a caramel odour. These two food odours had been rated as more masculine or feminine, respectively, in a preliminary study with 12 food aromas. Footnote 12 In total, each one of 60 faces was paired once with each of the three odours. The odorants were presented from glass bottles, with participants instructed to sniff while viewing and rating the face on the screen. Once again, the participants were told nothing about the link between these suprathreshold food-related odours and the faces they saw. Nevertheless, the male faces were still rated as looking significantly less attractive in the presence of either odour (with a slightly, but significantly, bigger drop for caramel, whereas for the female faces, the only significant drop in attractiveness ratings occurred while sniffing the liquorice as compared to the caramel aroma, with ratings in the latter condition being no different from the no odour control. Footnote 13

Risso et al. ( 2021 , p. 1) interpreted their results as highlighting: ‘the importance of the synaesthetic associations between “gender” and odours on people's judgements of facial attractiveness’. While the notion of crossmodal correspondences probably fits better with the contemporary view of the consensual link that so clearly exists between gender and non-body-related scents (Spence, 2011 ; Zellner et al., 2008 ), one might wonder whether this requires an additional explanation for the crossmodal effects of olfaction on person perception over-and-above those that have been outlined thus far. Perhaps the simplest way to think about these results is in terms of crossmodal semantic priming in this case based on the gender that was associated with the scent (though see also Lindqvist, 2012a , 2012b ) . Footnote 14

Olfactory contributions to the perception of facial emotion

Beyond the effect of hedonically valenced or gendered olfactory stimuli on judgments of the attractiveness of faces (and, on occasion, other personal attributes), a separate line of experimental research has shown that hedonically valenced non-body-related odours can modulate (that is, either facilitate or impair) the speeded identification of facial emotion too (e.g., see Leppänen & Hietanen, 2003 ; Seubert et al., 2010a ). So, for example, Leppänen and Hietanen reported that their participants were able to recognize disgusted facial expressions more rapidly in an unpleasant odour context while happy expressions were recognized more rapidly in a pleasant odour context instead. The presence of pleasant versus unpleasant odours have also been shown to result in the enhanced recognition of both disgusted and happy facial expressions (Seubert et al., 2010b ; see also Li et al., 2020 ; Stankovic et al., 2020 , who presented isovaleric acid). Using functional MRI, Seubert et al. ( 2010a ) were able to demonstrate that the processing of disgusted faces was facilitated by the prior presentation of odour primes. In the latter study, non-body-related pleasant (vanillin) and unpleasant odours (H 2 S) were presented, and compared to a no odour baseline condition. However, regardless of the valence of the olfactory stimulus, a reaction time advantage (olfactory priming) was documented for the recognition of disgust, but not for the recognition of either happy or neutral faces.

Elsewhere in the literature, establishing the appropriate odour-induced context (positive strawberry, vanilla, and orange zest, vs. negatively valenced fish odour) has been shown to modulate the search advantage for happy facial expressions amongst neutral faces (Damjanovic et al., 2018 ). Other researchers, meanwhile, have highlighted how odour-evoked hedonic contexts influence the discrimination of facial expressions in the human brain (Kastner et al., 2016 ; Poncet et al., 2021 ). In the latter research, contextual valenced odours influenced the discrimination of a neutral face, and to a lesser extent of a face showing disgust, as indexed by an occipito-temporal facial expression-specific brain response. In particular, the neural response to the neutral faces was found to be respectively larger and lower in the context of pleasant and unpleasant odours as compared with the control odour.

According to research by Forscher and Li ( 2012 ), micro-fearful facial expressions are processed preferentially following olfactory priming by semantically unrelated negative odours (valeric acid—sweat/rotten cheese and hexanoic acid—rotten meat/fat) as compared to more neutral olfactory stimuli (grass/medicine and pine resin scents). Setting a congruent odour context has also been shown to facilitate the perception of low-intensity emotional facial expressions (Leleu et al., 2015a , 2015b ). That is, a congruent odour can help to reduce the amount of information that a participant needs to recognize a congruent emotional facial expression.

One final preregistered study that is worth mentioning here was reported by Syrjänen et al. ( 2017 ). These researchers observed that valenced odors exerted a much reduced influence over the evaluation of emotion in dynamic (i.e., rather than static) faces. As in another study from the same research group that was mentioned earlier (Novak et al., 2015 ), the dynamic facial stimuli morphed from neutral to emotionally expressive. The participants had to classify a series of dynamic facial expressions as happy or disgusted. Syrjänen and colleagues wanted to know whether the emotional evaluation of these facial expressions would be affected by exposure to a negatively valenced sweat-like, odour (valeric acid—sweat), as compared with a soap-like, positively valenced odour (lilac essence), or a no-odour control. However, the results revealed that the pleasant and unpleasant odours had no effect on the time needed by participants to recognize happy or disgusted dynamic facial expressions. Footnote 15 It is, though, perhaps somewhat unclear as to whether this null result should be attributed to dynamic nature of face stimuli, or else to the fact that these faces both started with the same neutral emotional expression. Furthermore, it can also be wondered whether the use of a blocked design, where the participants were exposed to each odour over a five minute block of trials (i.e., rather than a trial-by-trial design) might not also have contributed to the null results. It is perhaps also worth noting that performance in this task was quite high ( d' 2.5 for disgusted, and a d′ of a little over 3 for happy expressions). The latter observation is important inasmuch as it has been suggested, and, in fact, demonstrated that olfactory stimuli may have a more pronounced influence over visual perception under those conditions where the visual task is more ambiguous/difficult (e.g., see Forscher & Li, 2012 ; Mujica-Parodi et al., 2009 ; Novak et al., 2015 ; Rubin et al., 2012 ; Zhou & Chen, 2009 ; see also Leleu et al., 2020 ).

Some researchers have even argued for a superadditive brain response, based on inverse effectiveness, in response to the simultaneous presentation of subtle visual (facial) and olfactory cues linked to negative emotion (such as faintly fearful faces, and the negatively valenced odours described as smelling of ‘rotten fish’, ‘sweat/rotten cheese’, ‘rotten meat/fat’, ‘rotten egg’ when presented at a suprathreshold level, but here presented at a near-threshold level. Footnote 16 Taken together, the results that have been summarized in this section would appear to fit in a framework in which hedonically valenced contextual olfactory stimuli facilitate the processing of congruent (in terms of hedonics) facial expressions. This is evidenced behaviourally as an enhanced ability to process facial emotion. Neurally, the evidence further indicates that emotionally charged odours modulate visual cortical response to ensuing emotional faces (Forscher & Li, 2012 ; Seubert et al., 2010a ).

Are the effect of olfaction person perception bidirectional?

Before concluding this section of the review, it is perhaps worth considering the question of whether crossmodal/multisensory influences also operate in the reverse direction. It is certainly noticeable how the vast majority of the literature on multisensory person perception has tended to focus solely on any crossmodal influences of olfactory cues on visual assessments rather than vice versa. What is more, this asymmetry becomes all the more striking when considered in the context of the separate literature that has emerged over the last half century or so concerning the crossmodal correspondences that exist between odour and colour. In the latter case, virtually all of the research that has been published to date has tended to focus on those crossmodal influences operating in the opposite direction: Namely, researchers have almost exclusively focused on the influence of vision (colour) on olfaction, rather than vice versa (see Spence, 2020e , for a recent review).

One of the few exceptions to this general asymmetry in the literature on multisensory person perception comes from a study by Cook et al. ( 2017 ) in which the pleasant fragrance of jasmine was rated as smelling significantly more pleasant when participants were staring at a happy rather than at a disgusted face. Meanwhile, participants rated the negatively valenced odour of rotting cabbage as smelling more intense when staring at a disgusted as compared to a happy face (once again, note that the odours are not obviously person-related; cf. Hummel et al., 2017 ). That said, it should be stressed that the crossmodal effects of vision on olfaction were pretty small in magnitude in this case. Elsewhere, Incollingo Rodriguez et al. ( 2015 ) reported on a couple of studies in which their participants viewed images of heavy (i.e., overweight/obese) and normal weight individuals while smelling coloured substances that, unbeknownst to them, were actually odourless. Across the two studies, the olfactory stimuli were rated as smelling worse when they were paired with images of heavy individuals than when they were paired with images of thin individuals. Once again, therefore, such results hint at the possibility that crossmodal influences may sometimes be observed from visual cues (of faces or bodies) on olfactory judgments, even when no explicit link is made by the experimenters between the olfactory stimuli and the people shown on screen.

Interim summary

The results that have been reviewed in this section clearly reveal that hedonically valenced odours, as well as semantically meaningful odours (typically gender-congruent vs. gender-incongruent) can, and very often do, influence person perception. Both hedonically valenced, and gendered fragrances have been shown to influence ratings of the people shown in still, if not necessarily in dynamically changing, images (see Novak et al., 2015 ; Syrjänen et al., 2017 ). Meanwhile, combining the results reported by Capparuccini et al. ( 2010 ), Marinova and Moss ( 2014 ), and Seubert et al. ( 2014 ), it would appear that the crossmodal effects of olfaction on visual perception are typically more apparent for certain judgments (attributes) than for others. In particular, crossmodal effects on visual ratings appear most pronounced for judgments of facial attractiveness (considered part of the affective system and perhaps indexing mate-selection; see also Corley & Raudenbush, 2002 ) and the seemingly interchangeably used terms of pleasantness (Cook et al., 2015 , 2017 , 2018 ), likability (Li et al., 2007 ), and beauty (Capparuccini et al., 2010 ). Footnote 17 The evidence is much weaker for any crossmodal influences of hedonically valenced odours on the more neutral, or cognitively determined attributes of faces, for example, judgments of well-being (Rotton, 1983 ) or age (Seubert et al., 2014 ). And the limited research that has been published to date has failed to demonstrate any impact whatsoever of olfactory stimuli on judgments of neutral attributes such as ‘energy’ (Rotton, 1983 ), ‘familiarity’, or ‘confidence’ (Capparuccini et al., 2010 ). At the same time, however, a separate line of experimental research has repeatedly demonstrated how the presentation of hedonically valenced olfactory stimuli frequently do influence the perception (i.e., the detection/discrimination) of the emotion shown by faces too. The latter crossmodal effects typically, but not always, being shown when the hedonic valence of the olfactory stimuli was congruent with the to-be-judged facial emotion (e.g., a hedonically negative odorant with a disgusted face). And, as mentioned earlier, one other important factor that appears to modulate the influence of olfactory cues on visual person judgments is the difficulty, or ambiguity, of the visual task.

Thus, taken together, the evidence reported so far in this narrative review would appear to show that olfactory stimuli can (but by no means always do) influence visual ratings of other people (see Table 1 ). A priori, one might have expected to observe either crossmodal ‘assimilation’ or ‘contrast’ effects in visual person judgments following the presentation of a task-irrelevant olfactory prime (e.g., Deliza & MacFie, 1997 ; Li et al., 2007 ; Piqueras-Fiszman & Spence, 2015 ). It is interesting to note, therefore, that the vast majority of the studies reported in this section have documented that when a crossmodal effect is evidenced assimilation is nearly always the result (e.g., Demattè et al., 2007 ; Marinova & Moss, 2014 ; Risso et al., 2021 ).

Over the years, several distinct cognitive mechanisms have been put forward in order to try and account for the crossmodal influence of task-irrelevant olfactory stimuli on visual person judgments. In those early studies where the olfactory stimulus was manipulated on a block-by-block, or between-participants, basis, and thus where the participants were exposed to a particular ambient odour for longer (than in the case in trial-by-trial priming studies), the indirect consequences of a particular mood being induced as a result of exposure to the hedonically valenced odour has been suggested to be behind the changed ratings. However, in the majority of more recent studies, where the olfactory stimulus has been changed on a trial-by-trial basis, and has typically been presented prior to the visual stimulus, then crossmodal affective (in the case of hedonically contrasting odours), or semantic (in the case of gender-congruent versus gender-incongruent odorants) priming has been suggested as the most likely mechanism underpinning the crossmodal effects that have been reported (see Table 2 ).

However, rather than seeing these different explanations as being entirely mutually exclusive, it is perhaps worth highlighting the fact that both the affective priming and mood induction accounts involve an emotional response to smell, differing primarily in the timecourse of the crossmodal effects (or emotional response). Meanwhile, the crossmodal affective, semantic, and gender-based priming accounts are similar inasmuch as they all stress the (in)congruency of the signals presented to the two modalities, vision and olfaction.

At the same time, however, it is perhaps worth highlighting one other potential explanation for the crossmodal effects of fragrance, namely ‘halo dumping’, that was raised, although ultimately discounted, by Demattè et al. ( 2007 ). The notion of halo dumping first emerged out of research on olfactory–gustatory interactions (e.g., in fruitiness/sweetness perception) where it was argued that the failure to provide appropriate response alternatives (in this case concerning sweetness) can lead participants to ‘dump’ what they think about an easy to rate attribute, namely sweetness on the fruitiness rating scale, since that was the only that had been provided to them to express themselves (Clark & Lawless, 1994 ). In this case, providing a separate scale for participants to respond to both gustatory sweetness and olfactory fruitiness, eliminated the crossmodal effect of sweetness on participants’ fruitiness ratings. One might consider whether the few studies of the olfactory modulation of person perception where the participants have been given a number of different scales to rate a person’s attributes (six in the case of Marinova & Moss, 2014 ; ten in the case of Capparuccini et al., 2010 ; and two in the case of Seubert et al., 2014 ), presumably help to address this potential concern, as do McGlone et al.’s ( 2013 ) neuroimaging results (discussed earlier). Footnote 18 At the same time, however, it is also worth noting that the senses of taste and smell are much more closely connected (and hence easily confusable; Spence, 2015 , 2016 ) than are olfaction and vision. Footnote 19 This may perhaps reduce the likelihood of this potential alternative explanation for the data (though see also Kappes et al., 2006 ). Given that the halo dumping account has not reappeared in the literature since first being discounted by Demattè et al. ( 2007 ), it can presumably be ignored as a relevant potential explanation for the crossmodal effects under study.

What is far less clear, at least on the basis of the studies that have been reported thus far in this review is the extent to which the nature of the relationship between the odour and the people being judged affects the likelihood of significant crossmodal effects being observed. A priori, given the existing literature on multisensory integration, one might legitimately have expected the likelihood of observing crossmodal effects to vary as a function of the spatial, temporal, and/or semantic relation between the unimodal stimuli (e.g., Calvert et al., 2004 ). However, what is particularly striking, looking back over all of the studies that have been reviewed here, is how the experimenters have rarely, if ever, made mention of the fragrance(s) or what its/their role, or source, might be (e.g., Bensafi et al., 2002 ). As such, one would have thought that the participants would have had little reason to bind the visual stimuli shown on the computer, and hence not expected to smell, with the odour that was present in the room, in a bottle (Risso et al., 2021 ), or more commonly these days, delivered by means of an olfactometer. That crossmodal effects have so often been documented then perhaps hints at the ubiquity/robustness of such effects and their seeming insensitivity to the normal rules of multisensory integration, at least as they have been reported amongst the spatial senses.

Limitations/peculiarities of crossmodal research on olfaction on person perception

In this section, I would like to highlight some of the peculiarities, and hence possibly also limitations, of the majority of the crossmodal research on fragrance effect on various aspects of person perception reported in the previous section. A slightly more subtle distinction here is between the suggestion that spatiotemporal coincidence is simply less important for olfactory multisensory integration, and the claim that it would be important were such information to be available in the olfactory system, which it mostly is not (see Sela & Sobel, 2010 ).

Does familiarity matter?

The first thing to note is that unfamiliar faces have nearly always been used as stimuli. It is certainly possible that the presence of a given fragrance might be more likely to exert a crossmodal influence over judgments of those people whom we are unfamiliar with, rather than those whom we already know well (and hence have perhaps made up our mind about; Graham & Jouhar, 1980 ). Indeed, elsewhere in the world of multisensory research, it has, on occasion at least, been demonstrated that audiovisual interactions (namely the McGurk effect when elicited by gender-incongruent auditory and visual speech stimuli) is modulated by the participants’ familiarity with the person shown/heard in the stimuli that they are judging (see Walker et al., 1995 ; cf. Setti & Chan, 2011 ). Hence, in real-world interactions with those whom we are familiar, it might be assumed that ambient malodour, or personal scent, would exert less of an influence than might be suggested by much of the literature reviewed here. As yet, though, this question has not been addressed empirically.

What is the difference between pictures and real people?

Given that we do not expect static photos or even dynamic videos to smell, it is perhaps surprising that so many significant effects have been reported using such discrete unisensory stimuli. At the same time, however, one might have imagined that if we had to evaluate an actual person wearing a fragrance, then perhaps any effects of olfaction on person perception ought to be enhanced (given that real people do smell). As far as I am aware, the only study to have done something along these lines was reported almost two decades ago by Sczesny and Stahlberg ( 2002 ; Experiment 2). These researchers conducted a social psychology experiment in which the male or female participants ( N  = 116 in total) had to pretend to be a personnel manager conducting a job interview of a male or female confederate who entered the room wearing a typical male or female fragrance (the most extreme of 12 fragrances evaluated in a pre-test). A significantly higher number of the candidates wearing the male fragrance were offered a job than were those wearing either no perfume or else a female fragrance. It might have been expected that a violation of odour expectations would have been triggered by those wearing a gender-incongruent scent. This, in turn, might then have captured the participants’ attention thus eliciting a heightened evaluative response (either positive or negative, depending on the valence of the odour; Schneider et al., 1979 ). However, in the case of Sczesny and Stahlberg’s study, the gender-congruency of the scent did not much seem to matter. That said, it is hard to say any more about this particular case given that the identity of the fragrances used was never revealed. Once again, empirical evidence concerning the relative influence of scent on our ratings of those who are either physically present in front of us, or else merely depicted in a photo on a computer screen is also currently lacking (presumably, in-part, due to the difficulty of conducting research with real people). Footnote 20

How important is the use of static versus dynamic images

It is striking how all but one of the 16 studies reported in Table 1 used static images of people’s faces. Reasons to believe that this feature of the experimental stimuli used in the majority of the research in this area shouldn’t much matter comes from those findings showing that judgments of facial attractiveness tend to be highly correlated for static photos versus dynamic video clips (Roberts et al., 2009a , 2009b ). At the same time, however, the crossmodal research that has been published to date appears to suggest that olfactory cues exert much less of an influence over judgments of dynamic visual stimuli (e.g., morphing faces, Novak et al., 2015 ; Syrjänen et al., 2017 ), perhaps because the latter are more likely to capture a viewer’s attention (Krumhuber et al., 2013 ; Sato & Yoshikawa, 2007 ). Hence, given that in real life face-to-face encounters we normally do have access to dynamic facial cues, one might worry how much of an impact ambient or personal fragrance is really going to have.

How important is it that olfaction is nearly always presented first?

Another area where additional crossmodal research might be considered beneficial to developing a better understanding of the parameters influencing the crossmodal influences on person perception links to the role of the relative timing of olfactory and visual cues on the behavioural and neural effects that may be observed. In other areas of crossmodal priming research, useful information is often provided by assessing the timecourse of presentation of one stimulus on the perception of, or response to, another more or less closely related stimulus (e.g., Chen & Spence, 2013 ; Smeets & Dijksterhuis, 2014 ; Wang et al., 2020 ). What is noticeable about the majority of studies of olfaction’s crossmodal influence over visual judgments of people is how the onset of the olfactory stimulus nearly always precedes that of the to-be-judged visual face image (though see Cook et al., 2018 ). To the extent that the ordering of unisensory impressions is likely to be reversed in everyday life, one might again wonder just how relevant the tightly constrained laboratory research is to the kinds of crossmodal or multisensory interactions that are likely to be seen in a more ecologically valid real-life setting. At the same time, however, it is also important to bear in mind that sensory transduction of olfactory stimuli at the nasal epithelium takes several hundred milliseconds longer than the transduction of visual stimuli at the retina (see Spence & Squire, 2003 ).

It is perhaps relevant here to note that we typically make up our minds concerning a person within the first 100 ms of seeing them (Willis & Todorov, 2006 ), with ratings of attractiveness, likeability, trustworthiness, competence, and aggressiveness all being highly correlated with the judgments we make when not under time constraints. Survival-related judgments of threat from facial stimuli can be made based on whatever visual information is available during the first 39 ms of seeing someone (Bar et al., 2006 ), while their facial attractiveness can be estimated in nothing more than a glance (Olsen & Marshuetz, 2005 ). According to Carbon and colleagues, we can identify someone’s gender from a portrait after 244 ms, and rate their attractiveness just 59 ms later (Carbon et al., 2018 ; Dobson, 2018 ). Given the rapid processing of visual information, and the much slower processing of olfactory stimuli, one might therefore wonder whether this means that our mind has normally been made up on seeing someone for the first time prior to any olfactory cues generally becoming available and hence influencing our judgments subsequently, or retrospectively (see also Walla, 2008 )? This is where further crossmodal priming studies in which the stimulus onset asynchrony (SOA) between olfaction and vision is parametrically varied might be especially useful. The results of such research might then help to determine the ecological validity of crossmodal olfactory effects on visual judgments of people.

What role does scent attribution play?

There is an important question concerning the attribution of olfactory stimuli that runs through all of the research that has been reported thus far in this review. In particular, in none of the studies that were mentioned in the preceding section did the experimenter ever give their participants an explicit reason to link the odours to the unknown people whose images they were being asked to judge. As such, given how the majority of studies reported a significant crossmodal effect of olfaction on visual person judgments, one might be tempted to conclude that olfactory stimuli are automatically integrated with whichever other (visual) stimuli happen to be presented, or attended, at the time. The correlated delivery of scent and picture in many of the studies would suggest that approximate temporal coincidence certainly provides sufficient reason to bind (Cook et al., 2018 ). Of course, the claim that olfactory stimuli are simply bound with any visual stimuli that happen to be presented at around the same time, is certainly much harder to accept in the case of visual search studies, say, where multiple faces may be presented at the same time (see Damjanovic et al., 2018 ). This presumably giving rise to one version of what might perhaps be considered the olfactory version of the cocktail party effect (see Rokni et al., 2014 , for another).

It is, then, rather surprising that the attribution of the odour does not seem to matter in this case. The question of what, if anything, a participant attributes the scent’s presence to is simply left unmentioned. However, several possible alternatives immediately suggest themselves—people might attribute the odour to the environment (Rotton et al., 1978 ; see Spence, 2020c ), to the person that they happen to be evaluating at that moment (Demattè et al., 2007 ), or perhaps to the clothes that they happen to be wearing (Demattè et al., 2006 ; Laird, 1932 ). Footnote 21 Alternatively, however, the research also shows that olfactory cues may influence the perceived shininess of a person’s hair (Churchill et al., 2009 ), or even the product that they happen to be inspecting (Aikman, 1951 ; Ebster & Kirk-Smith, 2005 )? Intriguingly, the question of how to ensure the appropriate attribution of scent also arises in the case where film-makers have attempted to link particular scents, or fragrances to individual characters in the case of scented cinema; see Spence, 2020d , for a review). In one conference abstract relevant to this theme, Wille et al. ( 2003 ) had people watch videos while in the presence of a pleasant odour (including a jasmine-like fragrance), an unpleasant odour (indole), or else no odour. The presence of either odorant influenced the participants’ mental state while at the same time also leading to their rating the actors as looking more attractive. This is a somewhat counterintuitive result in the case of the negatively valenced smell of indole, though it is worth noting that, when questioned, the participants did not want to see more of the movie clips in that condition.

Given the lack of spatial information typically provided by our olfactory experiences (meaning that the location of the source of an olfactory stimulus is normally unavailable within the olfactory system), temporal coincidence, combined with semantic knowledge would appear much more important to determining what is bound with, or influenced by, a given scent (though see also Sela & Sobel, 2010 , for the suggestion that humans are in a constant state of olfactory change blindness). One other thing to note is that the rise of so-called gourmand fragrances—that is, fragrances that have a distinctly flavourful olfactory expression might be expected to make it somewhat harder for the perceiver/participant to attribute the fragrance to the correct source, given the more obvious semantic association with a real-world food source (see also Anon, 2008 ; Barr, 2020 ; Tanner, 2017 ). That is, it is unclear why exactly the smell of liquorice or caramel should have been bound with, or at least have influenced attractiveness ratings in Risso et al.’s ( 2021 ) study. Footnote 22

The influence of a person’s natural body odour on multisensory person perception

All of the research that has been reviewed thus far in this narrative review has relied on the presentation of non-body-related scents with the closest thing to natural body odours being the synthetic BO (thiol compound), used in the research by Demattè et al. ( 2007 ) and McGlone et al. ( 2013 ), and the synthetic sweat (valeric acid) used as a negatively valenced stimulus in the studies reported by Li et al. ( 2007 ), Forscher and Li ( 2012 ), and Syrjänen et al. ( 2017 ). However, a large body of research now shows that we are able to make approximate judgments about an individual based on nothing more than a brief exposure to their natural scent. Footnote 23 So, for example, as was mentioned in the Introduction, we can estimate a person’s rough age (Mitro et al., 2012 ), their sex (Schleidt et al., 1981 ), their health and emotional state (Chen & Haviland-Jones, 2000 ; including chemosensory signatures of fear and anxiety; de Groot & Smeets, 2017 ), and make informed guesses about three of the big five personality traits at a level that turns out to be significantly better than chance (Sorokowska et al., 2012 , 2016 ). We can even smell out those who are related to us (i.e., our kin; Weisfeld et al., 2003 ). In this section, I would like to briefly review the research that has been published on the multisensory integration of various body odours with visual judgments concerning person perception. Note that, in this case, it feels somewhat more natural to talk in terms of multisensory integration, rather than simply just crossmodal effects, given that every one of us has our own body odour (i.e., the various cues could potentially belong to the same person/object).

Chemosensory signals of anxiety and stress

The presence of sweat odour has been shown to increase the rated arousal of faces, and may also enhance the early allocation of attentional processes in the structural encoding of faces (Adolph et al., 2013 ). Mujica-Parodi et al. ( 2009 ) observed increased amygdala activation following the presentation of chemosensory stress stimuli. Indeed, threatening or fearful stimuli (such as fearful faces and stressed body odours activate the brain’s fear circuit including the amygdala (Novak et al., 2015 ; Rocha et al., 2018 ; Zald & Pardo, 1997 ). Rubin et al. ( 2012 ) reported that inhaling stress sweat enhances the neural response to neutral faces. Walla et al. ( 2003 ) used magnetoencephalography (MEG) to study olfaction and face encoding in humans.

Elsewhere, it has been shown that the positive emotional priming of the perception of facial affect in females is diminished in the presence of chemosensory anxiety signals (Pause et al., 2004 ). Specifically, the presence of chemosensory anxiety signals collected from men awaiting an exam was shown to reduce the priming effect of a briefly presented happy face presented prior to a neutral face (rated for facial affect) in women, but not in males, The presentation of stress chemosignals have also been shown to influence social judgments of people (women) shown in videos (Dalton et al., 2013 ). In particular, the women shown in video scenes were rated as being more stressed by both men and women when in the presence of stress sweat. The male participants also rated the women in the videos as looking less confident, trustworthy and competent when smelling the stress or exercise sweat (as compared to deodorized stress sweat condition).

Rocha et al. ( 2018 ) demonstrated that the presentation of BO sampled from individuals who were anxious induces a stress response and, at the same time, can bias the recognition of dynamic facial expressions, when compared with the BO taken from relaxed individuals. The participants ( N  = 46) had to categorize the emotion of a face that morphed from a neutral expression to either an angry or happy expression, during exposure to either stressed or relaxed BO. Exposure to the anxiety BO increased the accuracy of dynamic facial recognition (while, at the same time, reducing parasympathetic cardiac activity). These results therefore suggest that those components of BO that are associated with anxiety induce a stress response in recipients, modulating both their arousal and cognitive-emotional skills but at the same time facilitating the processing of emotional facial stimuli (cf. Mutic et al., 2019 ). The presence of a fear odour facilitates the detection of fearful expressions over other negative expressions (Kamiloglu et al., 2018 ; cf. Jessen, 2020 ). Meanwhile, Zhou and Chen ( 2009 ) found that the chemosignal of fearful sweat biased women toward interpreting ambiguous facial expressions as more fearful, but has no effect when the facial emotion was more obvious (see also Prehn-Kristensen et al., 2009 ).

Non-fear/anxiety related chemosensory body odours

The presence of human sex hormone-like chemicals also influence people’s ratings of the perceived masculinity/femininity of the faces shown on the computer (see Kovács et al., 2004 ; see also Zhou et al., 2014 ). A single intranasal dose of the neuropeptide oxytocin (involved in attachment behaviours) has been shown to enhance the facial judgements of attractiveness and trustworthiness with respect to an intranasal dose of placebo (Theodouridou et al., 2009 ). Meanwhile, Striepens et al. ( 2014 ) found that oxytocin enhances the perceived attractiveness of unfamiliar female faces.

Conditioned responses to body odours

At this point, it is perhaps worth drawing attention to the fact that people develop conditioned associations with the body odours of attachment figures—think here only of the calming scent of a loved one (Granqvist et al., 2018 ; Hofer et al., 2018 ; McBurney et al., 2006 , 2012 ; Shoup et al., 2008 ; though see also Black, 2001 ). There is also growing evidence of the importance of maternal odour to the perception of faces in newborns (Leleu et al., 2020 ; Rekow et al., 2020 ). Meanwhile, some years ago now, Sullivan and Toubas ( 1998 ) described the positive effect that maternal odour had on soothing (i.e., reducing crying) and feeding preparatory responses (i.e., mouthing) in newborn (breast- and bottle-fed) babies.

In adults, such crossmodal effects are presumably based on an individual’s prior emotional experiences (see also Janssens & De Pelsmacker, 2009 ). Though, in such cases, it may be difficult to rule out any influence of the intrinsic qualities of the body odour from the positive associations that have subsequently been conditioned through extensive repeated exposure to the odour. In the future, it would be interesting to know whether a fine fragrance that was robustly attached to a loved one (should they always choose to wear the same scent) might take on some, or even all, of the same-stress reducing properties as body odours, or whether instead there is something special about the latter (see Boyle et al., 2009 ; Lundstrom et al., 2008 ; though see also Cecchetto et al., 2020 ).

On the surprising relationship between body odour and fragrance choice

In many parts of the world, people choose to mask our personal odours (Schleidt et al., 1981 ; see also Ferdenzi et al., 2013 ; König, 1972 ). That being said, there is an intriguing emerging literature on the non-random nature of the fragrance choices that we make, and how they may actually serve to, in some sense, amplify the olfactory signals that we give off naturally (see also Veitinger, 2015 ). Footnote 24 So, for example, Allen et al. ( 2016 ) demonstrated that the rated femininity of body odour was enhanced by the use of fragrance in women (though not in men). Milinski and Wedekind ( 2001 ) reported evidence of major histocompatibility complex (MHC)-correlated perfume preferences in people (see also Hämmerli et al., 2012 ). Meanwhile, Lenochová et al. ( 2012 ) found that the mixture of a person’s body odour with their preferred choice of perfume (taken from 12 young male adult donors) was rated as significantly more pleasant by a group of 21 young female adult assessors than when the male donor’s body odour was mixed with another (equally pleasant) fragrance chosen (randomly allocated) by the experimenter instead (see Fig.  5 ). Hence, while personal fragrance is undoubtedly an artificial creation, it may come to take on at least some of the role of authentic body odours (in providing an attractive olfactory signal), should it be experienced on an individual sufficiently often (see also Behan et al., 2006 ).

[Figure reprinted with permission from Lenchová et al. ( 2012 , Figure 4). https://doi.org/10.1371/journal.pone.0033810.g004 .]

Ratings of own and assigned perfume-body odour blends in Lenochová et al. ( 2012 , Study 3). Z -scored mean ratings (6 SEM) of attractiveness, pleasantness and intensity of perfume-body odour blends in individual male odour donors and for all donors together. Empty bars signify own and preferred perfume while shaded bars represent randomly assigned perfume combined with donor’s individual body odour.

Body odours provide a rich source of information (albeit often perceived unconsciously; Lübke & Pause, 2015 ; Parma et al., 2017 ; Pause, 2012 ) about a number of personal qualities. Footnote 25 Given that they constitute an intrinsic part of a person’s make-up, combining them with other attributes of person perception should perhaps best be considered as an example of multisensory integration (i.e., rather than as a crossmodal effect). At the same time, however, it is important to note that the body odours used in the majority of studies have been taken from other individuals than those assessed visually. This means that while the odour might be construed as, in some sense, congruent, it did not originate from the same person/object. Body-related chemosensory stimulation can, though, sometimes interfere with the visual information processing of faces (cf. Walla et al., 2005 ). And, more generally, it has been reported that odour perception can interfere with verbal processing (and vice versa; see Lorig, 1992 ; Walla, 2008 ; Walla et al., 2003 ; see also Zhou et al., 2019 ).

Olfactory influence on perception of the self

While the majority of the research that has been published to date has tended to focus on the effect of scent/odour on the perceiver’s perception of other people, there is also likely an impact (especially of one’s own body odour, or scent) on self-perception too, in terms of relaxation, self-confidence, mood, and/or arousal (Graham et al., 2000 ; see also Eli et al., 2000 ). At the same time, however, it is worth noting for how long (historically speaking), and how frequently (especially nowadays), people have been scenting themselves. According to Stoddart ( 1990 ), the use of perfumes and fragrances dates back at least as far as the ancient Egyptians and Greeks. In one UK study, 79% of the women and 60% of the men sampled reported using a deodorant every day (Roberts et al., 2010 ). People use fragrance and deodorize themselves for various reasons, including everything from the avoidance of being stigmatized through to enhancing the sense of personal appeal and confidence (Freyberg & Ahren, 2011 ; Waskul & Vannini, 2008 ).

In one elegant study, researchers were able to show how the simple manipulation of a man’s body odour (malodour) altered their self‐confidence as well as their judgements of how visually attractive they were to women (Roberts et al., 2009a ). Other researchers, meanwhile, have evaluated both the psychological and physiological effects of perfume on the emotional responses of menopausal women (Abriat et al., 2007 ). The presentation of a human sex steroid derived compound resulted in increased physiological arousal in women, while decreasing arousal in men (Bensafi et al., 2003 ). Meanwhile, the fragrance in certain skin creams has also been shown to help relax the wearer, and by so doing may temporarily reduce the facial evidence of wrinkles (Abriat et al., 2004a , 2004b ). A number of studies have now shown that both females and males who have been sprayed with either underarm secretions or with one of a number of different synthetic pheromones tend to engage in significantly more everyday sociosexual activities, including sexual intercourse, sleeping next to a partner, formal dating, petting, and affectionate kissing than control participants (e.g., Cowley & Brooksbank, 1991 ; Cutler, 1987 ; Cutler et al., 1998 ; Gower & Ruparelia, 1993 ; McCoy & Pitino, 2002 ; see Schaal & Porter, 1991 , for a review).

In research conducted in collaboration with scientists working at Unilever Research (makers of the Lynx/Axe deodorant that was mentioned earlier), Roberts et al. ( 2009a , 2009b ) gave one group of young men a control aerosol body spray without odour to use over a period of 72 h. Another group of participants were given a body spray containing a proprietary fragrance oil and an antimicrobial ingredient aimed at reducing malodour ( N  = 35 participants in total). The participants were subsequently instructed to rate how attractive they thought they were to the opposite sex on the basis of photos and short videos that they made specifically to appeal to those of the opposite sex. The results revealed that those given the active body spray felt more self-confident than those with the control spray (presumably due to the reduced malodour). They also rated themselves as being more visually attractive to women. Notice here how it is the effect of odorant on the wearer that is key to the effects that are observed. Although there was no difference between groups in mean attractiveness ratings for the static photos by a panel of females, the same women judged men using the active spray as more attractive in video-clips, suggesting a behavioural difference between the groups. Such results might once again be taken to highlight the methodological concern, highlighted earlier, around whether one chooses to use static or dynamic images of people.

There is also an emerging literature on the possibility of modifying body image by means of olfactory cues in the context of one’s virtual reality (VR) avatar (see Brianza et al., 2019 ). The latter researchers used a computer-based body visualization tool following one minute of walking in VR, with the scents being sprayed three times during that period. In particular, the results of the latter’s preliminary research suggested that the scent of lemon resulted in the participants reporting that they felt lighter while the vanilla scent made them feel heavier (cf. Hirsch et al., 2003 ). Once again, here, the ‘meaning’ or association primed by the scent can perhaps best be understood in terms of crossmodal correspondences (see Deroy et al., 2013 ; Spence, 2011 ; cf. Risso et al., 2021 ).

As well as its role in boosting the wearer’s self-confidence, fragrances are sometimes also used to help people get into a particular mood/state of mind. Relevant here actors have, on occasion, anecdotally reported how they sometimes wear a particular fragrance in order to help them get into the role that they are playing (see Spence, 2021b ). For instance, according to actress Alla Demidova, the actor Vladimir Vysotsky brought bottles of Parisian perfume to spray on them before performing (as Ranevskaya and Lopakhin, respectively) in The Cherry Orchard (Alipaz, 2015 ).

Attractiveness as a multisensory construct

Judgments of the attractiveness of a person’s body odour have in some cases been shown to correlate with judgments of the attractiveness (or symmetry) of their face (Rikowski & Grammer, 1999 ), and even with attractiveness judgments (which are sometimes equated with judgments of mateworthiness) based on the sound of their voice (Cornwell et al., 2004 ). For instance, Rikowski and Grammer highlighted the existence of a significant correlation between the rated sexiness of a man’s body odour and his facial attractiveness to females. Such findings have led on to discussion in the literature of whether the different senses should be considered as providing redundant, partially redundant, or independent cues to person perception (see Feinberg et al., 2005b ; Zuckerman et al., 1991 ), and specifically to judgments of a person’s beauty (Groyecka et al., 2017 ). Groyecka et al. discuss these three alternative evolutionary hypotheses aimed at explaining the function of multiple indices of attractiveness. Indeed, Groyecka et al. ( 2017 , p. 1) talk of: ‘the critical need to incorporate cross-modal perception and multisensory integration into future research on human physical attractiveness’. To the extent that it is relevant, the suggestion from those working with other species is that mate selection based on the evaluation of multiple sensory cues (whether or not they happen to be integrated into an overall multisensory assessment) likely represents a more successful mating strategy (Møller & Pomiankowski, 1993 ). At the same time, however, they also highlight the fact that more research is needed, saying that: ‘The complexity of what people perceive as attractive highlights the need for more research on the multimodal nature of person perception, as challenging as this may be. In addition to studying each modality as if it exists independently of the others (which in the real world it most often does not), researchers have focused disproportionately on visual indicators of attractiveness, underplaying the influence of scent and voice’. (Groyecka et al., 2017 , p. 3).

There is also a literature on MHC, a set of genes involved in immune function. This olfactory signature provides clues as to the genetic compatibility (i.e., viability/health) of any potential offspring (Chaix et al., 2008 ; Havlicek & Roberts, 2009 ; Havlíček & Roberts, 2013 ; Penn et al., 2002 ; Roberts et al., 2005a , 2005b ; Santos et al., 2005 ; Wedekind et al., 1995 ; Winternitz et al., 2017 ; see also Jacob et al., 2002 ). Perhaps unsurprisingly, the growing evidence concerning the informative nature of a person’s body odour in terms of chemosensory communication (Russell, 1976 ) has also led to growing artistic interest in the idea of the smell dating agency The basic idea here is that people choose their date based on the unfragranced smell of t-shirts after having been worn (Jamieson, 2016 ). Such an approach has at least some support from the empirical research (Roberts et al., 2011 ). That said, when Foster ( 2008 ) compared the attractiveness ratings made by 44 female participants on sniffing used t-shirts, viewing pictures, or sniffing t-shirts while looking at photos of 21 men, the photos were found to be a much better predictor of overall attractiveness ratings of than were the smelly t-shirts, with the latter only predicting attractiveness amongst the women who were fertile (i.e., those who were not using hormonal birth control). At the same time, however, it has also been shown that women’s preference for dominant male odour may be influenced both by the menstrual cycle and their relationship status (see Havlíček et al., 2005 ). In a highly cited study, Miller et al. ( 2007 ) assessed the tips reported by 18 professional lap-dancers working in gentleman’s clubs over a 60-day period. The results showed that normally cycling participants earned about US$335 per 5-h shift during estrus, US$260 per shift during the luteal phase, and US$185 per shift during menstruation. By contrast, those lap-dancers using contraceptive pills showed no estrous peak in their earnings.

It is not only the role of fertility in attractiveness, though, that separates the sexes. There are also important differences between women and men in terms of scent sometimes having more of an influence over the perception and behaviour of women (Chen & Haviland-Jones, 2000 ; Doty et al., 1985 ; though see also Brand & Millot, 2001 ; Doty & Cameron, 2009 ; Koelega & Köster, 1974 ). Women have also been reported to rate smell as a more important sense in mate selection whereas men report valuing visual cues more highly (Havlíček et al., 2008 ; Herz & Inzlicht, 2002 ; though see also Johansson & Jones, 2007 ; Sorokowska, 2013 ).

Commercial interest in claims around the effects of fragrance on attractiveness

Given the size of the market, not to mention its longevity, it should not come as any surprise to recognize that there has been a great deal of commercial interest in supporting claims around the effectiveness of personal fragrance (Brady, 1978 ; Gilbert & Firestein, 2002 ). Over the years, there has understandably been a great deal of commercial interest by those wishing to capitalize on marketing opportunities associated with functional fragrance claims. Indeed, it is noticeable how many of the studies that have been reported in this review were either funded by the fragrance houses or the home and personal care (HPC) companies, and/or were co-authored by those working within such establishments. At the same time, however, there is also a separate literature relating to patents around the ability of certain olfactory stimuli to influence person perception (e.g., Berliner, 1994 ; Hirsch, 2006 ).

For instance, according to a 2006 patent application submitted by Dr. Alan Hirsch, the suggestion is made that the administration of a certain odorant or combinations of odours may provide an effective means of enhancing a woman's self-confidence. The application talks of an odorant or odorant mixture that contains grapefruit, and preferably pink grapefruit, as the dominant odorant. Elsewhere, grapefruit combined with vanilla, and baby powder odorants is suggested to be especially effective . The patent makes the claim that smelling such an odorant/odorant mixture for somewhere between three seconds and a minute, but preferably for at least 20 s will reduce a man’s anxiety and also elevate his sense of well-being. In turn, this will result in his having a more positive view of the physical attributes of the woman, for example, perceiving her to be younger than without the fragrance. The magnitude of this crossmodal effect on age perception is suggested to be about 10% (or 4–10 years). Hirsch goes on to suggest that knowing this crossmodal effect of fragrance on male observers may also help to reduce a woman’s anxiety (and at the same time enhance her sense of well-being).

In the research supporting the patent application the influence of impregnating a face mask with grapefruit, grape, or cucumber odour on age judgments are compared. The participants ( N  = 37) were shown photos of 20 individuals and asked to estimate the age of the person shown in each of the images. (The description is, though, unclear about whether this is between- or within-participants design, nor is it clear what proportion of participants were male or female.) The suggestion is that biggest effects observed with men rating women where 6 years reduction mentioned. By contrast, the grapefruit fragrance had no effect of women’s ratings of the age of either male or female photos. However, there is insufficient detail to know to what extent the effects stand up to rigorous statistical analysis. Footnote 26

Hirsch ( 2006 ) suggests that a familiar odorant may semantically prime thoughts of people of a given age. In the patent application, Hirsch writes that: ‘The subject's past experience with an aroma and the person in the subject's life who wore the aroma may impact age perception’. He continues: ‘The grapefruit aroma may have acted as a rejuvenator through the mechanism of context-dependent learning’. Giving a concrete example Hirsch then suggests that: ‘a subject whose grandmother often wore lavender may consciously or Sub-consciously associate lavender with octogenarians, whereas the aroma of cotton candy may remind them of more youthful acquaintances. Thus, the aromas, which are traditionally used with older individuals, would act to increase the perceived age where traditionally more youthful smells would serve to induce a rejuvenating effect’. Taken together, the crossmodal effects on age judgments claimed by Hirsch would appear to involve both the indirect effects of mood-induction as well as the semantic priming of age.

In future research it will be interesting to assess the extent to which the laboratory-based crossmodal effects of olfaction on visual ratings of attractiveness, age, or any other attribute, be it of others or of the self, extend to the situations of everyday life (Kirk-Smith & Booth, 1987 ). In this regard, Roberts et al.’s ( 2009a ) study perhaps comes closest to bridging the sometimes wide gap between well-controlled laboratory studies and ecologically valid real-world studies (see also Sczesny & Stahlberg, 2002 ).

Conclusions

According to the majority of the research that has been reviewed here, it would appear that olfactory cues, no matter whether (or even if) they are related to an individual often influence various aspects of person perception, typically operating at a sub-conscious level (see Capparuccini et al., 2010 ; Li et al., 2007 ; Novak et al., 2015 ; see also Coleman, 2021 ; Holland et al., 2005 ; Kirk-Smith et al., 1983 ; Parma et al., 2012 ). Such crossmodal and multisensory effects can be seen as running counter to the widespread dominance of the visual in everyday life (see Hutmacher, 2019 , for a review), and the long history of downplaying the importance of the olfactory sense in humans (see McGann, 2017 , for a review). Footnote 27

While acknowledging the importance of the area, it is also true that further research is needed, as highlighted by the following quotes from researchers working in the area. For instance, Roberts et al., ( 2009a , 2009b , p. 47) note that: ‘Artificial fragrances have been used for thousands of years to manipulate personal odour, but the nature and extent of influences on person perception are relatively unexplored’. (see also Classen et al., 1994 ). Meanwhile, according to Seubert et al. ( 2014 , p. 6): ‘While olfactory effects on person perception have long been neglected in the laboratory, this study stresses that such effects likely have an important effect on the affective connotation of real-life social interactions and deserve further attention’.

One point that has been stressed repeatedly in reviewing the research is how the participants in the majority of studies have been given no information about, or explanation for, the presence of fragrance in the studies in which they take part. While on the one hand this may help to avoid demand characteristics (namely, participants responding in the way that they expect the experimenter wants them to; see McGlone et al., 2013 ; Rosenthal, 1964 , 1966 , 1967 ) it also makes the demonstration of crossmodal/multisensory effects of olfaction on person perception all the more surprising, suggesting that the effects are automatic and seemingly require no conscious attribution of scent to the individuals that they rate. The fact that sub-threshold smells have been documented to influence person perception (Li et al., 2007 ) and that crossmodal effects on attractiveness have been shown to influence neural activation in those brain regions that are known to be sensitive to the reward value of facial attractiveness (McGlone et al., 2013 ) both hint at the existence of a genuinely perceptual crossmodal effect of olfaction on person perception in addition to any olfactorily induced response biases that may sometimes also be picked up.

Perhaps unsurprisingly given what we have seen in this review, those who do not have a functional sense of smell (due to congenital anosmia) have been shown to have anomalous interpersonal relationships (as a result of increased social insecurity; Croy et al., 2013 ). Given the long-lasting chemosensory impairments reported by many of those who contract Covid-19 (Carfi et al., 2020 ; Gallagher, 2020 ) there may be serious, if as yet unacknowledged problems. It turns out that most of us will sniff our hand within a minute of shaking another’s hand (Frumin & Haviv, 2015 ). Although most of us are unaware of doing it, the suggestion is that this behaviour likely enables us to pick up biologically relevant chemosensory cues about those we meet. At the same time, however, one might be concerned how the elimination of the handshake and the often mandated wearing of facemasks while out in public (Carbon, 2021 ) is presumably substantially interfering with our normal olfactory perception of others (see Spence, 2020b , for a review). It is in this context that Kirk-Smith and Booth’s ( 1990 ) somewhat unusual approach of scenting facemasks with a commercially available fragrance (and banana essence) suddenly appears far more relevant (cf. Hirsch, 2006 ).

As highlighted by this review, a broad range of crossmodal/multisensory effects of olfactory cues on multisensory person perception (whether that person happens to be the perceived themselves, or someone else) have been documented in the literature. In terms of the putative mechanisms underlying such effects, the emotional response to olfaction (be it mood induction, or crossmodal affective priming) appears to offer one account while others have highlighted the importance of (in)congruency between the sensory stimuli, be it in terms of affective, semantic, or gender-based crossmodal priming. However, it should also be noted that in terms of how people (and other species) go about rating of attractiveness of others, multiple evolutionary accounts have been suggested (Groyecka et al., 2017 ).

One area that has not been covered in this narrative review concerns the long history of studies that have investigated the evaluative conditioning of affective responses to faces by means of pairing them with odour (e.g., Gottfried et al., 2002 ; Steinberg et al., 2012 ; Todrank et al., 1995 ; see also van Reekum et al., 1999 ; van den Bosch et al., 2015 ; and see Syrjänen et al., 2021 , for a recent review of olfactory influences on facial attractiveness).

Implications of crossmodal influences of odour

Those interested in the social aspects of cognitive/experimental psychology (such as the presence versus. absence of another person affecting task performance) might do well to keep in mind the possible role of the body odour/personal scent of the other, no matter whether it happens to be a co-participant, or an experimenter in the testing room, on performance (e.g., Barutchu & Spence, 2020 ; Lundstrom & Olsson, 2005 ). One could also imagine how those studies reporting effect of gender of experimenter might also highlight an, as yet, unacknowledged role for olfactory cues.

Impression management

Gaining a better understanding of the multisensory (especially non-visual) contributions to person perception (e.g., Dalton et al., 2013 ; Pause et al., 2004 ) is all the more important when it is realized just how influential visual judgments of personality characteristics such as competency (Todorov et al., 2005 ), aggressiveness (Carré & McCormick, 2008 ; Carré et al., 2009 ), and trustworthiness can be (Stirrat & Perrett, 2010 ; Wilson & Rule, 2015 ). Beauty too has been demonstrated to bias outcomes in the job market, not to mention life more generally (e.g., Hamermesh & Biddle, 1994 ; Maestripieri et al., 2016 ; Mulford et al., 1998 ), in part via the halo effect mentioned earlier. And while there is an analogous literature on the consequences of vocal qualities, such as pitch (e.g., in terms of the electability of politicians; Klofstad, 2016 ; Klofstad & Anderson, 2018 ; Tigue et al., 2012 ) and fundamental and formant frequency (e.g., on ratings of attractiveness; Feinberg et al., 2005a ; cf. Leongômez et al., 2017 ), there has been virtually no research looking at crossmodal judgments of voice being influenced by olfactory cues (though see Aglioti & Pazzaglia, 2011 ; Ferdenzi et al., 2016 ; Groyecka et al., 2017 ; Wesson & Wilson, 2010 , 2011 , for the slowly emerging interest in crossmodal interactions between this particular pair of senses). Nevertheless, the many crossmodal effects of body odour and fragrance on multisensory person perception undoubtedly support earlier claims regarding the importance of scent to multisensory impression management (e.g., Baron, 1981 , 1983 ; Dabbs et al., 2001 ; Fiore, 1992 ; Higuchi et al., 2005 ; Kirk-Smith & Booth, 1987 ; König, 1972 ; Nezlek & Shean, 1995 ; cf. Lobmaier et al., 2020 ), while at the same time contradicting earlier claims that olfaction was irrelevant to social interaction (see Argyle, 1975 , pp. 227, 327).

Digital olfaction and the mediated self

Looking to the future, there are many in the world of human–computer interaction who are actively considering the potential inclusion of scent in digital devices (e.g., Bodnar et al., 2004 ; Braun et al., 2016 ; Brewster et al., 2006 ; Dobbelstein et al., 2017 ), given the explosion in online dating, not to mention the release of scent-enabled mobile phones (see Gray, 2007 ). It is, though, important to highlight the very limited range of scents that even the latest olfactorily enabled consumer devices can achieve (see Spence et al., 2017 , for a critical review). As such, the most likely usage scenario might be to fill a scent-dispensing plug-in with your loved one’s perfume/aftershave and have a squirt be dispensed whenever they call you on their mobile device. However, while such a scent is likely to be positively valenced for the perceiver, despite almost four decades of research on scent’s effect on person perception, it is still not known whether it will convey exactly the same benefits in terms of reducing anxiety, etc., that the smell of a loved one’s body odour has been shown to do (Granqvist et al., 2018 ; Hofer et al., 2018 ; McBurney et al., 2006 ; cf. O’Brien, 2018 ). This, then, is just one of the questions still awaiting resolution in this most intriguing of research areas at the borders of basic and applied cognitive/perceptual research in experimental psychology.

Availability of data and materials

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As Stoddart ( 1990 ) put it: ‘human beings behave as if they are afraid of smelling like human beings, for human beings smell bad’.

To give some sense of the size of the global market for fragranced facial and body products, according to Small and Green ( 2012 ), it was estimated at an impressive US$ 425.8 billion in 2011 alone (see Aikman, 1951 , for a historical perspective; and http://www.leffingwell.com/top_10.htm for more recent figures).

Though, sadly, the Venus de Milo and Mona Lisa were not amongst them. And, what is more, the bespoke scents themselves were only available for sale in the gift shop, and not introduced to the relevant galleries.

In one study, for example, those exposed to a disgusting negative ambient odour (a commercially available ‘fart spray’ comprising hydrogen sulphide and ammonia) gave harsher judgments regarding several types of moral vignettes (for example, sex between first cousins) than those exposed to the control scent (Schnall et al., 2008 ).

Nor is it altogether clear what the participants in the studies considered the relationship between fragrance and visual stimuli to be, or even whether they gave any thought to the matter.

At the same time, however, and as we will see later, odours do not always have to be perceived consciously in order to influence human performance (e.g., Holland et al., 2005 ; Li et al., 2007 ).

A perfume that Paukner ( 1965 ) once memorably described by as being similar to an ‘ideal erogenous perfume’.

Relevant here, both odorants were judged as being equally pleasant, hence ruling out a valence-based explanation for the different pattern of results obtained with the two scents.

This world-famous brand aimed at young men goes by the brand name of Axe in many countries.

The Lynx fragrance and the synthetic body odour scents were both assumed to be more body-relevant to the faces of the young men who were being evaluated that either the smell of geranium and rubber. However, it could be argued that in order for the female participants to code the Lynx fragrance as body-relevant, they would first have needed to recognize the fragrance, presented without any other identifying information, as the smell of a famous young man’s deodorant brand.

The halo effect refers the suggestion that attractive individuals are also considered to have a variety of other positive personal attributes (see also Carragher et al., 2021 ).

It is worth noting that the caramel odour typically takes on innately pleasurable associations with the sweet-taste with which it is normally paired, whereas the aroma of liquorice is more likely to be associated with salty/bitter tastes instead (Stevenson & Boakes, 2004 ).

Note that the liquorice and caramel conditions are mislabelled in Risso et al. ( 2021 , Figure 4), as confirmed by pers. comm. with first author dated May 9th, 2021.

One might even consider what kind of semantic links may be established in the mind of the consumer with a fragrance that happens to be heavily endorsed by a celebrity (Mahdavi et al., 2019 ).

Four male and four female faces, each displaying neutral, happy, and disgusted facial expressions. Using these pictures, 16 unique video clips were created lasting 3 s each. In each video clip, a neutral facial expression developed gradually into either a happy or a disgusted expression. The transformation of faces was therefore not exactly like looking at a natural dynamic face.

Intriguingly, while there were visual-olfactory stimulus combinations that were either congruent (negative-negative) or incongruent (negative-neutral) in terms of their emotion, few, if any, of the combinations could be considered to be semantically congruent, excepting, perhaps, the synthetic BO, fearful face combination.

This consistent with the fact that: ‘perfumes are generally marketed as having the ability to enhance sexual attractiveness’ (Berliner et al., 1991 , p. 671).

Along somewhat similar lines, some commentators have been tempted to suggest that hedonically valenced odours need not modulate facial attractiveness, but might rather affect other affective components of interpersonal perception , for example, perceived sympathy (König, 1972 ).

Note that for various reasons, olfaction (one of the chemical senses) and vision (what Novak et al., 2015 , call a ‘physical’ sense, and Spence, in press, has described as a spatial sense) may potentially show less interaction/confusion.

Speed-dating events might provide an ideal real-world situation to collect some of the relevant data.

Apparently aware of how easily scents could be misattributed, the young men of the French court of centuries gone by would fragrance their apartments in order to try and woo the ladies (Corbin, 1986 , p. 74). Corbin ( 1986 , p. 77) also mentions those who would wear fragranced clothing, with the presumption once again seemingly being that whoever became aware of that fragrance would attribute it to the person rather than their garb. Relevant here, a marketing study by Spangenberg et al. ( 2006 ) highlighted the impact of gender-congruent ambient scent on the on customers’ approach-avoidance behaviours in the context of a clothing retail store. Sometimes, in other words, the gendered scent may be associated with the location, or clothing, rather than necessarily with a particular individual.

In the project Actual Odor, the artist Angela Ellsworth wore a jersey cocktail dress soaked in her own urine for the duration of the opening reception for the Token City installation (a subway simulation) by artist Muriel Magenta at the Arizona State University Art Museum (1997; Drobnick, 2006 ).

Thus contrasting with Graham and Jouhar’s ( 1980 , p. 97) early claim that: ‘All in all, it would appear that sense of smell is fairly unimportant in that we do not rely very much on body odours in their natural form nor is it socially acceptable to emit such body odours. However, the reverse is the case for manufactured odours in the form of perfumes, deodorants or odours indicating cleanliness.’.

Rosebury ( 1969 , p. 208) poses an interesting question: "Maybe we ought to stop at times to wonder why we like flowers or coconuts or little Asiatic deer or the guts of a sperm whale; couldn't we learn to love the smell of healthy sweat of men and women?" Or as Desmond Morris ( 1967 ), puts it in "The Naked Ape": "The female who so assiduously washes off her own biological scent, then proceeds to replace it with commercial 'sexy' perfumes which in reality are no more than diluted forms of the products of the scent glands of other, totally unrelated mammalian species.”

And one should not forget how ‘Napoleon, in one of his more infamous letters to Josephine, begged her not to bathe, for he wanted to enjoy her body odor to the fullest’. (Tanabe, 2004 ).

It should also be noted that some of Dr. Hirsch’s claims regarding the power of olfaction have not gone uncontested in the courts (see Deardorff & King, 2014 ).

For instance, almost a century ago, Herrick ( 1924 ) classified primates in general and human in particular as ‘microsmatic’, on the basis that olfaction played a minor role in their behaviour (though see Schaal & Porter, 1991 , for the contrary position).

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Completion of this review was supported by AHRC ‘Rethinking the Senses’ Grant AH/L007053/1.

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Spence, C. The scent of attraction and the smell of success: crossmodal influences on person perception. Cogn. Research 6 , 46 (2021). https://doi.org/10.1186/s41235-021-00311-3

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Fragrance is used in consumer products around the world. However, fragrance has been associated with adverse effects on indoor and outdoor air quality and human health. Questions arise, such as the following: Why does fragrance in products pose problems? What are sources of emissions and exposures? What are health and societal effects? What are possible solutions? This paper examines the issue of fragranced consumer products and its science and policy dimensions, with a focus on the implications for air quality and human health. Results include new findings and new questions for future research directions.

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Introduction

Fragrance has been used for thousands of years, with the intent to create a more aesthetically pleasing environment and more popular consumer products. However, in recent years, fragrance in products has been associated with adverse effects on air quality and health, despite extensive tests for safety (IFRA 2020a ). What is perplexing is why products designed to be positive may be creating unintended effects.

As background, most of our exposure to pollutants occurs indoors. A primary source of indoor air pollutants is fragranced consumer products, such as air fresheners and cleaning supplies. Further, fragranced products have been implicated as a contributor to outdoor pollutants. However, indoor environments and fragranced product emissions are essentially unregulated. Also, fragranced product ingredients are not required to be fully and specifically disclosed, not on labels, safety data sheets, or elsewhere. Therefore, an important source of air pollutants and exposures is largely unregulated, and the emissions and ingredients are largely unknown. Yet exposures have been associated with a range of health problems, such as breathing difficulties and headaches, in nearly a third of the general population in four countries representing three continents.

This paper analyzes and synthesizes data and research findings on the fragranced products phenomenon. A goal is to provide an integrated understanding of the scientific foundations and policy implications for air quality and health. To do so, it investigates the following questions: How prevalent is product use and exposure? What health problems are associated with exposure? What volatile ingredients are emitted from the products? Are ingredients disclosed? Are green, organic, and natural products any different? What strategies can reduce emissions and exposures? Results point to new insights and new directions for research and, ultimately, new knowledge for understanding and reducing potential effects of fragranced consumer products on air quality and health.

To begin, this paper provides some definitions:

A “fragrance” is a scent and, despite its singular name, it is a formulation of dozens of chemicals, such as volatile organic compounds (VOCs). Nearly 4000 ingredients have been documented for use in the composition of a fragrance (IFRA 2020b ). A fragrance is generally intended to “provide an aroma, to mask an odor, or both” (Steinemann 2019a ).

A “fragranced consumer product” (or “fragranced product” for brevity) is a product that “contains an added fragrance or that is largely comprised of fragrance” (Steinemann 2019a ). Fragranced products cover hundreds of everyday items, such as air fresheners, deodorizers, cleaning supplies, laundry detergents, fabric softeners, essential oils, candles, soaps, personal care products, colognes, and hand sanitizers.

A distinction is made herein between a cosmetic item termed fragrance (such as a perfume or cologne) versus a chemical mixture termed fragrance that is added to a product. This article focuses on the latter, although a fragrance (perfume, cologne) is one of the hundreds of types of fragranced consumer products.

“Fragrance sensitivity” is a health condition characterized by one or more types of adverse health effects from exposure to one or more types of fragranced consumer products (Steinemann 2019b ).

International studies of fragranced consumer products: emissions, exposures, and effects

Nationally representative population-based studies were conducted across four countries—the United States (US), Australia (AU), the United Kingdom (UK), and Sweden (SE)—to investigate fragranced product emissions, exposures, and effects. The studies used cross-sectional surveys of adults ages 18–65, with a questionnaire in the native language as the survey instrument. Sample populations ( n  = 1137, 1098, 1100, 1100, respectively) were representative of the general populations according to age, gender, and region (confidence level = 95%, margin of error = 3% for all studies). Using randomized participant recruitment, the surveys drew upon large web-based panels (with over 5,000,000; 200,000; 900,000; 60,000 participants, respectively). In addition to the general population, the survey also investigated effects on vulnerable sub-populations, such as asthmatic individuals and autistic individuals. The surveys were performed in June 2016 (US, AU, UK) and June 2017 (SE). The survey response rates were 94%, 93%, 97%, and 92% (respectively), and all responses were anonymous. (For additional survey details, see Steinemann 2016 , 2017a , 2018c , d , 2019b .)

The studies investigated the following types of fragrance products, exposures, and effects.

Fragranced products were categorized as follows: “(a) air fresheners and deodorizers (e.g., sprays, solids, oils, disks); (b) personal care products (e.g., soaps, hand sanitizer, lotions, deodorant, sunscreen, shampoos); (c) cleaning supplies (e.g., all-purpose cleaners, disinfectants, dishwashing soap); (d) laundry products (e.g., detergents, fabric softeners, dryer sheets); (e) household products (e.g., scented candles, restroom paper, trash bags, baby products); (f) fragrance (e.g., perfume, cologne, after-shave, essential oils); and (g) other.”

Exposure contexts included the following: “air fresheners or deodorizers used within indoor environments; scented laundry products coming from a dryer vent; being in a room after it was cleaned with scented cleaning products; being near someone wearing a fragranced product; and exposure to other types of fragranced consumer products.”

Health effects were categorized as follows: “(a) migraine headaches; (b) asthma attacks; (c) neurological problems (e.g., dizziness, seizures, head pain, fainting, loss of coordination); (d) respiratory problems (e.g., difficulty breathing, coughing, shortness of breath); (e) skin problems (e.g., rashes, hives, red skin, tingling skin, dermatitis); (f) cognitive problems (e.g., difficulties thinking, concentrating, or remembering); (g) mucosal symptoms (e.g., watery or red eyes, nasal congestion, sneezing); (h) immune system problems (e.g., swollen lymph glands, fever, fatigue); (i) gastrointestinal problems (e.g., nausea, bloating, cramping, diarrhea); (j) cardiovascular problems (e.g., fast or irregular heartbeat, jitteriness, chest discomfort); (k) musculoskeletal problems (e.g., muscle or joint pain, cramps, weakness); and (l) other.”

For fragrance sensitivity, the survey asked, “Do you experience any health problems when exposed to (specific fragranced product or exposure context)?” If the respondent answered yes, the survey then asked the respondent to specify which health problem(s) they experienced. An individual was considered to characterize fragrance sensitivity if they reported one or more types of health problems from exposure to one or more types of fragranced consumer products or exposure contexts.

The study also identified vulnerable populations, such as asthmatic individuals and autistic individuals.

For asthmatic individuals, the survey asked, “Has a doctor or health care professional ever told you that you have asthma or an asthma-like condition?” If the respondent answered yes, the survey then asked to specify which one or both. For this study, “asthmatic individuals” are considered to be medically diagnosed with asthma, an asthma-like condition, or both.

For autistic individuals, the survey asked, “Has a doctor or health care professional ever told you that you have autism or autism spectrum disorder?” If the respondent answered yes, the survey then asked to specify which one or both. For this study, “autistic individuals” are considered to be medically diagnosed with autism, an autism spectrum disorder, or both.

Results are provided below, with averages across the countries provided as single percentage, and with individual country results (US, AU, UK, SE) provided as a series of four percentages, respectively. Complete results with data and statistics, for each country, each sup-population, and each question, are provided in Steinemann ( 2016 , 2017a , 2018a , b , c , d , 2019a , b , c ).

Pervasiveness of product use and exposure

Fragranced consumer products are used around the world. Exposure is common, both direct and indirect, voluntary and involuntary.

Across the four countries, 99.1% of the population is exposed to fragranced products, at least once a week, from their own use (98.3%), from others’ use (90.6%), or from either or both (99.1%). For individual countries: from own use (98.3%, 98.0%, 98.5%, 98.5%), from others’ use (92.1%, 88.1%, 89.0%, 93.3%), or from either or both (99.0%, 98.5%, 99.3%, 99.5%).

Specific product results, for population exposure at least once a week, are as follows: air fresheners and deodorizers, 74.7%; personal care products, 93.2%; cleaning supplies, 86.2%; laundry products, 87.1%; household products, 79.1%; fragrance, 82.8%; and other products, 3.7%.

The problem of widespread exposure (90.6%) to others’ use of products gives rise to the problem of “secondhand scents”: indirect or involuntary exposure to fragranced products (Steinemann 2019a ). Consequences of secondhand scents include, for example, restricted access in society, health risks, lost workdays and lost jobs, and negative effects in daily life and living situations.

Prevalence of fragrance sensitivity

Among the general population, across the four countries, 32.2% of adults on average (34.7%, 33.0%, 27.8%, 33.1%) report fragrance sensitivity; that is, adverse health effects from exposure to fragranced consumer products.

Among vulnerable sub-populations, the prevalence of fragrance sensitivity is higher. For instance, 57.8% of asthmatic individuals and 75.8% of autistic individuals report adverse effects from fragranced products.

Fragranced product exposures

Fragranced product exposures, with associated frequencies of reports of health problems, include but are not limited to the following:

General population: air fresheners and deodorizers, 17.4% (20.4%, 16.4%, 15.5%, 17.3%); fragranced laundry products coming from a dryer vent, 7.6% (12.5%, 6.1%, 6.0%, 5.6%); being in a room after it has been cleaned with fragranced products, 15.7% (19.7%, 15.3%, 14.0%, 13.8%); being near someone who is wearing a fragranced product, 20.1% (23.6%, 19.4%, 13.7%, 23.5%); and other types of fragranced consumer products, 18.6% (22.3%, 20.3%, 13.9%, 17.9%).

For vulnerable sub-populations, the exposures and associated frequencies of reports of health problems (% relative to each sub-population) include the following:

Asthmatic individuals: air fresheners and deodorizers (36.7%), fragranced laundry products coming from a dryer vent (18.1%), being in a room after it has been cleaned with fragranced products (32.9%), being near someone who is wearing a fragranced product (38.7%), and other types of fragranced consumer products (37.5%).

Autistic individuals: air fresheners and deodorizers (62.9%), fragranced laundry products coming from a dryer vent (57.5%), being in a room after it has been cleaned with fragranced products (65.9%), being near someone who is wearing a fragranced product (60.5%), and other types of fragranced consumer products (64.3%).

Vulnerable sub-populations have a higher frequency of reports of health problems than the general population, across all exposure contexts. For instance, when exposed to air fresheners or deodorizers, 36.7% of asthmatic individuals and 62.9% autistic individuals report health problems, compared with 17.4% of the general population.

Each of these exposure contexts represents a potentially involuntary exposure, and one that can pose risks to an individual’s health and their ability to have access and opportunities in society. Further, all types of fragranced products and exposure contexts studied were associated with adverse health effects.

Health problems

Across the general population in the four countries, the frequency and types of adverse health effects associated with fragranced product exposures include the following: respiratory problems, 16.7% (18.6%, 16.7%, 11.6%, 20.0%); mucosal symptoms, 13.2% (16.2%, 14.0%, 9.2%, 13.5%); migraine headaches, 12.6% (15.7% 10.0% 8.4% 16.1%); skin problems, 9.1% (10.6% 9.5% 9.8% 6.5%); asthma attacks, 7.0% (8.0% 7.6% 6.8% 5.5%); neurological problems, 5.1% (7.2% 4.5% 3.7% 5.0%); cognitive problems, 4.3% (5.8% 4.1% 2.8% 4.5%); gastrointestinal problems, 3.8% (5.5% 3.3% 3.0% 3.5%); cardiovascular problems, 3.2% (4.4% 3.0% 3.2% 2.1%); immune system problems, 2.7% (4.0% 3.3% 1.9% 1.5%); musculoskeletal problems, 2.5% (3.8% 2.6% 2.0% 1.5%); and other, 2.0% (1.7% 1.9% 2.1% 2.2%).

For vulnerable sub-populations, the frequencies of the types of adverse health effects (% relative to that sub-population) include the following:

For asthmatic individuals: respiratory problems (37.7%), mucosal symptoms (25.4%), asthma attacks (25.0%), migraine headaches (22.6%), skin problems (17.1%), neurological problems (10.2%), cognitive problems (9.8%), gastrointestinal problems (8.6%), cardiovascular problems (7.9%), immune system problems (6.5%), musculoskeletal problems (6.5%), other (1.6%).

For autistic individuals: respiratory problems (44.7%), migraine headaches (42.9%), mucosal symptoms (42.1%), skin problems (39.7%), asthma attacks (35.9%), cardiovascular problems (34.3%), neurological problems (34.3%), musculoskeletal problems (34.1%), cognitive problems (32.5%), gastrointestinal problems (29.2%), immune system problems (31.4%), and other (2.0%).

Thus, across the general population and each of the vulnerable sub-populations, the most frequently reported adverse health effects are respiratory problems, mucosal symptoms, migraine headaches, skin problems, and asthma attacks.

For each type of health problem, the frequencies are higher for vulnerable sub-populations. For instance, respiratory problems are reported by 37.7% of asthmatic individuals and 44.7% of autistic individuals when exposed to fragranced products, compared with 16.7% of the general population (Steinemann and Goodman 2019 ; Steinemann et al. 2018 ; Steinemann 2018a , b ). Also, migraine headaches are reported by 22.6% of asthmatic individuals and 42.9% of autistic individuals when exposed to fragranced products, compared with 12.6% of the general population (Steinemann and Nematollahi 2020 ; Steinemann 2018a , b ).

Disabling health effects

Health effects from exposure to fragranced products can be so severe as to be considered disabling, according to legislative criteria for disability in each country. Across the four countries, 9.5% of the general population (17.2%, 5.6%, 7.1%, 8.0%), representing 29.1% of fragrance sensitive individuals (49.5%, 17.1%, 25.5%, 24.2%), report health effects that could be considered disabling, according to the disability legislation in each country (ADAAA 2008 ; DDA 1992 ; EA 2010 ; DA 2008 ).

For vulnerable individuals, percentages of disabling effects are higher. For 24.1% of asthmatic individuals (40.3%, 15.0%, 20.1%, 20.8%) and 72.8% of autistic individuals (85.4%, 82.4%, 54.5%, 69.0%), health problems from fragranced products can be potentially disabling.

Loss of workdays and loss of jobs

Among the general population across the four countries, 9.0% of adults have lost workdays or lost a job, in the previous year, due to illness from fragranced product exposure in the workplace (15.1%, 7.7%, 6.3%, 6.7%). For vulnerable individuals, the percentages are higher: 20.6% of asthmatic individuals and 59.4% of autistic individuals have lost workdays or lost a job, in the past year, due to fragranced product exposure in the workplace. (Steinemann 2019b .)

Personal costs due to these lost workdays and lost jobs, in the past year, ranged from an estimated $86 billion to $206 billion, with a midrange value of $146 billion (in terms of 2016 USD). Losses estimated for each country (US, AU, UK, SE) are as follows (midrange value, 2016 USD): $132 billion, $2.7 billion, $10.5 billion, $900 million. (Steinemann 2019b .)

Given the population of 33.9 million people who have lost workdays or a job due to fragranced product exposure (30.2 million, 1.1 million, 2.2 million, 0.4 million), this represents an average annual cost of $4300 USD per person. Costs are estimated for direct personal expenses only and do not include other costs to individuals, employers, the health care system, and the broader society, associated with loss of productivity and loss of employment. (Steinemann 2019a , b .)

Loss of societal access

Fragranced product exposures, or the potential for exposures, are associated with loss of societal access:

Among the general population across the countries: 13.3% of individuals (17.5%, 11.6%, 12.1%, 12.0%) are unable or reluctant to use the restrooms in a public place, because of the presence of an air freshener, deodorizer, or scented product; 10.4% of individuals (14.1%, 10.3%, 10.3%, 6.7%) are unable or reluctant to wash their hands with soap in a public place, because the soap is fragranced; 17.0% of individuals (20.1%, 16.7%, 13.1%, 8.1%) report that if they enter a business, and smell air fresheners or some fragranced product, they want to leave as quickly as possible; and 16.0% of individuals (22.7%, 15.0%, 13.5%, 12.6%) have been prevented from going to some place because they would be exposed to a fragranced product that would make them sick.

For vulnerable sub-populations: 26.4% of asthmatic individuals and 62.1% of autistic individuals are unable or reluctant to use the restrooms in a public place, because of the presence of an air freshener, deodorizer, or scented product; 21.9% of asthmatic individuals and 59.8% of autistic individuals are unable or reluctant to wash their hands with soap in a public place, because the soap is fragranced; 31.6% of asthmatic individuals and 58.7% of autistic individuals report that if they enter a business, and smell air fresheners or some fragranced product, they want to leave as quickly as possible; and 32.9% of asthmatic individuals and 66.7% of autistic individuals have been prevented from going to some place because they would be exposed to a fragranced product that would make them sick.

Across all types of exposures, the percentages of individuals adversely affected are higher for vulnerable sub-populations. Practical implications of the results are compelling. For instance, more than one-fourth of asthmatic individuals and one-half of autistic individuals are prevented from using public restrooms that have air fresheners. Although washing hands with soap is intended to reduce health risks, individuals may be prevented from washing hands with soap due to health risks associated with fragrance in the soap. Further, a store using an air freshener or fragranced product may actually turn away rather than attract customers.

Product emissions as air pollutants

Fragranced consumer products can be a primary source of indoor air pollutants (Steinemann 2017b ). In studies of indoor environments around the world, fragranced product chemicals (such as limonene) are consistently among the most prevalent and highest concentrations among pollutants (e.g., Goodman et al. 2017 ; Jia et al. 2008 ; Wang et al. 2017 ). In addition to being a primary source of indoor pollutants, fragranced products have been implicated as major contributors to outdoor air pollution (e.g., McDonald et al. 2018 ). Thus, in an interesting development, fragranced consumer products used indoors have received regulatory attention because of the ability of product emissions to migrate outdoors and affect ambient air quality (CARB 2019 ).

Product ingredients and disclosure

Ingredients in fragranced consumer products are not required to be specifically and fully disclosed, in any country (Lunny et al. 2017 ; Steinemann 2015 , 2009 ; Steinemann et al. 2011 ). Main components of the regulations are as follows:

No law in any country requires the full disclosure of all ingredients in a chemical mixture termed “fragrance,” not on the product label, safety data sheet, or elsewhere. Instead, a product may list the general term “fragrance” (or another legally approved term, such as “perfume” or “parfum”) instead of listing all individual ingredients in that fragrance.

No law requires that consumer products (i.e., products other than foods, drugs, and cosmetics) disclose all ingredients on the label, safety data sheet, or elsewhere. Further, these products are not even required to list the general term “fragrance.”

For the other classes of consumer products (i.e., foods, drugs, and cosmetics), while they do need to list all ingredients on the label (although not on the safety data sheet), the general term “fragrance” may be used instead of the specific ingredients.

Thus, and paradoxically, a primary source of exposure to pollutants, fragranced consumer products, is exempt from full disclosure of the ingredients that contribute to the pollutants. Consequently, the public, professionals, and agencies lack information to understand the links between emissions, exposures, and effects on air quality and health.

Volatile emissions from fragranced consumer products

Notwithstanding the regulatory protections on full ingredient disclosure, products can be chemically analyzed to determine their constituents. A set of studies analyzed volatile organic compounds (VOCs) emitted from common consumer products, both fragranced and fragrance-free versions, and green and regular versions (Steinemann 2015 ; Nematollahi et al. 2018a , b , 2019 ; Steinemann et al. 2020 ). Products were randomly selected from stores in the US and AU, although the same or similar products are also available internationally. Product definitions for these studies are as follows:

“Fragranced products” are considered products that contain “fragrance,” “parfum,” “perfume,” “essential oils,” or an aromatic scent (even if undisclosed). “Fragrance-free” products are considered products with the claim of “fragrance-free” or “no fragrance.” (To note, “unscented” products are not included in this category, because they may actually contain a fragrance to cover the scent.)

“Green products” are considered products with the claim of “green” or a related term such as “organic,” “natural,” “no petrochemicals,” “certified green,” “certified organic,” or “essential oils” for the entire product or specific ingredients. “Regular products” are the products other than those in the “green” category.

The studies used gas chromatography/mass spectrometry (GC/MS) headspace analysis to identify the VOCs emitted directly from each product. The top 20 peaks (highest concentration compounds) for each product were identified from the sample chromatogram using mass spectral library matches. Further analytic details are provided in Steinemann et al. ( 2011 ) and Nematollahi et al. ( 2018a ).

“VOC occurrences” refers to the collective number of individual VOCs or ingredients emitted from the products. “VOC identities” refers to the number of distinctly named VOCs emitted from one or more of the products.

Main results of five studies (Steinemann 2015 ; Nematollahi et al. 2019 , 2018a , b ; Steinemann et al. 2020 ) are provided respectively below.

Study of 37 common consumer products: air fresheners, laundry products, cleaning supplies, and personal care products. The GC/MS analyses found 559 VOC occurrences, representing 156 VOC identities. Among these VOCs, 230 VOC occurrences, representing 42 VOC identities, are classified as potentially hazardous. All products emitted potentially hazardous VOCs.

The most common fragranced product VOCs (> 80% of products) were limonene and beta-pinene. The most common fragrance-free product VOC (100% of products) was ethanol, which was also in fragranced products. The most common potentially hazardous VOCs (> 75% of products) were ethanol and limonene. No significant difference was found in the emissions of hazardous air pollutants between green fragranced products and regular fragranced products.

Fewer than 3% of the VOCs, and fewer than 6% of potentially hazardous VOCs, were disclosed on the product labels, safety data sheets, or elsewhere. Further, among the fragranced consumer products (other than cosmetics), 91% did not disclose the presence of a “fragrance” on the label or safety data sheet. Among the fragranced cosmetics, 89% did not disclose “fragrance” on the safety data sheet, but all disclosed “fragrance” on the label, as required.

Study of 134 common consumer products: air fresheners, laundry products, cleaning supplies, personal care products, and sunscreens. The GC/MS analyses found 1538 VOC occurrences, representing 338 VOC identities. Among these VOCs, 517 VOC occurrences, representing 69 VOC identities, are classified as potentially hazardous. Nearly all products (99%) emitted potentially hazardous VOCs.

The most common fragranced product VOC (77% of products) was limonene. The most common fragrance-free product VOC (40% of products) was ethanol. The most common potentially hazardous VOCs (> 40% of products) were limonene and ethanol. No significant difference was found in emissions of the most prevalent potentially hazardous VOCs between green fragranced products and regular fragranced products.

Fewer than 10% of VOCs, and fewer than 4% of potentially hazardous VOCs, were disclosed on the product labels, safety data sheets, or elsewhere.

Study of 42 fragranced baby products: shampoos, lotions, hair sprays, and fragrance. The GC/MS analyses found 684 VOC occurrences, representing 228 VOC identities. Among these VOCs, 207 VOC occurrences, representing 43 VOC identities, are classified as potentially hazardous.

The most common fragranced baby product VOC (67% of products) was limonene. The most common potentially hazardous VOCs (> 55% of products) were limonene, acetaldehyde, and ethanol. No significant difference was found in the emissions of the most prevalent potentially hazardous VOCs between green fragranced baby products and regular fragranced baby products.

Fewer than 5% of VOCs, and fewer than 13% of potentially hazardous VOCs, were disclosed on the product labels, safety data sheets, or elsewhere.

Study of 24 commercial essential oils. The GC/MS analyses found 589 VOC occurrences, representing 188 VOC identities. Among these VOCs, 124 VOC occurrences, representing 33 VOC identities, are classified as potentially hazardous.

The most common essential oil VOCs (> 70% of oils) were alpha-pinene, limonene, and acetone. The most common potentially hazardous VOCs (> 70% of oils) were limonene and acetone. No significant difference was found in the emissions of the most prevalent potentially hazardous VOCs between natural and regular essential oils. No ingredients were disclosed on any of the essential oil labels.

Study of 12 car air fresheners. The GC/MS analyses found 546 VOC occurrences, representing 275 VOC identities. Among these VOCs, 30 VOC occurrences, representing 9 VOC identities, are classified as potentially hazardous.

The most common car air freshener VOCs (> 70% of products) were limonene, benzyl acetate, acetone, and ethanol. The most common potentially hazardous VOCs (67% of products) were acetaldehyde and methanol. No significant difference was found in the emissions of the most prevalent potentially hazardous VOCs between green and regular car air fresheners. Fewer than 2% of VOCs, and none of the potentially hazardous VOCs, were disclosed on the product labels, safety data sheets, or elsewhere.

Most prevalent VOCs

Across the five studies, the 249 products emitted collectively 3916 VOCs. The most prevalent compounds in fragranced products were terpenes (limonene, alpha-pinene, beta-pinene), which were not found in fragrance-free products. The most prevalent compound in fragrance-free products was ethanol, which was also a common compound in fragranced products.

Potentially hazardous VOCs

Across the studies, the 249 products emitted collectively 1108 potentially hazardous VOCs, which represents 28% of all VOC occurrences. Nearly all products (99%) emitted potentially hazardous VOCs. The most prevalent potentially hazardous VOCs were limonene (67% of products), ethanol (53%), and acetaldehyde (44%).

Comparing VOCs emitted and ingredients listed

Across the studies, on average, fewer than 4% of all VOCs, and fewer than 5% of potentially hazardous VOCs, were disclosed on any product label, safety data sheet, or elsewhere.

Comparing green fragranced products and regular fragranced products

Also, across the studies, no significant difference was found in the emissions of the most prevalent potentially hazardous VOCs between green (organic, natural) fragranced products and regular fragranced products.

Comparing fragranced and fragrance-free products

Across all studies, comparing emissions from fragranced and fragrance-free versions of the same types of products, the main chemical difference is the presence of terpenes (such as limonene, beta-pinene, and alpha-pinene) in all fragranced products, and the absence of terpenes in all fragrance-free products. This leads to a focus on terpenes.

Terpenes and reaction products

Terpenes were the most commonly and consistently emitted VOCs from fragranced products. As noted above, terpenes were present in all fragranced products tested, but absent in all fragrance-free products tested.

Terpenes characteristic of fragranced consumer products are among the most abundant pollutant indoors and they contribute to pollutants outdoors (Steinemann et al. 2013 ; Steinemann 2015 ). In addition to being primary emissions, terpenes react with other chemicals to generate a range of secondary and potentially hazardous pollutants. For instance, terpenes react with ozone indoors to generate pollutants such as formaldehyde and ultrafine particles (Nazaroff and Weschler 2004 ). Terpenes react with nitrogen oxides outdoors to generate ozone and secondary organic aerosols (McDonald et al. 2018 ).

Common terpenes in the fragranced consumer products, such as limonene, are chiral molecules: they can exist as a right-hand enantiomer (e.g., d-limonene), a left-hand enantiomer (e.g., l-limonene), or a mixture. Chiral molecules found in nature are usually and predominantly one enantiomer or another, whereas chiral molecules that are synthetized are usually a mixture of enantiomers. For a specific chiral molecule, individual enantiomers and their mixtures can have the same chemical structure but different biological effects. An interesting area for scientific exploration is the potential difference in effects of different enantiomeric forms and sources of chiral fragrance molecules.

The paper now turns to promising approaches to reduce emissions, exposures, and effects.

Fragrance-free products

Fragrance-free products can offer similar functionality but without the potential issues associated with fragranced products. For instance, a cleaning or disinfection product may be similarly effective at its primary function without the added fragrance. Further, changes from fragranced to fragrance-free products can reduce terpenes emissions in a relatively short time period. For instance, changing from fragranced to fragrance-free laundry products can reduce concentrations of fragrance chemicals (i.e., limonene) emitted from dryer vents by up to 99% within 4 weeks (Goodman et al. 2019b ). While the term “fragrance-free products” is not intended to imply emissions-free products, they do offer an option for consumer product functionality without the fragrance compounds.

In addition, removing or discontinuing use of fragrance products can also reduce emissions and exposures. For instance, removing or turning off air fresheners in a restroom can reduce concentrations of fragrance chemicals within indoor environments by up to 96% within 2 weeks (Goodman et al. 2019a ). Because fragrance molecules can adhere to surfaces during product use and be re-emitted later, even without the product in use, reduction may not be 100% immediately, but fragrance compound concentrations can decrease with time.

Moreover, the fact that fragranced products can constitute a barrier to participation in society can come under the auspices of disability legislation. The change to a fragrance-free product, the removal of the fragranced product, or a modification in facilities or operations to mitigate fragrance exposure, for instance, could be considered forms of reasonable accommodation. To this end, fragrance-free practices and policies have been implemented across the countries to accommodate sensitive and vulnerable individuals, as well as to reduce potential health risks and create a more healthful indoor air environment for all (Steinemann 2019a ).

Preferences for fragrance-free policies and fragrance-free environments

Nationally representative population surveys, across the four countries (US, AU, UK, SE), found that more people, at least twice as many, prefer fragrance-free environments to fragranced environments, such as workplaces, health care facilities and professionals, hotels, and airplanes. Among vulnerable sub-populations, preferences for fragrance-free environments are even higher. Interestingly, even among individuals who do not report fragrance sensitivity, a majority of these non-fragrance sensitive individuals would nonetheless prefer fragrance-free environments. Specific results are as follows (Steinemann 2018a , b , 2019a , b .)

For workplaces: 47.8% (53.1%, 42.8%, 44.7%, 50.7%) of the general population would support a fragrance-free policy in the workplace, compared with 20.4% (19.7%, 22.2%, 23.3%, 6.4%) that would not. Also, 56.7% of asthmatic individuals would support fragrance-free workplace policies, compared with 17.7% that would not; 65.5% of autistic individuals would support fragrance-free workplace policies, compared with 24.0% that would not; and 40.4% of non-fragrance sensitive individuals would support fragrance-free workplace policies, compared with 23.4% that would not. Thus, more than twice as many individuals would support (than would not) fragrance-free policies in workplaces.

For health care: 51.4% (54.8%, 43.2%, 43.3%, 64.1%) of the general population would prefer that health care facilities and health care professionals be fragrance-free, compared with 22.1% (22.4%, 25.2%, 26.7%, 14.0%) that would not. Also, 62.3% of asthmatic individuals would prefer fragrance-free health care, compared with 18.3% that would not; 77.2% of autistic individuals would prefer fragrance-free health care, compared with 16.4% that would not; and 42.3% of non-fragrance sensitive individuals would prefer fragrance-free health care, compared with 26.3% that would not. Thus, more than twice as many individuals would support (than would not) fragrance-free health care facilities and fragrance-free health care professionals.

For hotels: 60.7% (55.6%, 55.6%, 53.8%, 77.7%) of the general population would prefer hotels without fragranced air, compared with 22.1% (27.8%, 22.7%, 28.1%, 9.8%) with fragranced air. Also, 65.8% of asthmatic individuals would prefer hotels without fragranced air, compared with 22.7% with fragranced air; 52.1% of autistic individuals would prefer hotels without fragranced air, compared with 38.1% with fragranced air; and 53.7% of non-fragrance sensitive individuals would prefer hotels without fragranced air, compared with 25.1% with fragranced air. Thus, more than twice as many individuals would prefer hotels without fragranced air than with fragranced air.

For airplanes: 64.8% of the general population would prefer airplanes without fragranced air, compared with 16.1% (59.2%, 57.7%, 61.9%, 80.2%) with fragranced air. Also, 68.8% of asthmatic individuals would prefer airplanes without fragranced air, compared with 17.3% with fragranced air; 48.4% of autistic individuals would prefer airplanes without fragranced air, compared with 41.2% with fragranced air; and 59.5% of non-fragrance sensitive individuals would prefer airplanes without fragranced air, compared with 17.3% with fragranced air. Thus, more than twice as many individuals would prefer airplanes without fragranced air than with fragranced air.

In summary, across all settings (workplaces, health care facilities and health care professionals, hotels, and airplanes), more than twice as people prefer fragrance-free to fragranced environments. Even a majority of individuals who do not report fragrance sensitivity would nonetheless prefer fragrance-free environments. These findings are juxtaposed with trends of putting fragranced air through indoor environments, even at potential risks to individuals who can experience severe health effects from exposure.

Future research

This fragrance phenomenon is a puzzle, and this article sought to investigate the pieces and bring them together to provide new insights and directions. This domain also provides a rich area for research. Future questions for exploration include the following:

What chemicals or mixtures of chemicals could be associated with the reported adverse effects?

What are possible differences in effects between different forms (enantiomeric compositions) and different sources (natural, synthesized) of chiral terpenes as found in products?

How can specific sources of fragrance chemicals that affect indoor and outdoor air quality and health, such as fragranced laundry products emitted from dryer vents, be mitigated or regulated?

What policies or laws can help protect individuals affected by fragranced products from involuntary exposures, health risks, and loss of societal access due to secondhand scents?

What are relative benefits for air quality and health of implementing fragrance-free policies?

Given that fragrance formulations are extensively tested for safety, yet fragrance is associated with reports of adverse health effects, how and why could this occur?

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Acknowledgments

I deeply thank John Barrie, Nigel Goodman, and Neda Nematollahi for their exceptionally thoughtful and helpful reviews of the paper. I also thank Dynata (Survey Sampling International) for their superb work on the surveys. I greatly appreciate the anonymous reviewers of this paper. Finally, this article is written as a tribute and with gratitude to the Founder, Emeritus Editor-in-Chief, Professor Yong S. Chung, who selflessly devoted his life to this journal, and helped to improve air quality, atmosphere, and health around the world.

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Steinemann, A. The fragranced products phenomenon: air quality and health, science and policy. Air Qual Atmos Health 14 , 235–243 (2021). https://doi.org/10.1007/s11869-020-00928-1

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Research Article

Social success of perfumes

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Resources, Software, Visualization, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliation Theoretical Physics Group and Centre for Complexity Science, Imperial College London, Department of Physics, London, United Kingdom

Roles Conceptualization, Investigation, Methodology, Supervision, Writing – original draft, Writing – review & editing

• Vaiva Vasiliauskaite, 
• Tim S. Evans

• Published: July 3, 2019
• https://doi.org/10.1371/journal.pone.0218664
• Reader Comments

After this article [ 1 ] was published, questions were raised about the dataset used in the study. In following up on these questions it came to light that the dataset was obtained from a third-party commercial entity whose identity cannot be shared due to a nondisclosure agreement, and that the authors cannot share the raw data or provide clarifications about how the data were collected or processed. The authors posted anonymized summary data on Figshare, as noted in the article’s Data Availability Statement. However, the reported Methods are not sufficient to enable other researchers to reproduce the study and the data provided do not meet PLOS ONE ’s requirements as outlined in our Data Availability policy. The authors noted that they cannot reproduce the analyses using another public dataset as no comparable dataset is currently available.

In light of these issues, the PLOS ONE Editors retract this article due to concerns about the reproducibility of the study and noncompliance with the journal’s Data Availability policy. We regret that these issues were not identified prior to the article’s publication.

VV and TSE agreed with retraction.

10 Sep 2019: The PLOS ONE Editors (2019) Retraction: Social success of perfumes. PLOS ONE 14(9): e0222524. https://doi.org/10.1371/journal.pone.0222524 View retraction

We study data on perfumes and their odour descriptors—notes—to understand how note compositions, called accords, influence successful fragrance formulas. We obtain accords which tend to be present in perfumes that receive significantly more customer ratings. Our findings show that the most popular notes and the most over-represented accords are different to those that have the strongest effect to the perfume ratings. We also used network centrality to understand which notes have the highest potential to enhance note compositions. We find that large degree notes, such as musk and vanilla as well as generically-named notes, e.g. floral notes , are amongst the notes that enhance accords the most. This work presents a framework which would be a timely tool for perfumers to explore a multidimensional space of scent compositions.

Citation: Vasiliauskaite V, Evans TS (2019) Social success of perfumes. PLoS ONE 14(7): e0218664. https://doi.org/10.1371/journal.pone.0218664

Editor: Yongli Li, Harbin Institute of Technology, CHINA

Received: November 30, 2018; Accepted: June 6, 2019; Published: July 3, 2019

Copyright: © 2019 Vasiliauskaite, Evans. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: Data, supporting the results are available from Figshare (DOI: 10.6084/m9.figshare.7218734 ).

Funding: V.V. acknowledges support from EPSRC, grant number EP-R512540-1. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Smell is a cultural and social phenomenon. People (alongside other animals) bond over smell and associate odours perceived with certain memories [ 1 , 2 ]. In some cultures, smell is so important that there are more adjectives to describe smells than there are for sights or sounds [ 3 , 4 ]. Smell is an often undervalued yet potent emotional stimulant. Patrick Süskind in his book “Perfume: The Story of a Murderer” captivates not only with an engrossing story line but also with a power of smell over a man. The empowerment is well described in the following quote: “Odors have a power of persuasion stronger than that of words, appearances, emotions, or will. The persuasive power of an odor cannot be fended off, it enters into us like breath into our lungs, it fills us up, imbues us totally. There is no remedy for it.” [ 5 ]

In this work, we are interested in an artistic branch of olfaction—perfumery. Perfumery is the act of combining different olfactory ingredients, naturally occurring oils and chemical molecules, into a harmonious aromatic whole—a perfume. For as long as records of perfumery have been kept, the first dating back to Mesopotamian times [ 2 ], the work of composing perfumes has been a job for “the Nose”—an expert with the knowledge of pairwise complementary scent ingredients, their volatilities, odour longevities and other aspects that play role in perfume making. This expertise is typically acquired over many years of training and trials of many different combinations of ingredients. This study explores the potential of on-line data to inform the art of perfumery by providing insights about the combinations of ingredients that lead to the most successful fragrance formulas.

A perfume is an exact chemical formula, developed by the Nose using his/hers years of experience of trial and error of multitudes of ingredient combinations. Each perfume constitutes of a specific combination of essential oils, which results in a unique scent of the perfume. It is then diluted with alcohol to result in cologne , eau de perfume or eau de toilette .

Perfumes are often described using notes . Notes are descriptors of scents that can be sensed upon the application of a perfume. Compositions of several notes, in particular the popular compositions that occur in many different perfumes, are called accords (from the French for a musical chord ).

To create a well-balanced aromatic mixture, a variety of different smells are combined, so notes in a perfume are often varied and diverse. It is thought that a well-balanced perfume should comprise of ingredients with a wider range of volatilities: it should include some ingredients which evaporate quickly as well as those which linger for longer. This idea leads to a classification of notes into one of three types: base notes (least volatile), heart notes (average volatility) and top notes (most volatile) [ 6 ].

Information of the precise amounts of each ingredient in the formulation of a perfume is confidential, to prevent duplications of the formula. However, the list of ingredients, the list of notes, is often advertised in order to describe the scent of a perfume. Thus a perfume which smells of rose, vanilla and musk, is described using such notes. In this study we have analysed the notes which make up over ten thousand perfumes without knowing anything about their specific amounts in each perfume. We assume that a note is included in the perfume description as its presence enriches the composition and its smell is detectable.

Most of the research on fragrances concerns biological and chemical features of olfaction [ 7 ] and economics of perfume industry [ 8 ]. Studies of human response to smell, such as how odours affect performance of certain tasks or mood have been conducted as well [ 9 – 11 ]. Olfaction is also part of the sense of flavour, alongside taste. Many studies explored how loss of smell influences the ability to sense flavours, for example see [ 12 ] and references therein.

In our work, we study perfumes and their constituent notes as a complex network. Data driven approaches to market research and consumer trend analysis, for perfumes in particular, are now common. For instance, artificial neural networks are now widely used in business and marketing where in the context of perfumes they have been used to identify customer requirements and to recommend future purchases to customers [ 13 ]. However, perfume-note data has not been studied as a complex network. There are similarities with the analysis or food recipe networks [ 14 – 16 ], networks of flavour compounds [ 17 – 19 ] and drug prescriptions [ 20 ] as well as analysis of social media, such as Twitter [ 21 ], concerning recipes.

Our work shows that our data on perfumes provides useful insights into the factors that are influential, and those which are not, when creating a successful product in the fragrance industry. We use positive and prolific customer feedback as out measure of success. We analyse multiple factors that could affect the observed success of a perfume: its launch date, popularity of its brand, price and ingredients. We compare potential success factors to popularity of perfumes as seen in an online database of perfumes.

We will assume that a large number of votes for a perfume is a measure of its success. This is a common assumption of most rating systems since in most cases voters leave positive feedback rather than criticise a product (for example see [ 22 , 23 ] especially the references and values in Table 30.1 of the latter). In reality, there may be great perfumes that will never be highlighted as very popular. They may cater very well a small clientele, but not appeal to others due to their price, specificity or other factors. To account for this effect, we would need a much richer dataset that would include information about individuals reviewing the fragrances. So in our study we assume that the larger the number of votes for a perfume, the more successful that perfume is which will inevitably penalise some great perfumes that are not universally popular.

Materials and methods

We have information on 1047 different notes present in 10,599 perfumes. Users can provide a rating for each perfume and for each perfume p we have the number of such ‘votes’, V p , and the average rating R p . In addition the same web site also provided information about first year of production of each perfume. We also found prices for 978 of these perfumes since not all our perfumes are in production at the moment. In this study we consider prices in British Pounds per 100ml.

Our dataset required some cleaning. Some notes carried very similar names and we deemed these to synonyms for the same note. These differences could be due to spelling mistakes, the use of different languages or conventions. For instance, Vanilla (English) or Vanille (French) refer to the same note. In such cases, we would identify the two notes as identical and replace, for instance, all Vanille occurrences with Vanilla . Another complication is that there may be notes with similar names whose odour profiles are distinct. For instance, our dataset contains Vanilla , Tahitian Vanilla and Mexican Vanilla , and the origin of an ingredient may determine its odour profile. We chose not to alter names of such special notes.

After this tidying, we were left with 990 notes, see [ 24 ] for further information.

An example of this network representation is given in Fig 1 .

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• PNG larger image
• TIFF original image

An edge (black lines) is drawn between a perfume (a black dot with the perfume shown above it) and a note (large grey dots with names) only if that note features in the given perfume’s composition.

https://doi.org/10.1371/journal.pone.0218664.g001

Woody Notes are enhancing a composition of raspberry , citruses and lavender . The last three notes feature in both “Fuel for Life” and “Lavanda” however, “Fuel for Life” has an additional woody notes note and a higher number of reviews. Thus woody notes must be enhancing the composition of raspberry , citruses and lavender .

https://doi.org/10.1371/journal.pone.0218664.g002

We know of no other one-mode projection network which defines edges as in our enhancement network. Standard methods, such as those used in the context of other types of recipe, e.g. [ 17 ], produce networks where edges are always reciprocated if not exactly symmetric, see [ 25 ] for an overview. By removing one set of nodes, any one-node projection of a bipartite network will always lose some information. Likewise, by focussing on a relationships of pairs of notes, rather than a more complicated hypergraph representation, we may not encode all the relevant information available. However our aim with our enhancement network is to produce a representation of our data on perfumes which highlights key features while hiding aspects which are of little relevance. In particular, our use of metadata, here in the form of the votes, is designed to bring out important aspects of the data. A more detailed definition and a discussion on possible variations of our enhancement network is given in the Supplementary Information.

Non-network results

One measure of the impact or importance of a perfume is the number of reviews it has received, V p . We find that the distribution of the number of reviews of perfumes is fat-tailed. That is only a handful of perfumes receive a high number of reviews whereas the majority of perfumes receive little attention, see Fig 3 . Such fat-tailed distributions in the popularity of similar objects are common as the degree distribution visualisations of the many data sets in the Konect Project [ 26 ] illustrate. Using the number of reviews for each perfume, V p , as a measure of their significance we find the top five to be, from largest to smallest V p : “Light Blue” (D&G), “J‘adore” (Dior), “Euphoria” (Calvin Klein), “N°5” (Chanel), and “Chloe” (Chloe).

The real distribution of ratings (blue crosses) follows a fat-tailed distribution. The red circles show a logarithmically binned probability distribution which acts as a guide of eye to see that there are just a few perfumes which receive a large number of reviews.

https://doi.org/10.1371/journal.pone.0218664.g003

On the other hand, the rating given by reviewers for any perfume is bounded (between 0 and 5) and the average rating value we have, R p , is based on a sum of these values. So naturally, the distribution of these rating values is not fat tailed and they are typically clustered between 3.5 and 4.0 as is clear in Fig 4 . Clustering of ratings at high values is a common feature of ratings, for example see [ 27 ], since most ratings are positive [ 22 , 23 ].

Panels A, B show that the majority of older perfumes (launched before 1970s) have a relatively large normalised average score W , whereas there is a much larger variation in scores acquired for perfumes launched more recently. Panels C and D show the relation between the two ratings and the price of perfumes. Perfumes that are of low price have a generally smaller number of reviews (the bell of a violin plot is concentrated close to 0) as opposed to more expensive perfumes, say those costing more than £150/100ml or more. However, several perfumes that are cheap have a very large number of reviews. Panel D shows that the intervals of cheaper perfumes (price smaller that £100/100ml) seem to be composed of a larger variety of perfumes: some with high score and some with low, whereas the more expensive perfumes have consistently high scores. Despite some differences in the spreads and distributions of W and V for perfumes in different age and price brackets, the figures do not reveal any strong correlation between the age or price of a perfume and its success.

https://doi.org/10.1371/journal.pone.0218664.g004

We start by looking at the most successful perfumes to see if there are any common features. We began by studying the top-50 (roughly 5%) of perfumes, based on number of reviews V p and by weighted score W p . After all, the price of a perfume covers many different costs, not just the ingredients. “3% of a perfume price is a smell” [ 28 ], the rest is packaging, advertising and margins. However, when we look at the top fifty lists, they contain perfumes which are very different.

One important factor in the success of a perfume can be its branding. As pointed out in [ 28 ], there is a handful of companies, that constitute a majority of fragrance industry. As expected, both lists of successful perfumes are dominated by well-known brands, such as Dior , D&G , Chanel , Nina Ricci . These brands may be more successful in the perfume industry because they have large revenues and monetary privilege enables such firms to create the best marketing campaigns.

The weighted rating W p highlights some cult perfumes, such as “N°5” by Chanel, Dior’s “Poison”, and “Champs Elysees” by Guerlain.

We also see classic vintage perfumes, some of which are no longer produced such as “Tabac Blond” by Caron (released in 1922). Celebrity perfumes also feature in the highly rated perfume lists, such as “White Diamonds” under the Elizabeth Taylor brand (produced by Elizabeth Arden). This is in agreement with a hypothesis that branding influences success of a perfume, as the name of a celebrity is a branding tool in and of itself.

Affordability can play a role as mid-range or even budget brands, such as L‘Occitane and Avon, are also present in the lists of very popular perfumes. Their products being cheaper may well consist of lower quality ingredients.

What these lists of the top fifty most successful perfumes show is that none of the elements highlighted here, brand size, cult status, vintage classics, celebrity endorsement or price, seems to be the single determining factor in the success of these perfumes. This motivates us to look at the ingredients, using network methods, to see if these can throw light on what makes a successful perfume. Before that, we can look at the whole data set, not just the top fifty perfumes, to see if the age of a perfume or its price has an obvious effect on success.

We have both the age of a perfume (time since the launch date) and, in many cases, the price. We have looked to see if there was any simple relationship between the age, price and the popularity of perfumes. To do this the data was binned, with wider bins for very old or very expensive perfumes where the data is sparse.

Our database consists of 7635 perfumes with information about launch date. As seen in Fig 5 , the majority of perfumes in our dataset were launched relatively recently, around 95% were launched in the last twenty years. In fact over the last sixty years, the number of perfumes with at least one rating in our data falls off roughly exponentially with age, ∼ exp( y /9.9) where y is the number of years since the perfume was launched, roughly 10% less each year we go back.

Note the first two point cover more than a decade but all the others are decades. Note the roughly exponential rise from the 1950’s. On the right, the number of perfumes launched in various price brackets. The density of perfumes per bin is shown and these are plotted at the mid-point of the bin. Again the distribution falls off roughly exponentially.

https://doi.org/10.1371/journal.pone.0218664.g005

There is also a small peak in the number of perfumes in our data which were first created in the 1920’s and 30’s. This is when the first perfumes using artificial molecules were introduced creating the opportunity for both new sensations and for cheaper scents. The first perfumes to exploit this had a unique opportunity to create a fragrance with a large following that would then be some protection against similar examples created later. This may explain why it is noticeable that perfumes created in this era are still discussed and even available today. The classic example here is “N°5” by Chanel which was the first perfume to use the synthetic compound ‘floral aldehyde’, developed in 1921 by the famous perfumer Ernest Beaux.

Fig 5 also shows that the number of perfumes also falls away very sharply with price as we would expect. Very roughly the number per price unit fell as ∼ exp( v /70) where v is the price in units of £ per 100ml.

The interesting question is to see whether there is any relationship between the age or price of a perfume and its success. Our findings are visualised in Fig 4 (further tables are given in the Supplementary Information).

Panels A and B of Fig 4 show that there is little relation between perfume age and popularity, captured by either the number of reviews V p or the weighted score W p .

The weighted rating varies more for the recent perfumes, where the older ones (created in the first quarter of 20th century and earlier) have more stable relatively high scores of around 4. This means that both the number of reviews and the average score of those ratings ought to be high for the old perfumes. Perhaps the old perfumes withstood the test of time and are more likely to be universally acclaimed as high-quality perfumes, while the newer ones are much more varied in quality.

Panels C and D of Fig 4 show the relation between the price of the perfumes and their acquired popularity scores. Evidently, high quality and natural odourants are expensive, putting a high price tag on the resulting products. However, there seems to be little relation between the price of perfumes and their weighted ratings or the number of reviews received. One explanation is that most people automatically take ‘value for money’ into account in their rating, that is they normalise their rating to take account of the fact that they expect more from an expensive perfume. Another issue may be that different groups of people are rating cheap and expensive perfumes. Such hypotheses would require a richer dataset than we have here, one which provided information on each reviewer (e.g. socioeconomic background) and the individual perfume ratings they have made.

So none of the factors discussed so far appear to be the sole key to the success for a perfume. Turin [ 28 ] when discussing the price of a perfume suggests that “…in fine fragrance there is a threshold below which a good fragrance is impossible, and we are probably there right now. However, more dosh does not necessarily mean better perfumes: some of the great fragrances of the past were relatively cheap formulae, and it is still quite possible to mix expensive raw materials and get an expensive mess”. So it appears that the choice of ingredients and the way they are combined is vital for the success of a perfume so we now turn to study the notes used in perfumes.

Network results

We also used a permutation test with 10,000 permutations to look for significant effects of a popular note [ 30 , 31 ]. We use this to associate our d -score with a p -value which is the fraction of the random permutations which gave a larger d -score than found with the data. So a d -score with small p -value indicates that the effect seen in the data is significant as it is different from what would be found in the random case. We saw little difference in the result when using a larger number of permutations and thus concluded that 10,000 trials suffices.

We only considered notes that featured in at least 100 perfumes with ratings where we might expect to have enough information to produce statistically significant result. The results for the ten most popular notes are summarised in Table 1 . For these very popular notes, the perfumes containing these notes have a larger customer interest, d > 0, but the effect is “small”, d ≪ 1. The p -values obtained from the permutation tests validate the significance of these results for all but two notes: Bergamot and Mandarin Orange , for which p -value is relatively large (larger than 0.01 which is a common confidence threshold).

We say that the note is of specific type if most of perfumes list it as a note of this type (some notes are “mobile” in this sense: a note listed as, e.g. a heart note in one perfume may be listed as a top note in another). Note that this classification does not create hierarchy in notes: for instance, it is not clear whether the base note is hierarchically superior to top note. The last three columns contain information about how influential the note is for the number of reviews perfumes receive. The size of this effect on perfume ratings is calculated using d of ( 2 ) (we used the standard notation to describe the effect size). To evaluate the validity of the result, we used the p -value of the permutation test. As the p -values show, we can confidently state their effect sizes except for Bergamot and Mandarin Orange . The effect sizes for the most popular notes are “small” at most. In our dataset, “medium” was the largest effect size of individual notes that was encountered. None of the top-10 most popular notes have such a large effect size.

https://doi.org/10.1371/journal.pone.0218664.t001

On the other hand, we did find 60 notes with p ≤ 0.01 associated with their d -score. In Table 2 we show the notes with the largest effect sizes showing clearly that these are not the ones used the most frequently (the most popular). From this we see that only five notes have more than a ‘small’ effect on perfume ratings: Anise , Orris Root , Orchid , Bamboo and Carnation .

The note types are: H—heart, B—Base, or T—Top. We only considered notes that were present in at least 100 perfumes (around 1% of perfumes) and had p -value of the resulting d-score of no more than 0.01. We give Cohen’s d score and the descriptor in each case, along with a p -value assessing the significance of the description, so p < 0.01 suggests the description is reliable. We see that only five notes of our 990 have at least a moderate impact on perfume ratings: Anise , Orris Root , Orchid , Bamboo and Carnation .

https://doi.org/10.1371/journal.pone.0218664.t002

So far we have looked at the effect of a single note on a perfume. However, perfumes contain combinations of notes, accords, which are carefully chosen. To illustrate, the example in Fig 1 shows an accord of Jasmine and Sicilian Lemon occurred twice, as this combination of notes features in two perfumes. An accord of Vetiver and Honeysuckle occurred once in Chanel’s “Cristalle”, whereas an accord of Musk and Vanilla was not observed. If these two perfumes are successful, it might indicate that the Jasmine / Sicilian Lemon accord is an important aspect of that success. Searching for accords is analogous to a search of network motifs [ 32 ] in the perfume-note graph.

We counted the frequencies of accords (how often they occurred in the dataset) of two and three notes and compared them to the corresponding frequency in our null model. It allowed us to find both the over- and under-represented accords. We set the following criteria when looking for accords whose over- or under-representing in the data was significant: the observed accord must occur in at least 1% of perfumes, either z > D + = 2 or z < D − = 0, and the p -value is less than 0.01.

Using our criteria, we found 424 significant accords of size 2 with z ≥ 2 and 764 significant accords with z ≥ 2 of size 3. The results of our findings are summarised in Table 3 .

These accords also satisfy the criteria to appear in at least 1% of perfumes and the p -value associated with the z -score is less than 0.01. The first five accords (in italics) are those which are the most over- and under-represented in the data (largest | z | values). The remaining rows have the significant accords z > 2 with the largest effect size ( d -score) on the number of reviews of perfumes, at least 0.6 for accords of size two or 0.8 for accords of size 3. Such a large effect size means that perfumes which include these accords have a significantly larger number of reviews than you would expect.

https://doi.org/10.1371/journal.pone.0218664.t003

There is no clear relationship between z -score and d -score, as shown in Fig 6 . That suggests that simply using the most over-represented accords does not guarantee a successful perfume. There is, however, a significant number of outliers, with either extreme z -values or with large d -scores.

The two variables seem to be at best weakly related. The colour of a point indicates the p -value of the permutation test as shown in panel on the right of each plot.

https://doi.org/10.1371/journal.pone.0218664.g006

The most over-represented accords ( z ≫ 2, see Table 3 ) seem to be composed of notes that are also very popular (see Table 1 ), such as Musk , Jasmine , Amber and Sandalwood . There does not seem to be a common trend—these most over-represented accords are not composed of polar opposite notes nor of very similar notes. Also we did not see any particular tendency to combine notes of similar nor different types ( top , heart or base ). The conclusion, therefore, is that these over-represented note combinations are indeed discovered by experimentation and multiple testing conducted by the ‘Nose’.

For instance, successful accords are not always made of notes of the same type. Two notes of different volatilities (different molecule sizes) may smell very similarly (share more of the odour compounds), and thus be more similar than some pairs of notes of the same type. Testing this idea further would require a richer dataset. At the same time, it can also be a good idea to combine notes with different smells. This happens in food as different cuisines can show a preference for similar tasting ingredients or they may combine ingredients that taste very different [ 17 ]. The musical analogy made for perfumes is again relevant as the notes combined can sound harmonious or dissonant and both can contribute to a successful piece.

However these accords which are most over-represented, those with large z -score such as shown at the top of Table 3 , are not those with the largest effect on the number-of reviews (large d -score). This is also clear from Fig 6 .

Table 3 shows the accords that have the most influence on the number of reviews. The most influential accords are: Oakmoss , Lemon and Amber ; Oakmoss , Jasmine and Lemon ; Sandalwood , Lemon and Oakmoss ; Amber , Oakmoss and Jasmine ; Jasmine , Violet and Cedar . Some examples of perfumes that consist of such accords are: “Eau Sauvage” by Christian Dior, “N°5” by Chanel; “Acqua di Gio” by Giorgio Armani; “White Diamonds” by Elizabeth Taylor; “J’adore Dior” by Christian Dior, “CK One” by Calvin Klein. Thus our approach highlights perfumes that have high number of reviews V p as well as a weighted score W p by exploring the accord compositions that have strong effect size for the success of the perfumes.

We also looked at under-represented accords, finding 39 significant accords of size equal to two and one significant accord of size equal to three that have z -scores smaller than or equal to minus one and p-value larger or equal to 0.99, see Table 1 . We were able to distinguish some interesting structure for such under-represented accords as we noted some are composed of notes similar in nature, such as Woody Notes and Sandalwood , Bergamot and Citruses , Lavender and Jasmine . For instance, Sandalwood is a wood thus the two notes are wood-related scents; Bergamot has a citrus smell, so is similar to citruses. One explanation could be that in a perfume we sometimes look for an interesting combination of a variety of diverse notes, rather than combine many similar notes so there is no point in using accords of very similar notes. There are a few interesting examples, for instance, Musk , Vetiver and Vanilla seem to have a large effect size of d = 0.63, yet is under-represented. Thus, perhaps some of the accords with negative z -scores indeed are potentially unexplored great combinations.

The resulting enhancement graph network has 165 nodes with 530 edges, whose total weight is 1423—the number of enhancing events. The largest weakly connected component contains 163 nodes and 529 edges (weight is 1422). The largest centrality notes and their centrality scores are summarised in Table 4 . We saw little difference in results for different PageRank parameter α (see Supplementary Information) values between 0.7 and 0.95 so we show results for the traditional value of 0.85.

https://doi.org/10.1371/journal.pone.0218664.t004

Notes, with the highest enhancement effect fall into two categories. First, the high degree notes ( musk , vanilla , jasmine ) generally tend to enhance the composition. This is quite expected, as perhaps due to their universality they are popular notes to use in perfumery. Secondly, the list is dominated by generic notes, such as woody notes or green notes . Perhaps these are the ingredients that are not publicly disclosed, some “secret formulas” that make perfumes more complex and give depth to compositions.

There are a few under-represented accords, which could just be poor combinations. However, two of them, Jasmine / Mint and Musk / Vetiver / Vanilla do have a large positive effect on perfume ratings. Our results suggests these accords should be more popular than they currently are and that they deserve more attention in the future.

To understand whether there is a correlation between popularity of accords and perfume success, we estimated the effect size on the number of reviews for accords of size two and three as well as individual notes. We found that the combinations with the strongest effect sizes are not the most over-represented. The largest effect sizes are that of accords of Oakmoss and Lemon with either Amber or Jasmine . So by using customer review and basic recipes for perfumes in terms of notes, our methods are able to retrieve the perfumes with high customer popularity scores, highlighting the accords which the experts have found to work well.

There are other well-known methods for studying collections of items in data, such as using k − itemset analysis to produce association rules used to recommend additional items for customers to buy: notes are items, accords are itemsets, and perfumes are ‘customers’. In the simplest cases such analyses rely on the frequency of accord/itemsets but do not distinguish between different customers/perfumes. We found that in itself did not help in our analysis and in our approach we emphasise that our perfumes are very different, as denoted by the votes given to each one.

Our work provides insights into factors that play role in the success of perfumes. It also sets up a framework for a statistical analysis of fragrances based on simple properties and customer reviews. It could be a beneficial tool for systematic ingredient selection and act as an artificial Nose .

Supporting information

S1 appendices..

https://doi.org/10.1371/journal.pone.0218664.s001

Acknowledgments

V.V. acknowledges support from EPSRC, grant number EP-R512540-1.

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Evaluation of pollutants in perfumes, colognes and health effects on the consumer: a systematic review

Zahra kazemi.

1 Research Center of Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran

2 Department of Environmental Health Engineering, School of Public Health, Iran University of Medical Sciences, Tehran, Iran

Ehsan Aboutaleb

3 Department of Pharmaceutics, School of Pharmacy, Guilan University of Medical Sciences, Rasht, Iran

Abbas Shahsavani

4 Environmental and Occupational Hazards Control Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran

Majid Kermani

Zohre kazemi.

Cosmetic products, especially perfumes and colognes, are widely used in various communities. However, the use of these products can have side effects on consumers. This article aims to review the relevant literature published up to August 2020 to determine whether perfumes and colognes can affect people’s health. Relevant articles were identified through electronic search. A total of 562 articles were selected and finally 37 related articles were included in the study after the screening process. The results of this systematic study showed that phthalates, aldehydes, parabens and aluminum-based salts are the most important contaminants in aromatic products that cause side effects such as allergies, breast cancer, reproductive disorders, especially in males, skin allergies, nervous system damage and migraine headaches for consumers. The incidence of complications in people using these products depends on parameters such as age, gender, race, amount of substance consumed, duration of use and economic status, and regarding the relationship between diseases such as cancer, respiratory disorders and endocrine with common contaminants in aromatic products, incidence of these diseases is probable in consumers which require further research to prove.

Introduction

Smells play a significant role in human behavior. A pleasant scent can have a calming effect, but an unpleasant odor can lead to anxiety and discomfort. The first evidence of perfume use by human dates back to thousands of years ago, when Egyptians used herbs, gums, and resins as aromatic compounds in their religious rites [ 1 ]. Today, perfumes are used in various applications, including deodorants, laundry products, shampoos and conditioners, cleansers, etc. These compounds include two groups, natural and synthetic. Natural perfumes are divided into two categories: aromatic compounds and musk, which are extracted from plants, lichens, seaweed and special oil obtained from different parts of a plant. The other group is synthetic aromatic compounds, which are often used as alternative sources due to low production costs and problems related to low product quality or lack of resources [ 2 ]. Aromatic products contain a complex mixture of chemicals such as volatile organic compounds (VOCs), limonene, alpha-pinene, beta-pinene, ethanol, acetone, acetaldehyde, etc. [ 3 ]. Phthalates such as diethyl phthalate (DEP), dibutyl phthalate (DBP), dimethyl phthalate (DMP), and diisobutyl phthalate (DiBP) in deodorants, shampoos, soaps, cosmetics, nail polishes and parabens, among others. Methyl paraben (MP), butyl paraben (BP), ethyl paraben (EP), and propyl paraben (PP) are used as fungicides, bactericides, and preservatives in cosmetics, perfumes and deodorants [ 4 , 5 ]. Diethyl phthalate is a chemical used to make perfumes last longer. The U.S. Clean Water Act lists it as a toxic and priority pollutant [ 5 ]. Dimethyl phthalate and diethyl phthalate lead to slower evaporation of perfume aromas which results in longer persistence [ 6 ]. Scientific evidence shows that four phthalates in 102 hair sprays, perfumes, fragrances and nail polishes, DBP in 19 of 21 nail polishes and 11 of 42 perfumes, as well as DEP in 24 of 42 perfumes and 2 of 8 aromatic substances were observed [ 7 ]. Triclosan is an antimicrobial substance that was widely used in antibacterial hand soaps and was banned by the FDA in 2016, but is still used today in some compounds such as fragrances, toothpaste, mouthwash and acne cream [ 5 ]. Complications of using perfume include neuropathy (depression, autism), neoplasms (breast cancer, prostate cancer), effects on the liver, migraine headaches, asthma attacks, mucosal symptoms (watery or red eyes, sneezing), neurological problems (dizziness, convulsions, headache, fainting, imbalance), respiratory (cough, shortness of breath), skin (skin rash, urticaria, redness of the skin, skin tingling, dermatitis), immune system (swollen lymph nodes, fever, fatigue), gastrointestinal tract (nausea, bloating, diarrhea) and cardiovascular (rapid or irregular heartbeat, tremors, chest discomfort) [ 3 , 8 ]. About 75% of people with shortness of breath have experienced asthma attacks caused by perfumes [ 8 ]. Also, risk of asthma and high IgE serum levels were increased in the children who were exposed to phthalates during pregnancy. [ 9 ]. Furthermore, there are some concerns about the effect of diethyl phthalate on male fertility; so this group should avoid using perfume products that contain large amounts of diethyl phthalate [ 10 ]. Triclosan and some parabens have significant effect on the spread of cancer and triclosan can disrupt thyroid function [ 5 ]. The findings of a survey in the United States, Australia and the United Kingdom indicated that on average, in all three countries, about 30% of people were exposed to at least one fragrance [ 3 ]. Among many factors, aromatic compounds with estrogenic properties (parabens, phthalates, nitro musks) have been an important and main cause of breast cancer. These compounds penetrate the bloodstream through the skin and lead to impaired endocrine homeostasis [ 8 ]. Studies on children in the age range of 5–15 showed that the most common allergens in the development of dermatitis are paraben (43%), potassium dichromate (27%) and perfume (26%) [ 11 ]. Many studies show that most perfumes, even in small amounts, can cause neurological disorders in the fetus of pregnant mothers [ 8 ]. One of the causes of autism is exposure to chemicals (perfumes and medications) during pregnancy and after birth through breast milk [ 8 ]. Studies show that aromatic products emit more than 100 volatile organic compounds (VOCs), which can pose a serious threat to human health. The purpose of this study is a comprehensive review of different types of contaminants identified in these products and the adverse effects observed in people exposed to them. Attempts were also made to identify and categorize the incidence of complications in these individuals and the factors affecting the incidence and severity of complications.

Material and methods

Literature review.

The search was done in three databases: Scopus, Pabmed, and Web of Science in 2020 for finding relevant articles regarding th perfume pollutants and their effects. As shown in Table  1 , a total of 672 articles were found, of which duplicates were removed.

Search protocol and the number of articles found in each database

Eligibility criteria

The final papers were chosen on the basis of the eligibility criteria; for this purpose, the focus was on articles which were related to the pollutants in perfumes: 1) Articles which studied the presence of pollutants, 2) measured the concentration of pollutants, and 3) articles which evaluated the effects of pollutants on consumers or people exposed to perfumes.

Study selection

The literature was screened independently by all the authors, based on the criteria mentioned above.

Three screening steps were performed to select the final articles. In the first step, according to the title of the article, articles related to perfumes were selected (83 articles). In the second step, articles focusing on perfume’s pollutants were selected after reviewing their abstracts (52 articles). Finally, (37) articles which carried information about the quantity or effects of pollutants in perfume were selected for writing this review (Fig.  1 ).

Outlines of the screening process and selected 37 articles used in this study

Data extraction

We extracted the following data on the content of the eligible articles:(1) Pollutants in perfumes and colognes, (2) Concentrations of pollutants in perfumes and colognes (3) Diseases attributed to aromatic products consumption (4) Factors affecting the incidence of effects (5) Methods of prevention or treatment.

Results and discussion

Pollutants (harmful compounds) in perfumes.

Aromatic consuming products contain a complex mixture of chemicals that have different uses including odor production, solvent and fluidizer, perfume stabilizer, preservative, antiperspirant, denaturing agent [ 12 – 17 ]. Numerous studies have been conducted on the compounds in these products and the results are presented in Table  2 . Although the use of these compounds in aromatic products has been mentioned for a number of reasons, many of them have negative effects on health and are known to be contaminant. Examples of volatile organic compounds (VOCs) of ethanol, alpha pinene, acetone, limonene, beta pinene and acetaldehyde are mentioned in aromatic products as indoor air pollutants [ 3 ]. The number of compounds in aromatic products reaches tens of compounds, many of which have toxic effects on humans; (2015) Steinemann in his study identified more than 150 different VOCs distributed from 37 aromatic consumer products in the United States, 42 of which were classified as toxic or hazardous pollutants under U.S. federal law [ 3 ]. It is possible to identify the harmful effects of exposure to these compounds on human health; in a way that the concentration of monoester phthalate in cologne in a urine sample was measured by liquid chromatography with mass spectrometry [ 7 ]. Also in another study, five phthalate monosters was observed in 75–100% of people; it was found that MEP was the most common (100%), followed by MBP (95%) and MBzP (90%), while MEHP and MMP were observed for 75% of people [ 7 ]. In addition, some compounds in fragrance products can cause secondary contaminants. Due to the high content of terpenoids in air fresheners, large amounts of secondary pollutants such as formaldehyde and fine particles may be created as a result of their release [ 18 ]. It has also been reported that terpenes (e.g. beta-pinene, limonene and alpha-pinene) as important contaminants in aromatic products can react with ozone and spectrum and from a wide range of secondary contaminants such as formaldehyde, acetaldehyde and secondary organic aerosols [ 13 , 19 , 20 ]. Therefore, the release of pollutants from the consumption of aromatic substances, in addition to the consumer, can affect the health of other people directly or by producing secondary pollutants in indoor air. For example, the results of an indoor air survey of kindergartens and apartments show that DEHP, and to some extent measured DBP in kindergarten air, was significantly higher than in apartments, and that DEHP accounted for approximately 80% of the most important pollutants in house dust [ 21 ]. The highest share of air pollutants was in DBP with a ratio of approximately 32%, followed by DEP with diethyl phthalate in a ratio of approximately 19%, while DEHP had a higher share (5–12%) in kindergarten air [ 21 ].

Compounds identified in perfumes and their applications

Adverse effects of using perfume and cologne

The compounds identified in aromatic products can be the source of several adverse health effects. One of the side effects of using these products that has been mentioned in most research results is allergies. Sensitivity to the potential for allergenicity is when the compounds penetrate the skin and trigger an immune response [ 35 ]. For example, the results of the Marie Api study suggested that 3.5% of the population were allergic to aromatic compounds [ 14 ]. Terpenoids and other herbal fragrances have also been shown to cause skin allergies [ 18 ]. On the other hand, inhaling DEHP aerosols in combination with allergens can lead to asthma and allergies in children [ 6 ]. Dermal or inhalation exposure has been shown to lead to skin and bronchial sensitization [ 8 ]. However, according to the research results, allergies and allergic symptoms do not appear in all people exposed to aromatic products, and the proportion of people with these side effects in the study population has been reported differently. According to a study on 90 student nurses,12 cases (13%) showed fragrance allergic[ 2 ]. In a survey of 567 unselected individuals aged 15–69 years, 6 cases (1.1%) reacted to fragrance mix [ 36 ]. Also, when allergies were tested with ten popular perfumes, it was found that complications appeared in 6.9% of women with female eczema patients. In a study, sensitivity to popular commercial fragrances was reported in 57% of patients [ 36 ]. In addition, the degree of allergic symptoms incidence in people will have different consequences depending on which aromatic product is used, in a way that the most common allergen reported in 50 patients with suspected CACD in 2000 in India was perfume (47%) [ 37 ]. Perfumes were also identified as the most common allergens when patients with suspected allergic cosmetic dermatitis were examined [ 36 ]. Research has shown that perfumes can also cause allergic reactions in pets. In a study in European centers on 5% of pets, the rate of 1.5–3% of contact allergies caused by perfume was observed [ 33 ]. Of course, it should be noted that different compounds in aromatic products can cause allergic symptoms in humans, which are mentioned in Table ​ Table2. 2 . However, the presence of several allergenic factors has led to some studies to mention perfumes as one of the main allergens [ 37 , 38 ]. Also, in a study conducted in skin clinics on patients with allergic dermatitis, “perfume” was considered as the second main cause of allergic reaction [ 5 ].

In addition to allergies, the use of perfumes and colognes, as shown in Fig.  2 , have other adverse effects on the health of consumers, the most important of which are respiratory problems and diseases such as asthma [ 1 , 5 , 8 , 24 , 39 ]. A Swedish study reported respiratory problems (20.0%) and asthma attacks (5.5%) in the population exposed to perfumes and colognes [ 3 ]. In other studies, respiratory problems were observed in 9.1, 11.6 and 18.6% of people exposed to perfumes and colognes [ 19 , 20 , 40 ]. It is confirmed that respiratory problems in addition to perfume and cologne can be due to the use of other similar products such as body spray products [ 18 ].

Effects of exposure to perfumes and colognes

The use of aromatic products can lead to other side effects such as migraine headaches, which have been reported in some studies with proportions of 4.2, 16.1, 8.4, 15.7 in people exposed to perfumes and colognes [ 3 , 19 , 20 , 40 ]. Although the use of aromatic products has proven side effects for exposed individuals, the proportion of people with these symptoms or side effects is between 20 and 35% of all people exposed to aromatic and health products [ 3 , 19 , 20 , 40 ]. Also, other observed effects of perfume and cologne are stated in Table  3 .

Observed effects of perfume and cologne

Factors affecting the side effects of using perfume and cologne

Although the presence of perfume and cologne compounds and their adverse health effects have been proven in exposed individuals, a high proportion of people who use these products are unaware of their health effects. For example, it was reported that 70.9% of perfume and cologne consumers were unaware that fragrance products, even those called green and organic, could emit potentially dangerous pollutants [ 3 ]. This issue can be effective in increasing the incidence of side effects of using aromatic products in the whole society. In addition, other factors are effective in causing adverse effects of aromatic products. Gender is an important factor in the effects of the use of aromatic products. Research shows that women are more likely than men to suffer from the effects of using fragrance products. One study found that of 33.1% of the population, who reported adverse health effects, 64.0% were female and 36.0% were male [ 3 ]. Similar conditions have been reported for a higher proportion of complications observed in women than men with a difference of about 10% in other studies [ 20 , 40 ]. In addition to gender, age also affects the symptoms and side effects of using aromatic products. This effect can be due to the different uses of aromatic products by age groups or due to the sensitivity of some age groups to the pollutants in them. For example, parabens have been shown to have more severe effects in young children than in adults because protective mechanisms such as a competent immune system are not yet developed in children, and exposure to chemicals in the early stages of development can disrupt normal patterns of growth [ 57 ]. However, another study showed an increase in perfume allergy with aging [ 36 ]. One of the reasons for the difference in side effects between the sex and age groups is the difference in the sensitivity in these groups, as evidenced by the higher use of health products in certain age groups and women, in a way that fragrance products is an important cause of complications in teenage girls [ 58 ]. Studies have also shown that the differences in the side effects of fragrance products are the result of physical differences, income levels and well-being of individuals [ 7 , 17 ]. Environmental conditions such as temperature, humidity and chemical properties of the product will affect the incidence of adverse effects due to the effect on skin absorption [ 29 ]. Another factor influencing the occurrence of complications is the type and area of use, so that the use of axillary health products especially on the left side of the body, because of the right-handedness of most people, is associated with higher incidence of left breast cancer [ 29 ]. Important factors which show the negative effects found in other studies are collected in Table  4 .

Factors affecting the incidence of effects

Solutions to prevent complications and odor control

Given the significant effects of these products, it is very important to mention solutions to reduce its problems. One of these solutions is to increase consumer awareness about their adverse health effects through education [ 5 ]. Since aromatic products play an important role in causing breast cancer, changing the formulation of the product or deciding to discontinue consumption are other measures that can be effective [ 55 ]. Huang and his colleagues believed that in order to minimize the possibility of damage to the reproductive system, sellers of perfumes, sprays, colognes, etc., especially pregnant women, should work in areas that are not exposed to phthalates [ 42 ]. Other applications are as follows:

Development of national laws on the non-sale of cosmetics containing harmful ingredients [ 60 ].

Proper washing of the area with soap and water.

Using 20% ACH in SAGB to remove underarm odor.

Using indomethacin, diltiazem, cardism, clonidine, propranolol to eliminate odor [ 61 ].

Contaminants in perfumes and colognes and their health effects on the consumer were systematically reviewed. It was found that the most attention of researchers was to identify the compounds in perfumes and colognes and their concentrations. Among the most common pollutants phthalates and their derivatives can be mentioned. Other pollutants included parabens, triclosan, salicylates, terpenes, aldehydes, benzene, toluene, styrene, and aluminum-based salts. These pollutants have also been shown to have adverse effects on consumer health such as asthma and allergies, cardiovascular disease, central nervous system damage, breast cancer, endocrine cancer, respiratory disorders, reproduction, thyroid, adrenal gland function and immune system. Factors affecting the occurrence of effects in people exposed to these products include age, sex, amount and place of use, physical differences and income levels. It was also found that not all people exposed to these products reported identified side effects. Therefore, increasing consumer awareness about the negative effects of perfumes and colognes, and trying to produce products with fewer side effects through the use of low-risk raw materials can be beneficial for protecting consumer’s health.

Acknowledgments

The authors gratefully acknowledge the financial support given by the Research Center for Environmental Health Technology, Iran University of Medical Sciences, Tehran, Iran (Grant Number:.99-3-61-19198).

Abbrevations

Declarations.

IR.IUMS.REC.1399.1379.

The authors of this article declare that they have no conflict of interests.

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Contributor Information

Majid Kermani, Email: [email protected] , Email: moc.oohay@inamrekdijam .

Zohre Kazemi, Email: [email protected] .

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Characterization of solid perfume based on Cocoa Butter with Jasmine Oil as fragrance

Melati Septiyanti 1 , Yenny Meliana 1 , Novia Suryani 2 and Hendrawati 2

Published under licence by IOP Publishing Ltd IOP Conference Series: Materials Science and Engineering , Volume 1011 , The 6th International Symposium on Applied Chemistry (ISAC) 2020 18-20 November 2020, Tangerang, Indonesia Citation Melati Septiyanti et al 2021 IOP Conf. Ser.: Mater. Sci. Eng. 1011 012037 DOI 10.1088/1757-899X/1011/1/012037

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1 Indonesian Institute of Sciences, Research Center for Chemistry, Serpong –Tangerang Selatan 15314, Indonesia

2 Chemistry Department, Faculty of Science and Technology, Universitas Islam Negeri Syarif Hidayatullah, Jakarta, Indonesia

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Cocoa butter can be obtained from by-product of chocolate powder processing from the result of mechanical pressing using hydraulic press. As a source of vitamin E, cocoa butter in cosmetic has some advantages which are to soften and moisturize the skin. Meanwhile, jasmine can be used as a fragrance in perfume and cosmetics. In this study, cocoa butter was used as raw material for solid perfume. Its optimal concentration in the product was determined. Solid perfume was made by melting cocoa butter and beeswax at 90°C followed by adding jasmine oil as fragrance. The formulation variation of solid perfume was done with cocoa butter concentration 10%, 20%, 30%, 40% and 50% (w/w) and addition of patchouli oil as fragrance fixative agent. The following tests were carried out on the products: functional group analysis, hardness test, homogeneity test, physical stability test, melting point test, antioxidant test, and organoleptic test. The result showed that the variation of cocoa butter concentration affected the physical characteristics of the solid perfume. The optimum product of solid perfume based on panelists' organoleptic test was achieved with cocoa butter concentration of 30%. It had an organoleptic score of 3.63, antioxidant activity with IC 50 value of 201.98µg/mL, hardness penetration 14.16 mm/second, melting point 90°C and pH value 4.

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Calamansi Fruit Extract as Chemical Substitute in Perfume

• Cloud Benedict Zamudio

INTRODUCTION

This study wants to test the calamansi extract as a substitute for expensive perfumes. This is because calamansi is abundant here in the Philippines. The process of making the calamansi perfume is easier and cheaper compared to making those expensive ones.

The researcher used an experimental method to know if calamansi fruit extract can be a chemical substitute in making perfumes. The experiment underwent many processes to be able to come up with results and conclusions to support the research.

Answering the first problem on the amount of the calamansi extract most effective in making perfume, (1) 7.5 mg/mL gave the perfume some fragrance but did not satisfy the whole product, (2) 12.5 mg/mL was the best amount of calamansi extract dissolved with vodka and essential oil. It gave enough fragrance but did not smell too foul; and (3) 20 mg/mL amount of calamansi extract gave a foul smell and did not satisfy the respondents.

DISCUSSIONS

Calamansi extract is a good substitute for chemicals in creating commercialized perfumes sold in the market. It promotes the usageof natural ingredients in maintaining and improving personal hygiene of a person.

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