Axillary body odor is individually specific and potentially a rich source of information about its producer. Odor individuality partly results from genetic individuality, but the influence of ecological factors such as eating habits are another main source of odor variability. However, we know very little about how particular dietary components shape our body odor. Here we tested the effect of red meat consumption on body odor attractiveness. We used a balanced within-subject experimental design. Seventeen male odor donors were on "meat" or "nonmeat" diet for 2 weeks wearing axillary pads to collect body odor during the final 24 h of the diet. Fresh odor samples were assessed for their pleasantness, attractiveness, masculinity, and intensity by 30 women not using hormonal contraceptives. We repeated the same procedure a month later with the same odor donors, each on the opposite diet than before. Results of repeated measures analysis of variance showed that the odor of donors when on the nonmeat diet was judged as significantly more attractive, more pleasant, and less intense. This suggests that red meat consumption has a negative impact on perceived body odor hedonicity.

Correlation coefficients between rated variables in first (1) and second sessions (2)

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The Effect of Meat Consumption on Body Odor Attractiveness

Jan Havlicek

1

and Pavlina Lenochova

2

1

Department of Anthropology, Faculty of Humanities and

2

Department of Anthropology and

Human Genetics, Faculty of Science, Charles University, Prague, Czech Republic

Correspondence to be sent to: Jan Havlicek, Department of Anthropology, Faculty of Humanities, Charles University, Husnikova 2075,

158 00 Prague 13, Czech Republic. e-mail: jan.havlicek@fhs.cuni.cz

Abstract

Axillary body odor is individually specific and potentially a rich source of information about its producer. Odor individuality partly

results from genetic individuality, but the influence of ecological factors such as eating habits are another main source of odor

variability. However, we know very little about how particular dietary components shape our body odor. Here we tested the effect

of red meat consumption on body odor attractiveness. We used a balanced within-subject experimental design. Seventeen male

odor donors were on ''meat'' or ''nonmeat'' diet for 2 weeks wearing axillary pads to collect body odor during the final 24 h of the

diet. Fresh odor samples were assessed for their pleasantness, attractiveness, masculinity, and intensity by 30 women not using

hormonal contraceptives. We repeated the same procedure a month later with the same odor donors, each on the opposite diet

than before. Results of repeated measures analysis of variance showed that the odor of donors when on the nonmeat diet was

judged as significantly more attractive, more pleasant, and less intense. This suggests that red meat consumption has a negative

impact on perceived body odor hedonicity.

Key words: diet, human, meat, olfaction, scent, smell

Introduction

Human body odor is individually specific, similar to our ap-

pearance. Odor individuality is established very early in life

as was clearly shown by Porter's team and other researchers

(for review, see Winberg and Porter 1998). Newborn babies

are able to distinguish their mothers' breast and axillary odor

within several weeks after delivery (Russell 1976; Cernoch

and Porter 1985). Simultaneously, mothers can recognize

the odor of their offspring 2 days after delivery (Porter

et al. 1983). Fathers can also distinguish their own baby's

smell from the smell of a strange baby when babies are aged

3 weeks (Porter et al. 1986). Individual odor recognition is

not restricted to early parent–offspring relationships, occur-

ring also in adulthood in sibling recognition for instance

(Porter and Moore 1981). In addition, body odor plays a sig-

nificant role in mate choice (Herz and Cahill 1997; Herz and

Inzlicht 2002) and in sexual partners' recognition once the

relationship is established (Hold and Schleidt 1977). Based

on all the above-mentioned empirical findings, body odor

emitted by a specific individual was therefore labeled an

''odor signature'' (Porter et al. 1985).

The odor signature is to some extent genetically inherited.

This view is supported by 3 lines of evidence. First, odors of

parents and offspring can be correctly matched by subjects

not acquainted to odor donors (Porter et al. 1985). On the

other hand, the raters were not able to match odors of

spouses, who are not genetically related. This result also ex-

cluded the possibility that matching of parents and offspring

was due to shared home odor. Second, odors of monozygotic

twins are more difficult to distinguish than dizygotic twins

(Wallace 1977), and monozygotic twins are matched at rates

better than chance, even when they live apart (Roberts et al.

2005). Third, odor preferences are correlated with genes in

the major histocompatibility complex (MHC). Products of

MHC genes are crucial elements of the immune system, par-

ticularly in self/nonself recognition. It was found that women

rate the odor of MHC dissimilar men as most attractive

(Wedekind et al. 1995; Wedekind and Fu

¨ri 1997). Such pref-

erence may potentially result in more MHC heterozygous,

and therefore also more viable, offspring (Penn 2002).

However, not only is body odor preprogrammed by genetic

factors but also much variability is due to psychophysio-

logical and ecological influences. For instance, it has been

shown repeatedly that body odor changes across women's

menstrual cycle, peaking in attractiveness around the time

of ovulation (Thornhill et al. 2003; Kuukasja

¨rvi et al.

2004; Havlicek et al. 2006). Other studies found that mood

Chem. Senses 31: 747–752, 2006 doi:10.1093/chemse/bjl017

Advance Access publication August 4, 2006

ªThe Author 2006. Published by Oxford University Press. All rights reserved.

For permissions, please e-mail: journals.permissions@oxfordjournals.org

(e.g., fear) of a target person may influence hedonic percep-

tion of his/her axillary odor (Chen and Haviland-Jones 2000;

Ackerl et al. 2002). Eating habits also may have a crucial

impact on body odor composition. However, very little is

known about the effect of individual alimentary components

on human body odor. Some folk beliefs connect odor hedon-

icity with meat consumption. For instance, Hindu Indians

who are usually vegetarian say that people who eat meat

smell bad because of it (S Komarek, personal communica-

tion). To our knowledge, however, this effect has not yet

been tested under controlled conditions.

The aim of this study was to test the effect of red meat

consumption on axillary odor hedonicity. For this purpose,

we used a balanced within-subject design with a relatively

long period (2 weeks) of diet control. The results may im-

prove our rather poor understanding of how axillary odor

is determined and also may be of methodological importance

for dietary control in olfactory studies.

Materials and methods

Subjects

Odor donors

Seventeen male students of Charles University, Prague,

agreed to participate in the study. Their mean age was

22.5 years (minimum 19 years, maximum 31 years), body

weight 75.5 kg (minimum 63 kg, maximum 88 kg), and body

height 182 cm (minimum 171 cm; maximum 200 cm). All of

them were nonsmokers, reported no dermatological or other

diseases and did not shave their armpits. The donors were

given CZK 2000 (approximately GBP 45) as compensation

for their time and potential inconvenience caused by the

prescribed diet.

Raters

Raters were contacted by e-mail or personally by the

authors. Thirty-two female students (mean age 23.3 years,

minimum 19 years, maximum 32 years) took part in the

study. Two of them, however, did not finish both sessions

and were excluded from all analyses. None of the women

were using hormonal contraception, and all reported having

''normal'' menstrual cycle length (25–40 days). They were

also asked about the date of the onset of their last menstrual

bleeding (day 1). Women in days 9–15 of their cycle on the

testing day were judged to be in fertile phase and others to be

in nonfertile phases of the cycle. As the experiment was com-

posed of 2 rating sessions, we decided to perform the second

session 28 days after the first one to minimize the possible

effect of menstrual cycle on the raters' olfactory sensitivity

(Doty et al. 1981; Caruso et al. 2001; Navarrete-Palacios

et al. 2003). The raters were not paid for participation; how-

ever, they received a perfume tester after the first session and

a 100 g chocolate bar after the second session.

Odor sampling procedure

We used a balanced within-subject design in which odor

donors were randomly assigned to one of 2 groups (A, B).

Odor donors in group A were in the ''meat'' condition for

the first session, whereas those in group B were in the ''non-

meat'' condition. Groups were reversed for the second session.

The odor donors followed our diet protocol for 2 weeks

prior to the odor sampling. They were also asked to keep

a ''diet diary'' in which they recorded all food eaten during

the day and alcoholic beverages and level of stress, fatigue,

and general mood using a 7-point scale. The diet protocol

comprised 2 stages. In the first stage (days 1–10), the odor

donors received a list of 33 meals; they had to choose at least

one main dish out of the given list every day. The diet protocol

was built in 2 versions and composed only of meat or ''non-

meat'' dishes. The individual dishes were elaborated to differ

in meat content only (e.g., vegetable risotto/pork risotto). For

the list of meals offered, see the Appendix (Supplementary

material). Each participant received instructions and restric-

tions in a written form. They were instructed to refrain from

1) using perfumes, deodorants, antiperspirants, aftershave,

and shower gels, 2) eating meals containing garlic, onion,

chilli, pepper, vinegar, blue cheese, cabbage, radish, fer-

mented milk products, and marinated fish, 3) drinking alco-

holic beverages or using other drugs, and 4) smoking. As this

very strict procedure had to be maintained for a relatively

long period, during the first stage (days 1–10), nonserious vio-

lations were tolerated (e.g., one 0.5l beer or one glass of wine).

In the second stage (days 11–14), all food (3 meals and 2

snacks a day) were provided to odor donors in order to pre-

cisely control their dietary intake. The meat group members

were served a 100-g red meat dish for each main course (i.e.,

lunch and dinner); the nonmeat group again differed only in

the absence of meat. For particular meals served to the odor

donors, see the Appendix (Supplementary material). Odor do-

nors were reminded not to break the restrictions given in the

first stage. For the second stage, they were provided with

nonperfumed soap (Sara Lee Household & Body Care,

Stockholm, Sweden) and were asked to avoid exaggerated

physical activities, sexual activity, and sleeping in the same

bed as their partner.

To check the odor donors' conformity with the instructions,

we carefully examined the ''diet diaries.'' Two of the donors

when on nonmeat diet reported once having a meat dish dur-

ing the first stage of the diet protocol. All donors when on

meat diet reported having at least a small amount of meat

every day. Most of the subjects reported having a small

amount of alcohol beverages (e.g., 0.5l beer or one glass of

wine) on some days during the first stage of the diet protocol.

Two donors in nonmeat and 2 donors in meat condition

reported beer or wine consumption during the second stage

of their diet. No consumption of spirits was reported.

Cotton pads, a T-shirt, plaster, 2 zip-lock plastic bags for

storing the pads from left and right armpits, and an

748 J. Havlicek and P. Lenochova

instruction sheet were provided to each odor donor 2 days

before the rating session (day 15). In the evening of day 13,

the odor donors were asked to shower without using even

the nonperfumed soap. Odor donors then applied the cotton

pads in the morning (7:00 AM) of day 14 and wore them

for 24 h in total.

Cottonpads (Ebelin cosmeticpads, DM-drogerie markt,Ceske

Budejovice, Czech Republic, http://www.dm-drogeriemarkt.

cz)served as stimuli, a method used in several previous stud-

ies (e.g., Havlicek et al. 2005, 2006). The pads were 100%

cotton, elliptical in shape, approximately 9 ·7 cm at their

longest axis. In the morning, the odor donors fixed their cot-

ton pads to both armpits by using 3 M Micropore surgical

tape and wore them for 24 h. To avoid odor contamination

from odor donors' clothes or background odor, the donors

were asked to wear new white 100% cotton T-shirts (previ-

ously washed without washing powder) as the first layer of

clothes. The next morning they put the pads into the zip-lock

plastic bags and handed them back to the experimenters. As

we received samples from both armpits from each donor, we

randomly chose one of them for the testing session. To avoid

possible effects of refrigeration on the stimuli, olfactory rat-

ing of the samples started within an hour after collection.

Odor rating procedure

Ratings took place in a quiet, ventilated room. The tempera-

ture during the first session was 20.5–21.5 C (44–48%

humidity) and 20.5–21.5 C (35–37% humidity) during the

second session. Raters were asked to attend the session ap-

proximately at the same time for both sessions in order to

avoid possible temporal changes of rated odors and/or diurnal

fluctuation in olfactory abilities. Stimuli (pads) were encased

in 250 ml opaque jars labeled by a 2-number code for the first

session and by a 2-letter code for the second session. Stimuli

were split in 2 sets. Each subject rated both sets (i.e., 17 stim-

uli). The order of sets and order of stimuli within a set was

randomized in the first session. In the second session, the order

of sets was the same as in the first session for each subject.

However, the order of stimuli within a set was again random-

ized. This design ensured that each stimulus was assessed by

all raters in both conditions and in a balanced order. Stimuli

were rated on a 7-point scale for their 1) intensity, 2) pleasant-

ness, 3) sexual attractiveness, and 4) masculinity. Both ends of

each scale were anchored by verbal descriptions (e.g., very

unpleasant and very pleasant). The ratings were written down

immediately after sniffing each stimulus, but the time spent

by sniffing was not restricted. Raters had an approximately

10-min break between the 2 sets to avoid possible odor habit-

uation. Coffee, tea, mineral water, and a small snack (i.e.,

cookies) were offered to raters, and they were also asked to

complete an additional questionnaire during the break.

Statistical analysis

As our design was within subject, repeated measures analysis

of variance (ANOVA) was used. The data were analyzed in

2 different ways: 1) using mean odor donors ratings and 2)

using mean subjects (raters) ratings as the unit of analysis.

Each of the approaches has its specific advantages and dis-

advantages. The statistical package STATISTICA 7.0 was

used for all testing. To test the possible effect of repeated test-

ing, we performed repeated measures ANOVAs for each of

dependent variables (e.g., pleasantness) using odor donors as

unit of the analysis. The same procedure was performed with

subjects as unit of the analysis. We did not find a difference

between the first and the second session in any of the odor

ratings (all P> 0.4). There was also no difference between the

sessions in self-evaluated stress, fatigue, and mood of the

odor donors (all P> 0.1).

Results

First, we used individual odor donors as a unit of the analysis.

Mean ratings for each odor donor in experimental (meat) and

control (nonmeat) conditions were calculated. These means

were entered into ANOVA as repeated measures. Odors from

individuals in the nonmeat condition were rated as more

pleasant, attractive, and less intense. However, none of the

tests reached formal level of statistical significance.

The first type of the analysis is rather crude as it uses only

overall means of each donor and does not take into account

the differences in individual ratings across the experimental

conditions. Thus, for the subsequent analyses, we used indi-

vidual raters as units of analysis (Figure 1). This approach

was possible due to the fact that all raters assessed all samples

in both conditions in a balanced design. Samples in the non-

meat condition were rated more pleasant (F

1,29

=7.0; P =

0.01), more attractive (F

1,29

=7.7; P <0.01), and less intense

(F

1,29

=7.0; P =0.01) (Figure 2).

No difference was found in masculinity rating. We further

analyzed the potential influence of physiological (menstrual

cycle phase) or social conditions (coupled/single status of

raters) by including them as independent variables into the

analysis. Both the menstrual cycle phase and partnership

status were entered as binomial variables. There was neither

any effect of menstrual cycle phase or partnership status on

any of the dependent variables (e.g., attractiveness) nor any

interaction with dietary condition observed.

The relations between rated variables were analyzed by

simple correlation analysis using mean subject's value as

a unit. We found highly significant correlations between

all but one rated variable within one session. The only non-

significant correlation was between attractiveness and mas-

culinity during the second session. None of the correlations

were, however, significant between the 2 sessions. All corre-

lation coefficients are shown in Table 1.

We also analyzed self-rated levels of stress, fatigue, and

general mood, each of which may potentially influence body

odor. Each donor wrote down his mood every day when on

the prescribed diet (i.e., over 14 days). We computed mean

values for each odor donor and compared them between the

Effect of Meat Consumption on Body Odor 749

diets. Results of repeated measures ANOVA showed no dif-

ference in stress, fatigue, and mood (all P> 0.5).

Discussion

The results of this study show for the first time that red meat

consumption may have a perceivable impact on axillary

body odor. Odors of donors on the nonmeat diet were judged

as more pleasant, more attractive, and less intense. This pat-

tern was not influenced by raters' menstrual cycle phase or

partnership status.

The number of odor donors was relatively small (17 men).

However, the nature of the experiment was balanced and

within subject. In other words, each rater assessed some

donors first in meat condition and some donors first in non-

meat. Moreover, the diet we prescribed to our odor donors

was identical except the meat content (e.g., fried pork steak

with potatoes, fried Edam cheese with potatoes). This gives

us high confidence that our results are due to the studied ef-

fect (i.e., meat) and not due to some other variable (e.g., day

of the testing). Theoretically, our diet may have influenced

the mood of the donors, which may in turn have an impact

on quality of body odor (Chen and Haviland-Jones 2000;

Ackerl et al. 2002). However, this is probably not the case

as we did not find differences in self-rated stress, fatigue,

and mood between meat and nonmeat conditions. The reli-

ability of the results is also supported by the fact that mean

ratings across the 2 sessions were not significantly different

and that there was no change in masculinity rating across

the experimental conditions. The relative stability of odor

femininity–masculinity was found previously in a sample

of women donors (Havlicek et al. 2006).

Potentially, our findings may be a result of different ener-

getic (protein) values. In other words, our diet only differed

in meat content and therefore in energetic value. Thus, this

factor can be responsible for the effect, not the meat per se.

However, if this would be the case, one may expect diet of

higher energetic value (i.e., meat diet) to be more attractive as

was found in the bank vole study (Ferkin et al. 1997). Our

results show higher attractiveness in the nonmeat diet,

and we therefore believe that it is caused by the meat effect

specifically.

Figure 1 Mean difference between nonmeat and meat diet conditions in ratings of body odor pleasantness, attractiveness, and intensity for each subject

(rater). Values above zero indicate higher ratings in nonmeat condition.

Figure 2 Mean ratings (± SE) of axillary odor pleasantness, attractiveness,

and intensity when body odor donors were on meat diet (white bars) and

when on nonmeat diet (gray bars). Differences are significant at P= 0.01

(repeated measures ANOVA).

750 J. Havlicek and P. Lenochova

We found a significant positive correlation between odor

intensity and masculinity. This phenomenon is consistent

with earlier findings on gender discrimination by smell. Doty

and colleagues showed that more intense smells are usually

judged to be masculine (Doty et al. 1978, 1982). The negative

correlation between the rating of pleasantness or attractive-

ness and subjectively perceived intensity was also observed in

earlier studies (Havlicek et al. 2006). One may argue that the

higher attractiveness of donors on the nonmeat diet is due to

quantitative rather than qualitative changes in their axillary

odor. In our view, however, meat consumption changes the

composition of some axillary chemicals (see in the second

paragraph below), and therefore, we believe that both

changes of quantitative and qualitative nature are responsi-

ble for the observed effect.

At this point, it is not possible to say how long the meat

content in food remains perceptible in axillary odor. Nor

do we know how long one must consume meat to produce

discernible changes in body odor. Moreover, we can also

only speculate about the already perceptible amount of meat

consumed. The 2 weeks' diet period we chose for our study

was based on results of an analytical study which found com-

pounds of environmental origin in axillary odor after 10 days

of hygienic and diet restrictions (Labows et al. 1979). Future

studies should address the question of diet duration or

quantity of meat consumption and changes in body odor.

Further, it should also be tested whether the observed

effect is restricted to ''red'' meat or may be applied also

to ''white'' meat (i.e., poultry and fish).

Current knowledge allows us only to speculate what par-

ticular compounds and metabolic processes are responsible

for hedonic changes in body odor after the meat consump-

tion. We propose that it could be due to changes in amount

and/or relative abundance of aliphatic acids. The axillary re-

gion contains abundant numbers of apocrine glands produc-

ing milky secretions. Fresh apocrine secretion is odorless but

is rapidly converted by axillary microflora to odorous break-

down products. Of particular interest are corynobacteria A

as they metabolize fatty acids to short aliphatic acids (James

et al. 2004). Chromatographic examination of axillary sweat

found a number of both saturated and unsaturated and

branched and nonbranched aliphatic acids particularly of

C

5

–C

11

length (Zeng et al. 1991). If this is the case, we

may expect a correlation between the change in the odor

and fat proportion in meat.

Factors influencing axillary odor composition are of a very

complex nature. Odor similarity of twins (Wallace 1977) and

other relatives suggests that odor individuality (i.e., odor sig-

nature) is to some extent under genetic control. Recently it

was found that human raters are able to match monozygotic

twins but not dizygotic twins who lived apart in a proportion

higher than chance (Roberts et al. 2005). Influence of genetic

factors is also supported by MHC-related odor preferences

(Wedekind et al. 1995; Wedekind and Fu

¨ri 1997). Environ-

mental factors putatively shaping odor signature are nu-

merous and include eating habits, smoking, using drugs,

medicals, some diseases, and infections. Of course, we should

not forget that humans also purposely shape their olfactory

nature by using cosmetics, perfumes etc. We suggest that the

main nongenetic source of axillary odor variation in a healthy

human is due to differences in diet. Our opinion is supported

by a study which showed that hand odor of twins on different

diet was correctly matched; however, this was not true for

twins on the same diet (Wallace 1977). Hepper (1988) found

that dogs can discriminate between adult monozygotic twins

on different diets. On the other hand, the same dogs were not

able to distinguish the odor of monozygotic sucklings on the

same diet. The diet effect has also been observed in non-

human animals, for example, in guinea pigs or meadow voles

(Beauchamp 1976; Ferkin et al. 1997). Possible effects of

some food ingredients were suggested by odor researchers.

In most studies, food is controlled to avoid its putative con-

founding effect. In particular, avoidance of meals containing

garlic, onion, chilli, pepper, vinegar, blue cheese, cabbage,

radish, fermented milk products, and marinated fish is com-

monly recommended (e.g., Wedekind and Fu

¨ri 1997; Chen

and Haviland-Jones 2000; Rikowski and Grammer 1999;

Platek et al. 2001; Thornhill et al. 2003; Havlicek et al.

Table 1 Correlation coefficients between rated variables in first (1) and second sessions (2)

Pleasantness 1 Attractiveness 1 Masculinity 1 Intensity 1 Pleasantness 2 Attractiveness 2 Masculinity 2 Intensity 2

Pleasantness 1 0.98 ÿ 0.86 ÿ 0.81 0.20 0.21 0.37 ÿ0.17

Attractiveness 1 0.98 ÿ 0.82 ÿ 0.79 0.20 0.22 0.40 ÿ0.16

Masculinity 1 ÿ0.86 ÿ0.82 0.83 ÿ 0.11 ÿ 0.12 ÿ 0.33 0.13

Intensity 1 ÿ0.81 ÿ0.79 0.83 ÿ 0.23 ÿ 0.23 ÿ 0.15 0.40

Pleasantness 2 0.20 0.20 ÿ 0.11 ÿ 0.23 0.96 ÿ 0.52 ÿ0.87

Attractiveness 2 0.21 0.22 ÿ 0.12 ÿ 0.23 0.96 ÿ 0.41 ÿ0.81

Masculinity 2 0.37 0.40 ÿ 0.33 ÿ 0.15 ÿ0.52 ÿ 0.41 0.66

Intensity 2 ÿ 0.17 ÿ 0.16 0.13 0.40 ÿ 0.87 ÿ 0.81 0.66

Correlations in bold are significant at P< 0.05, N= 17. Means for odor donors served as unit of the analysis.

Effect of Meat Consumption on Body Odor 751

2006). In most cases, our knowledge of the above-mentioned

variables is based on subjective experience or anecdotal

accounts rather than on controlled studies. In fact, we know

very little about the effect of particular components and even

less about their interactions. Consumption of ''red meat,''

which may have an impact on body odor, was not controlled

in former studies. Thus, we recommend for future studies to

control or at least to check whether experimental groups do

not systematically differ in the amount of meat consump-

tion. Our results extend our knowledge of how environmen-

tal factors influence the body odor.

Supplementary material

Supplementary material can be found at http://www

.chemse.oxfordjournals.org.

Acknowledgements

We thank to all volunteers for their participation in the study, Anna

Kotrcova for help with experimental design arrangement and

manuscript corrections, Dagmar Kohoutova for helping with data

collection, and Jaroslav Flegr, Jitka Hanusova, Jindra Havlickova,

Barbara Husarova, Vera Pivonkova, Craig Roberts, and 2 anony-

mous referees for valuable advices and language corrections. We

are also grateful to Optimum Distribution CZ&SK company for

providing perfume testers for us. The study was supported by the

GAUK 393/2005 grant. The authors declare that they have no com-

peting interest and both are nonvegetarians.

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Accepted July 13, 2006

752 J. Havlicek and P. Lenochova

... In addition to enduring traits, temporary circumstances such as emotional state [22] or diet [28,29] can also be reflected in a person's body odor. Transitory states, such as illness, fertility, or sexual interest [30][31][32], can be detected through body odor. ...

... Social judgments based on body odorants are likely also informed by fragrance components, as well as underlying genetic, health, and dietary information [33]. Day-to-day body odors are influenced by dietary choices [28,29,39], leading to variability. For example, odors from monozygotic twins on different diets can be discriminated against but not if they are on the same diet [40,41]. ...

... For example, odors from monozygotic twins on different diets can be discriminated against but not if they are on the same diet [40,41]. In many studies involving body odor, food is controlled in order to avoid its potentially confounding or overwhelming effects; participants are asked to avoid strong-smelling foods, such as garlic or blue cheese [28,42]. One of the questions asked by the present study is whether food odors could act as a proxy for body odorants in triggering social judgments about gender. ...

  • Nicole L Hovis
  • Paul R Sheehe
  • Theresa Leslie White Theresa Leslie White

First impressions of social traits are regularly, rapidly, and readily determined from limited information about another individual. Relatively little is known about the way that olfactory information, particularly from scents that are not body odors, alters a first impression. Can the attributes of an odorant be conferred onto a person associated with that scent? To explore this, 101 participants were asked to form an impression of a hypothetical person based on the following stimuli: A gender-neutral silhouette, a list of six personal characteristics, and one of five odorants. Participants then rated the likelihood that the hypothetical person possessed each of 51 personality traits that were determined a priori as falling into six attribute categories. Participants also directly rated all odorants for the six categories and intensity. A T-test showed that ratings of the hypothetical person were less disparate from the odor that was presented during impression formation than from other odors. ANOVA revealed that the effects were heterogeneous, with odorants varying in their effectiveness in associating the hypothetical person with categories. The present data suggest that a hypothetical person can be imbued with the specific attributes of an odor and that some odors are better at contributing to impressions than others.

... Each person has a characteristic body odour that is a result of the emission of more than several hundred volatile organic compounds present in the breath and emitted by the skin (products of glandular secretions interacting with skin bacteria) (Roberts et al., 2005;Lenochova and Havlicek, 2008). Additional factors such as diet, overall health, or even reproductive status and endocrine system functions may also influence an individual's olfactory signal (Lindsay et al., 2000;Roberts et al., 2005;Havlicek and Lenochova, 2006). These factors are believed to be partly a cause of the observed varying degree of human attractiveness to malaria mosquitoes. ...

In a modern world, both tick-borne diseases and alcohol consumption are among major public health threats. In the present opinion article, we pose the question, whether these two health problems: alcohol consumption and tick-borne diseases prevalence can be related. We hypothesize that it is possible due to at least three factors: outdoor places chosen for alcohol consumption, behavioral changes induced by alcohol, and possible stronger attraction of human hosts after alcohol consumption to ticks. Many important clues are coming from social studies about people's preference of places to consume alcohol and from studies regarding the attraction of people consuming alcohol to mosquitos. These data, however, cannot be directly transferred to the case of alcohol consumption and ticks. Therefore, we suggest that more detailed studies are needed to better understand the possible individual attractiveness of people to ticks and ways alcohol may influence it.

... Taken together, therefore, the evidence published to date therefore supports a number of intriguing connections between personality traits and taste perception/food behaviour. Finally, here, the link between an individual's diet and their body odour should not be ignored either (see Havlicek and Lenochova, 2006;Zuniga et al., 2017). ...

  • Charles Spence Charles Spence

A number of personality characteristics have been linked to various aspects of taste (gustation), trigeminal, and olfactory perception. In particular, personality traits have been linked to olfactory sensory thresholds and olfactory identification abilities, as well as to the sensory-discriminative aspects of taste/flavour perception. To date, much of the research in this area has focused on Sensation Seeking (including Experience Seeking, and Openness to Novel Experiences), with the latter being linked to a preference for spicy, and possibly also crunchy, sour, and bitter foods/drinks. Novelty-seeking has also been linked to a preference for salty foods, while anxious individuals appear to enjoy a much narrower range of foods. A bidirectional link has also been documented between taste and mood. Certain of the personality-based differences in taste/flavour perception and food behaviour have been linked to differences in circulating levels of neurotransmitters and hormones in both normal and clinical populations. Taken together, therefore, the evidence that has been published to date supports a number of intriguing connections between personality traits and taste perception/food behaviour.

... One reason for this, although unlikely at first glance, could be that owners prefer the smell of dogs that are not fed raw meat. As Havlicek and Lenochova 31 reported in their study, women preferred the scent of men who eat a plant-based diet to that of men who consume large amounts of meat. Those results were later confirmed by Zuniga et al. 30 , who determined that women consider the scent of a man more pleasant when his diet is richer in fruits and vegetables. ...

Several studies report that olfactory cues play an important role in human life; humans are essentially able to recognize other family members and friends by their odors. Moreover, recent studies report that humans are also able to identify odors of non-conspecifics. The aim of this study was to determine whether dog owners are able to identify their dogs by smell and distinguish the odor of their own dogs from those of other dogs. A total of 53 dog owners (40 females and 13 males of different ages) volunteered to take part in this study. A number of the participants (17) owned 2 dogs; these owners took part in the study twice (i.e., working with only one dog at a time). Sterile gauze pads were used to collect odor samples from the dogs. Each pad was placed in its own sterile glass jar (750 ml) with a twist off lid until the experiment commenced. Participants were asked to identify their own dog´s odor from a line-up of 6 glass containers. This experiment demonstrated that dog owners are capable of identifying their dogs by smell on a significant level. Results of this study additionally suggested that male owners outperformed their female counterparts in the identification process. Moreover, dog owners whose dogs were housed outside had a higher success rate in identification than did participants who kept their dogs indoors with them. The dog owners found it easier to identify dogs that had been neutered, fed dry dog food and bathed less frequently. In general, younger dog owners tended to have more success when attempting to identify their dogs than did their older counterparts.

... On the other hand, some drinks and foods, such as beer and bananas, can increase human attractiveness to mosquitoes (Shirai et al., 2002;Lef evre et al., 2010;Paskewitz et al., 2018). Considering that human diet can modify the metabolic rate and the release of different odor-related volatile metabolites (Havlicek & Lenochova, 2006;Ajibola et al., 2013;Baranska et al., 2013;Zuniga et al., 2017), it is not surprising that some foods and alcoholic beverages can have an impact on the release of kairomones. However, as shown in this section, the literature on these aspects is quite scarce and further studies on the effects of diet on susceptibility to mosquitoes are needed. ...

Blood-feeding mosquitoes locate humans spatially by detecting a combination of human-derived chemical signals, including carbon dioxide, lactic acid, and other volatile organic compounds. Mosquitoes use these signals to differentiate humans from other animals. Spatial abiotic factors (e.g. humidity, heat) are also used by mosquitoes to find a host. Mosquitoes cause discomfort and harm to humans, being vectors of many pathogens. However, not all humans suffer from mosquito bites with the same frequency or intensity. Some individuals are more attractive to mosquitoes than others, and this has an important impact on the risk of infection by pathogens transmitted by these vectors, such as arboviruses and malaria parasites. Variability in human attractiveness to mosquitoes is partially due to individual characteristics in the composition and intensity in the release of mosquito attractants. The factors that determine these particularities are diverse, modestly understood and still quite controversial. Thus, this review discusses the role of pregnancy, infection with malaria parasites (Plasmodium spp.), skin microbiota, diet, and genetics in human attractiveness to mosquitoes. In brief, pregnancy and Plasmodium infection increase the host attractiveness to mosquitoes. Skin microbiota and human genetics (especially HLA alleles) modulate the production of mosquito attractants and therefore influence individual susceptibility to these insects. There is evidence pointing to a role of diet on human susceptibility to mosquitoes, with some dietary components having a bigger influence than others. In the last part of the review, other factors affecting human-mosquito interactions are debated, with a special focus on the role of mosquito genetics, pathogens and environmental factors (e.g. wind, environmental disturbances). This work highlights that individual susceptibility to mosquitoes is composed of interactions of different human-associated components, environmental factors, and mosquito characteristics. Understanding the importance of these factors, and how they interact with each other, is essential for the development of better mosquito control strategies and studies focused on infectious disease dynamics.

... While it is well known that fruits and vegetables like garlic or asparagus strongly affect the odor of breath, sweat, and urine [6], there is only minor knowledge regarding the fact that food consumption habits also affect the emotional valence of body odor. The body odor of men regularly consuming red meat is rated as being more unpleasant and more intense than body odor samples from men on a non-meat diet [7]. Similarly, the axillary odor of men consuming a diet rich in fruits and healthy vegetables, e.g., garlic, is associated with an increase in pleasantness [8,9]. ...

The current study examines neural responses to satiety- and fasting-related volatiles and their effect on the processing of body shapes. Axillary sweat was sampled with cotton pads from 10 individuals after 12 h of fasting, and after having consumed a standard breakfast. Pure cotton pads served as the control. The chemosensory stimuli were presented to 20 participants (via a constant-flow olfactometer) exclusively, and additionally as context to images of overweight and underweight avatars. EEG was recorded (61 electrodes), and chemosensory (CSERPs; P1, N1, P2, P3) and visual event-related potentials (VERPs; N1, P2, P3a, P3b) were analyzed. The amplitudes of all positive CSERP components differed more strongly from cotton in response to chemosensory satiety cues as compared to fasting cues (P1: p = 0.023, P2: p = 0.083, P3: p = 0.031), paralleled by activity within the middle frontal and temporal gyrus. Overweight compared to underweight body shapes tended to elicit larger VERP P2 amplitudes (p = 0.068), and chemosensory satiety cues amplified the VERP amplitudes in response to any body shape (P2, P3a, P3b; all ps < 0.017) as compared to the cotton control. The results indicate that chemosensory satiety cues transmit complex social information, overriding the processing of analogous visual input.

... cm×9-2 m-1ks). The day before and on the day of sampling, i.e., for about 48 h, participants were asked to avoid aromatic foods (e.g., spices, blue cheese, garlic), alcoholic beverages or other drugs, demanding physical activities (e.g., jogging), sex, and the use of fragranced products, which might all affect the quality of their body odor (Havlicek and Lenochova, 2006;Lenochova et al., 2009). Donors' conformity with these instructions was checked by a questionnaire completed when handing over the body odor samples (for the questionnaire, see Supplementary materials). ...

Previous studies have shown that women perceive male faces with a more reactive immune system as more attractive, but whether body odor might likewise provide cues to immune function has not been investigated yet. These two studies tested a possible relationship between body odor quality and immunoreactivity (Study 1) and immune system function (Study 2). In Study 1, we collected body odor samples from 21 men just before and two weeks after vaccination against hepatitis A/B and meningococcus. We determined the levels of specific antibodies (selected as markers of immune system's reactivity), testosterone, and cortisol. Subsequently, 88 female raters assessed the samples for their attractiveness, intensity, and healthiness. In Study 2, we collected body odor and blood samples from 35 men and women. We assessed key parameters of their innate and adaptive immunity, such as complement activity or total lymphocyte T and B counts and asked 95 raters to assess the samples for their attractiveness, intensity, and healthiness. In Study 1, we found no significant association between antibody levels induced by vaccination and perceived body odor attractiveness, intensity, and healthiness. We also found no significant relationship between antibody levels and steroid hormones (testosterone and cortisol). In Study 2, we likewise found no association between basal key parameters (innate and adaptive) of the immune system and body odor quality. Our results indicate that body odor does not serve as a cue to the reactivity of the immune system.

... To demonstrate an odor-mediated behavioral or physiological response in humans requires meticulous control of confounding factors, and the effect size is usually not large. Second, human secretions contain hundreds of chemical compounds that vary from person to person and time to time and are susceptible to influences from many environmental factors from diet, hygiene, to chemical products used in daily life (Penn and Potts, 1998;Havlicek and Lenochova, 2006). Highquality samples where such environmental effects are minimized are necessary for the identification of bioactive molecules or combinations of molecules that are bioactive but are very difficult to obtain and preserve. ...

Pheromones are chemicals that serve communicational purposes within a species. In most terrestrial mammals, pheromones are detected by either the olfactory epithelium or the vomeronasal organ and processed by various downstream structures including the medial amygdala and the hypothalamus to regulate motivated behaviors and endocrine responses. The search for human pheromones began in the 1970s. Whereas bioactive ligands are yet to be identified, there has been accumulating evidence that human body odors exert a range of pheromone-like effects on the recipients, including triggering innate behavioral responses, modulating endocrine levels, signaling social information, and affecting mood and cognition. In parallel, results from recent brain imaging studies suggest that body odors evoke distinct neural responses from those observed with common nonsocial odors. Two endogenous steroids androsta-4,16,- dien-3-one and estra-1,3,5(10),16-tetraen-3-ol are considered by some as candidates for human sex pheromones. The two substances produce sexually dimorphic effects on human perception, mood, and physiological arousal. Moreover, they reportedly elicit different hypothalamic response patterns in manners contingent on the recipients' sex and sexual orientation. Neuroendocrine mechanisms underlying the effects of human chemosignals are not yet clear and await future detailed analyses.

  • Madeleine Keaveny
  • Mehmet Kibris Mahmut

Anecdotal reports indicate that women dislike their partner's body odor (BO) during the breakdown of a relationship; however, whether disliking a partner's BO is associated with intentions to break up has not been empirically tested. Therefore, the aim of the current study was to investigate, for the first time, whether disliking one's partner's BOs is associated with experiencing lower commitment to a romantic relationship. Eighty participants (48 partnered, 32 single and previously partnered) completed self-report questionnaires about their current or previous romantic relationship and the amount of exposure to—and hedonic ratings of—their current or former partner's BOs. Olfactory function was also tested, and participants smelled and rated various pieces of clothing imbued with a stranger's BO. The results demonstrated that for participants who had experienced a breakup, historically higher levels of relationship commitment were associated with higher hedonic ratings of a previous partner's BOs, regardless of the type of BOs. For participants currently in a relationship, lower relationship commitment was associated with higher breakup intentions in response to smelling their partner's BOs. These preliminary results contribute evidence for the positive association between exposure to a partner's BOs and favorable hedonic appraisals of BOs; however, further research needs to be conducted in this area to investigate nuances. Lower levels of exposure to one's partner's BOs may be more indicative of relationship commitment than exposure to hedonically unpleasant BOs of one's partner. The findings are discussed with reference to their implications for interventions in relationship breakdown.

  • Xiao -Nong Zeng
  • James J. Leyden
  • Henry J. Lawley
  • George Preti George Preti

A number of studies concerning the analysis of axillary odors have assumed that the characteristic odor produced in the axillae is due to volatile steroids and isovaleric acid. Organoleptic evaluation of Chromatographic eluants from axillary extracts was employed to isolate the region in the chromatogram where the characteristic odor eluted. The odor of the dissolved eluant was eliminated when it was treated with base, suggesting that acids make up the characteristic axillary odor. Subsequent extraction of the pH-adjusted axillary extract in conjunction with organoleptic evaluation of the Chromatographic eluant, preparative gas chromatography, and analysis by GC-MS as well as GC-FTIR showed the presence of a number of C6 to C11 straight-chain, branched, and unsaturated acids as important contributors to the axillary odor. The major odor component is (E)-3-methyl-2-hexenoic acid. Three homologous series of minor components are also important odor contributors; these consist of the terminally unsaturated acids, the 2-methyl-C6 to -C10 acids and the 4-ethyl-C5 to -C11 acids. These types of acids have not been reported previously as components of the human axillary secretions and have not been proposed previously as part of the principal odor components in this area.

A survey study examining the relative importance of various social and physical traits in heterosexual attraction was conducted. Data from 198 male and female heterosexual college students revealed that women ranked body odor as more important for attraction than "looks" or any social factor except "pleasantness." Moreover, in contrast to response to fragrance use, liking someone's natural body odor was the most influential olfactory variable for sexual interest for both men and women. Men rated a woman's good looks as most desirable and as more important than any other factor except pleasantness. Sex differences in the relative ranking of several social factors were consistent with prior research.

  • Rachel Herz Rachel Herz
  • Elizabeth D. Cahill

Olfactory information is critical to mammalian sexual behavior. Based on parental investment theory the relative importance of olfaction compared with vision, touch, and hearing should be different for human males and females. In particular, because of its link to immunological profile and offspring viability, odor should be a more important determinant of sexual choice and arousal for females than for males. To test this hypothesis a questionnaire was developed and administered to 332 adults (166 males, 166 females). Subjects used a 1–7 scale to indicate how much they agreed with a series of statements concerning the importance of olfactory, visual, auditory, and tactile information for their sexual responsivity. The data reveal that males rated visual and olfactory information as being equally important for selecting a lover, while females considered olfactory information to be the single most important variable in mate choice. Additionally, when considering sexual activity, females singled out body odor from all other sensory experiences as most able to negatively affect desire, while males regarded odors as much more neutral stimuli for sexual arousal. The present results support recent findings in mice and humans concerning the relation of female preferences in body odor and major histocompatibility complex (MHC) compatibility and can be explained by an evolutionary analysis of sex differences in reproductive strategies. This work represents the first direct examination of the role of different forms of sensory information in human sexual behavior.

  • S. Kuukasjarvi

It is a long held assumption that women have concealed ovulation, which means that men do not know when women's menstrual cycles are in their most fertile phase. Recent empirical results have provided evidence that ovulation may not be totally concealed from pair-bonded males, but the generality and the mechanisms of the finding demand further study. To examine the possible adaptive value of the phenomenon, it is necessary to study whether the ability to detect ovulation is confined to males. We studied these questions in an experiment in which male and female raters rated the sexual attractiveness and intensity of T-shirts' odors worn by 42 women using oral contraceptives (pill users) and by 39 women without oral contraceptives (nonusers). Males rated the sexual attractiveness of nonusers highest at midcycle. However, female raters showed only a nonsignificant trend for this relationship. Neither sex rated attractiveness of the odors of pill users according to their menstrual cycle. The results indicate that men can use olfactory cues to distinguish between ovulating and nonovulating women. Furthermore, the contrasting results between pill users and nonusers may indicate that oral contraceptives demolish the cyclic attractiveness of odors. Together, these findings give more basis for the study of the role of odors in human sexual behavior. Copyright 2004.

It is generally accepted that short-chain (C2-C5) volatile fatty acids (VFAs) are among the causal molecules of axillary malodour. It is also widely acknowledged that malodour generation is attributable to the biotransformation of odourless natural secretions, into volatile odorous products, by axillary bacteria. However, little information is available on the biochemical origins of VFAs on axillary skin. In these studies, assay systems were developed to investigate the generation of VFAs from substrates readily available to the bacteria resident on axillary skin. Propionibacteria and staphylococci were shown to ferment glycerol and lactic acid to the short-chain (C2-C3) VFAs, acetic and propionic acid. Furthermore, staphylococci are capable of converting branched aliphatic amino acids, such as leucine, to highly odorous short-chain (C4-C5) methyl-branched VFAs, such as isovaleric acid, which are traditionally associated with the acidic note of axillary malodour. However, in vitro kinetic data indicates that these pathways contribute less to axillary VFA levels, than fatty acid biotransformations by a recently defined sub-group of the Corynebacterium genus, coryne-bacteria (A). The results of these studies provide new understanding on the biochemical origins of VFA-based axillary malodour which, in turn, should lead to the development of novel deodorant systems.

  • Dustin J. Penn Dustin J. Penn

Individuals in some species prefer mates carrying dissimilar genes at the major histocompatibility complex (MHC), which may function to increase the MHC or overall heterozygosity of progeny. Here I review the evidence for MHC-dependent mating preferences from recent studies, including studies on the underlying olfactory mechanisms and evolutionary functions. Many studies indicate that MHC genes influence odour, and some work is beginning to examine the potential role of MHC-linked olfactory receptor genes in mating preferences. MHC-dependent mating preference increases the MHC-heterozygosity of progeny, which is suspected to confer resistance to infectious diseases. In humans, heterozygosity at MHC loci is associated with increased resistance to hepatitis and HIV infections, but experimental evidence for the heterozygote advantage hypothesis has been lacking. Here I re-analyse data from previously published experimental infection studies with mice. I show that although overdominance is rare, resistance is often dominant, suggesting that heterozygotes are often protected. A second (nonmutually exclusive) possibility is that MHC-disassortative mating preferences promotes inbreeding avoidance. This hypothesis is supported by recent evidence that MHC genes play a role in kin recognition, and that mating with close kin has rather deleterious fitness consequences. In conclusion, I discuss other ways that MHC genes might influence sexual selection. The research on MHC-mediated mating preferences is integrating the study of animal behaviour with other seemingly disparate fields, including sensory biology and immunogenetics.

Females of a number of primate species display their fertile period by behavioural and/or morphological changes. Traditionally, the fertile period in human females has been considered to be concealed. However, this presumption has rarely been tested. One of the possible mechanisms for assessing menstrual cycle phase is through the sense of smell. In this study possible changes in odour across the menstrual cycle were investigated. Samples of body odour were acquired from 12 women (aged 19–27 yr), none of whom were using hormonal contraceptives. Samples were collected using cotton pads worn in the armpit for 24 h, from the menstrual, follicular and luteal cycle phases. Our experimental sample of 42 males (age 19–34 yr) repeatedly rated these odour samples for their intensity, pleasantness, attractiveness and femininity. Raw subjective smell ratings from each man were transformed to z-scores. Subsequently, these z-scores were tested by the general linear mixed-model analysis (PROC MIXED, SAS) with the female's ID nested within the subject's ID as a random factor to account for the repeated measures of the subjects. Significant changes across the cycle were found for ratings of pleasantness [F(2,689) = 702; p = 0.001], attractiveness [F(2,546) = 6.35; p = 0.002] and intensity [F(2,530) = 3.57; p = 0.028]. Odour from women in the follicular (i.e. fertile) phase was rated as the least intense and the most attractive. Subsequent post hoc analysis revealed significant differences in intensity, pleasantness and attractiveness between the menstrual phase and the follicular phase, and in pleasantness and attractiveness between the menstrual and luteal phases. Significant difference between the follicular and the luteal phase was found only for attractiveness. Our results suggest that men can potentially use smell as a mechanism for monitoring menstrual cycle phase in current or prospective sexual partners. Therefore, the fertile period in humans should be considered non-advertized, rather than concealed.

  • Richard H. Porter
  • John D. Moore

T-shirts worn by individual children were correctly identified by the siblings and mothers of those children through olfactory cues alone. Furthermore, parents correctly distinguished between the odors of otherwise identical shirts worn by two of their own children. Bodily odors may therefore be salient stimuli for kin recognition among humans.

  • Michael H Ferkin Michael H Ferkin
  • Evan S. Sorokin
  • R. E. Johnston
  • C.J LEE

The diet consumed by animals can influence their physical condition and potential for reproductive success. Do differences in diet quality affect the attractiveness of secondary sexual characteristics to the opposite sex? This study addressed this question by examining the attractiveness of odours produced by meadow voles,Microtus pennsylvanicusthat were fed diets that differed in protein content. Meadow voles that served as scent donors were maintained on one of three diets, consisting of 9, 15 or 25% protein, all of which are sufficient to maintain voles in reproductive condition. These diets influenced the attractiveness of all three odours tested (anogenital area, urine and faeces). Both male and female subjects preferred odours from donors on high-protein diets: subjects preferred odours of opposite-sex conspecifics fed a 15 or 25% protein diet over odours from donors fed a 9% protein diet. Females preferred two odours of males on a 25% protein diet over the same odours of males on a 15% protein diet. These results suggest a mechanism for mate choice via odour preferences based on the protein content of the food consumed by potential partners. Because animals compete for access to higher-quality diets in nature, the choice of a mate with a high-quality diet may also be a means of choosing a higher-'quality' individual.

  • Patricia Wallace

Both men and women observers were able to discriminate between two women, two men, and a man and a woman, on the basis of olfactory cues from the hand. The accuracy of female observers was improved when the two stimulus individuals were genetically unrelated, and when they were on different diets.