![Mean ratings (˙ SE) of 16 pairs of axillary odors on pleasantness, attractiveness, and intensity in the experimental (garlic) condition (gray bar) and control (non-garlic) condition (brown bars) by 40 women. Ratings were on 7-point scale (e.g., 1-very unpleasant and 7-very pleasant). Asterisks indicate level of significance in paired t-tests. p < 0:05 level; p < 0:01 level (after Fialová et al. [50.39])](https://www.researchgate.net/profile/Jitka-Fialova-2/publication/314134477/figure/fig2/AS:667791430537225@1536225292269/Mean-ratings-SE-of-16-pairs-of-axillary-odors-on-pleasantness-attractiveness-and_Q320.jpg)
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Individual Va
949
Part F | 50
50. Individual Variation in Body Odor
Jan Havlíček, Jitka Fialová, S. Craig Roberts
Humans produce numerous volatile compounds
from dierent areas of the body, either as a di-
rect result of metabolic processes or indirectly via
metabolism of resident microora. Body odors vary
between individuals, partly due to genetic dier-
ences, but odors of the same individual also vary
across time due to environmental inuences. We
discuss how at least part of the genetic inuence
appears to be related to certain personality charac-
teristics and to sexual orientation. We then review
the current state of the art in terms of intraindivid-
ual variation, including eects of intrinsic factors,
such as hormonal inuences on body odor and
environmental factors, namely eects of diet and
certain diseases. Some of these changes can be
perceived by other individuals and might there-
fore provide social cues of current motivational,
nutritional, and health status. Finally, we discuss
. Personality ..........................................
. Sexual Orientation ...............................
. Hormonal Inuences............................
. Diet ....................................................
. Diseases and Disorders.........................
.. Metabolic Disorders ...................
.. Infectious Diseases ....................
.. Tumors .....................................
.. Psychiatric Disorders..................
. Conclusion...........................................
References...................................................
how specic odor proles associated with certain
infectious diseases and metabolic disorders can be
used as a cheap and ecient medical screening
tool.
In common with other animals, humans constantly pro-
duce a cloud of volatile chemicals which can poten-
tially be perceived by others. The majority of these
compounds are direct by-products of body metabolism
or products of the metabolism of either commensal or
pathogenic microflora. Human body odors are emit-
ted from various areas of the body notably from the
mouth, the anogenital region, the scalp, and the axillae.
In healthy adults, axillary odor appears to be the most
distinctive, due to a relatively high concentration of both
eccrine and apocrine glands in this area. Interestingly,
most compounds in fresh apocrine sweat are odorless
and these are converted to odoriferous molecules by the
action of the residential bacterial microflora (Chap. 48).
Body odor appears to be individually specific and rel-
atively stable [50.1], perhaps due to genetic influences.
This is supported by three lines of evidence:
1. Body odor of monozygotic twins show high resem-
blance [50.2].
2. Unacquainted individuals can match relatives (e.g.,
offspring and parents) based solely on body odor
[50.3].
3. People show odor preferences associated with the
genes of the major histocompatibility complex
[50.4].
Further, people can identify others based on their
body odor (for details of this kind of evidence, see
Chap. 51). Apart from genetic influences, there are also
numerous intrinsic and extrinsic factors shaping indi-
vidual variation in human body odor. Here, we first
review two factors contributing to interindividual odor
variation, namely personality factors and sexual orien-
tation. We then turn our attention to intrinsic factors
of intraindividual variation in body odor, namely hor-
monal influence (emotion-related fluctuations in body
odor are reviewed elsewhere; see Chap. 49), and to
environmental factors, such as effects of diet and
disease.
Part F | 50.3
950 Part F Human Body Odor, Chemo-Communication and Behavioral Implications
50.1 Personality
People tend to spontaneously attribute a range of psy-
chological characteristics to others based simply on
their appearance or on thin slices of their behavior.
At least in some characteristics, such attributions are
to some extent accurate; that is, they correlate with
the target’s personality profile. These attributions have
been described as having a kernel of truth [50.5, 6].
Although less well-known, body odor could also con-
tribute to such attributions based on first impression,
as some personality traits are correlated with social
perception of body odor. For example, women in the
fertile phase of their menstrual cycle find the axillary
odor of relatively dominant men more attractive [50.7],
and in a series of studies it was recently shown that
strangers can accurately attribute levels of neuroticism
and dominance in others based solely on their axillary
odor with women showing more accurate judgments
compared to men [50.8,9]. Furthermore, prepubertal
children can accurately judge neuroticism [50.10]. The
precise mechanism responsible for the association be-
tween personality traits and axillary odor quality is not
well understood. In the case of dominance, both traits
may be underpinned by levels of testosterone. The pic-
ture might be more complex in the case of neuroticism,
but a potential indication lies in the observation that
some emotional states (anxiety) have impact on odor
quality and in turn affect other people exposed to such
odors [50.11, 12]; as neurotic individuals tend to be
more frequently distressed, this might also affect their
body odor.
50.2 Sexual Orientation
The effects of one’s sexual orientation extend beyond
the sex of preferred romantic partners. There is ro-
bust evidence that it also influences various psycho-
logical (e.g., verbal fluency [50.13]) and morpholog-
ical characteristics (e.g., second to fourth digit ratio,
which is considered a marker of prenatal exposure
to testosterone [50.14]), perhaps due to shared bio-
logical machinery, such as prenatal exposure to the
level of androgens [50.15]. Several studies have con-
sequently tested whether sexual orientation also has an
impact on the quality of body odor, although results of
these studies are somewhat inconsistent. In one study,
odor samples taken from both heterosexual and homo-
sexual men and women were judged for pleasantness
by groups of heterosexual and homosexual men and
women. There was a complex pattern of significant
between group differences, although one relatively con-
sistent pattern emerged: All groups except homosexual
men showed lower preference for the odor of homosex-
ual men [50.16]. In contrast, anotherstudy, which tested
only the preferences of heterosexual women, reported
that they found the odor of homosexual men more, not
less, appealing than those of heterosexual men [50.17].
We therefore await further research before being able
to draw sharp conclusions on this fascinating topic.
Furthermore, the underlying mechanism linking sexual
orientation and the quality of body odor is currently un-
known.
50.3 Hormonal Inuences
The endocrine system controls a very wide range of
physiological processes and contributes to the motiva-
tion systems. Hormonal action can thus also influence
body odor quality, either as a by-product of hormonal
metabolism or by metabolism of the affected tissue.
Furthermore, hormonal action might also target the
apocrine glands in order to directly communicate mo-
tivational state to other individuals. The main focus of
research on endocrine influences on body odor has been
on steroid hormones.
In women, for example, there is relatively robust
evidence showing that attractiveness of axillary body
odor rated by men varies across the menstrual cycle,
peaking in the follicular phase when the probability
of conception is highest [50.18, 19]. No such changes
are observed in women using hormonal contracep-
tion, suggesting that this effect is steroid hormone
dependent [50.20], presumably as a result of chang-
ing amounts or ratios of estrogen and progesterone.
One early study also found significantly higher pleas-
antness of vaginal odor in the follicular phase of the
cycle [50.21]. Although the magnitude of these cyclic
changes is substantially lower than the differences in
odor attractiveness among individual women [50.22],
they are nonetheless perceivable and might play a role
in coordinating sexual activity. In line with this idea,
Individual Variation in Body Odor 50.4 Diet 951
Part F | 50.4
men exposed to women’s axillary odors collected dur-
ing the fertile phase of the cycle experience elevated
levels of testosterone [50.23,24] although another study
was not able to replicate this effect [50.25]. Similar in-
creases in testosterone and cortisol are invoked by vul-
var odor collected in the women’s fertile phase [50.26].
In a series of follow-up studies, it was found that expo-
sure to fertile phase axillary odors specifically activates
mating-related concepts in men (e.g., generating more
sexually tinged words), increases their judgments of
women’s sexual arousal, and leads to more risky de-
cisions (assessed by a computerized blackjack card
game) [50.23]. Furthermore, women seem to be simi-
larly reactive to fertility-related odors as they showed
increased testosterone levels after exposure, although
this is presumably a consequence of intrasexual com-
petition rather than attraction [50.27].
One might also expect changes in body odor related
to pregnancy, based on the specific hormonal profiles
which occur during this time. This includes elevated
levels of human chorionic gonadotropin during the first
trimester and continuouslyrising levels of progesterone
and estrogens during the course of pregnancy. In one
study, several specific compounds were detected in ax-
illary and areolar samples taken from pregnant women.
Some of these were also found in lactating women af-
ter delivery, but not in a control group of nonpregnant
women. Two of the identified chemicals, 1-dodecanol
and oxybis octane, showed systematic fluctuations dur-
ing the pregnancy [50.28]. Furthermore, changes in
breath volatiles of pregnant women have been found us-
ing an electronic nose, although no specific compounds
related to pregnancy were identified [50.29]. These an-
alytical results are also supported by subjective ratings,
such that men rate axillary odor of women in the second
trimester as most pleasant [50.30]. Finally, several stud-
ies on attractiveness of human body odor to mosquitoes
showed higher bite rates in pregnant women [50.31–
33]. Interestingly, the attractiveness of body odors to
mosquitoes appears to be affected by levels of short-
chain fatty acids, and this might explain higher bite
rates observed in pregnant women [50.34].
In contrast, investigations into potential links be-
tween the quality of body odor and levels of other
hormones present more inconsistent results. In one
study, it was found that attractiveness of axillary body
odor is positively associated with cortisol levels but
not with testosterone [50.35]. Another study, based
on a larger sample of both odor donors and raters,
showed that males whose odor samples were judged as
attractive show higher levels of testosterone but not cor-
tisol [50.36]. Finally, one more study found a negative
association with cortisol levels [50.37]. Thus, clearly
it is currently difficult to draw any robust conclusions
on relationships between these steroid hormones and
odor, and further investigations of potentially modulat-
ing factors responsible for these inconsistent findings
are required.
50.4 Diet
Some authors consider diet as the most salient envi-
ronmental factor shaping our body odor as humans
consume a high variety of aromatic foods [50.38]. Sev-
eral volatile compounds may subsequently emanate in
breath odor. Further, some components of the diet might
produce volatile compounds only after being metabo-
lized by the digestive system. As volatile molecules are
relatively small, they can pass through the epithelium
and be distributed across the body via the blood stream.
In this way, they can consequently affect axillary odor
or odor of urine and feces. The studies on effect of diet
are summarized in Table 50.1.
Evidence from animal studies indicates that diet
might be a potent modulator of body odor and that
in some species, females can use odor cues to as-
sess the quality of potential mates by the quantity and
quality of ingested food. Pierce and Ferkin [50.49] in-
vestigated the effect of food deprivation on odor of
female meadow voles (Microtus pennsylvanicus). It was
shown that the odor of starving animals was less at-
tractive compared to individuals fed ad libitum.This
effect disappeared 48 h after re-feeding. The crucial fac-
tor for nutrition appears to be not only the availability
of food, but also its quality, such as the amount of di-
etary protein. It was found that both male and female
meadow voles preferred the odor of opposite-sex indi-
viduals on a high-protein diet, and spent the least time
investigating the odor of individuals on a low protein
diet [50.50]. Similarly, attractiveness of urine odor was
positively linked to high quality food in guinea pigs
(Cavia porcellus) [50.51]. In an analogous manner, red-
backed salamander (Plethodon cinereus) females assess
territory quality by examination of male fecal pellets
and prefer pellets from individuals fed on high-quality
food [50.52]. Other social interactions might be affected
by diet as well. For instance, in spiny mouse (Acomys
cahirinus) pups, preferences are formed early in life,
and they subsequentlyprefer the odor of females fed on
the same diet as their mothers [50.53].
The effect of diet on human body odor was first
demonstrated in twin studies. Humans were able to
discriminate the hand odors of monozygotic twins on
Part F | 50.4
952 Part F Human Body Odor, Chemo-Communication and Behavioral Implications
Tab l e 5 0.1 Summary of studies on effect of diet on human bodily odors
Auth ors Food Odor source Odor quality/hedonicity Volatile compound(s)
Fialová
et al. [50.39]
Garlic Axilla "Attractiveness, pleasantness,
#intensity
Hauser
et al. [50.40]
Amba
(mango, saffron, curry)
Skin, amni-
otic fluid
Foul, curry
Hauser
et al. [50.40]
Khilba
(fenugreek)
Skin Fenugreek
Hauser
et al. [50.40]
Shug
(cumin, garlic, salt, oil,
pepper)
Skin Cumin
Havlíˇcek
and Leno-
chova [50.41]
Red meat Axilla "Attractiveness, pleasantness,
#intensity
Korman
et al. [50.42]
Hilbe (fenugreek) Skin, urine Maple syrup 3-hydroxy-4,5-dimethyl-
2(5H)-furanone (sotolone)
Lefèvre
et al. [50.43]
Beer Skin "Attractiveness to malarial mosquitoes
(Anopheles gambiae)
Pelchat
et al. [50.44]
Asparagus Urine Sulfurous, cooked cabbage Methanethiol, carbon disulfide,
dimethyl disulfide, dimethyl
sulfide,
dimethyl sulfone, dimethyl
trisulfide,
S-methyl-2-propenthioate
Suarez
et al. [50.45]
Pinto beans,
lactulose
Flatus Rotten eggs, decomposing vegetables,
sweet
Hydrogen sulfide,
methanethiol, dimethyl sul-
fide, hydrogen sulfide
Suarez
et al. [50.46]
Garlic Breath Garlic Hydrogen sulfide,
methanethiol,
allyl mercaptan, allyl methyl
sulfide,
allyl methyl disulfide,
allyl disulfide
Tam a k i
et al. [50.47]
Garlic Breath Garlic Methanethiol, dimethyl sulfide,
allylthiol, allyl methyl sulfide,
dimethyl disulfide, methyl
propyl sulfide,
diallyl disulfide, 3-(allylthio)
propionic acid
Yalcin
et al. [50.48]
Fenugreek Skin, urine Maple syrup 3-hydroxy-4,5-dimethyl-
2(5H)-furanone (sotolone)
a different diet, but their performance was not higher
than chance when assessing odor of twins on the same
diet [50.54]. This task appears to be too difficult even
for trained dogs. They successfully discriminated be-
tween the odors of both dizygotic and monozygotic
twins on different diets, but not the odors of monozy-
gotic twins on the same diet [50.55].
Perhaps predictably, the main source of bodily
odors that is affected by diet is breath odor. Breath
malodor could have a profound impact on everyday so-
cial interactions [50.56] as numerous volatiles emanate
from consumed food due to mastication and digestive
processes in both the oral cavity and the stomach. Nev-
ertheless, only some parts of the diet produce specific
odor profiles. Garlic odor would be a representative ex-
ample. It has been demonstrated that the typical garlic
odor in breath is more intense after ingestion of raw
garlic compared to cooked garlic [50.47]. The char-
acteristic odor consists of distinctive sulfur-containing
compounds (allicin, mono-, di- and trisulfides, ajoene,
and vinyldithiines). Moreover, this odor lasts for several
hours even despite oral hygiene, especially due to the
unique derivation of allyl methyl sulfide from the gut.
Thus, garlic breath initially originates from the mouth
and subsequently from the gut [50.46].
Another source of bodily odors originates from
digestive processes. Action of bacteria on endoge-
nous sources produces gases within the digestive sys-
tem [50.57]. These eventually emerge as flatus thatcon-
sists of both nonodorous compounds, such as oxygen,
Individual Variation in Body Odor 50.4 Diet 953
Part F | 50.4
Fig. 50.1 An odor sample rating session (courtesy of J. Fi-
alová)
nitrogen, carbon dioxide, hydrogen and methane, and
odorous ones containing sulfur, the production of which
could be affected by dietary habits [50.45]. Higher lev-
els of sulfur occur in some breads, dried fruits, brassicas
and soy flour. A study where flatulence was increased
in participants due to consumption of pinto beans and
lactulose found that flatus malodor correlates with the
concentration of hydrogen sulfide (reminiscent of rot-
ten eggs) and methanethiol (decomposing vegetables)
[50.58]. Similarly, urine of people who have recently
eaten asparagus has an unusual sulfurous odor similar
to cooked cabbage [50.44].
Several case studies show that the mother’s diet
might also affect the body odor of the newborn baby.
For instance, in one case, a newborn baby had body
odor and urine that smelled of maple syrup. The baby
was therefore suspected of having maple syrup syn-
drome, but subsequent laboratory tests did not confirm
this diagnosis. It was subsequently discovered that,
prior to delivery, the mother ate fenugreek-spiced food
which was responsible for this distinctive odor [50.42,
48]. The maple syrup odor that appears after fenugreek
consumption was recently analyzed and several com-
pounds which could be responsible for the distinctive
odor were found in human sweat [50.59]. The same
odor may also be detected exuding from the mother’s
skin and may be transmitted to the infant via the
mother’s breast milk [50.42]. In other cases, the mother
consumed shug (a dish containing cumin, garlic, salt,
Control
Garlic
Pleasantness
**
*
*
Attractiveness Intensity
Mean rating score
5
4.5
4
3.5
3
2.5
2
Fig. 50.2 Mean ratings (˙SE) of 16 pairs of axillary
odors on pleasantness, attractiveness, and intensity in the
experimental (garlic) condition (gray bar) and control
(non-garlic) condition (brown bars)by40women.Rat-
ings were on 7-point scale (e.g., 1 – very unpleasant and
7 – very pleasant). Asterisks indicate level of significance
in paired t-tests. p<0:05 level; p<0:01 level (after
Fialová et al. [50.39])
oil, and pepper) and her baby consequently smelled of
cumin. In a similar way, a newborn baby and its am-
niotic fluid was found to be yellowish, with an odor
reminiscent of curry, after the mother ate amba,which
consists of mango, saffron, and curry [50.40].
The evidence on the effects of the diet on axillary
odor is comparatively limited. One study [50.41] inves-
tigated whether consumption of red meat affects human
body odor, because people from some predominantly
vegetarian cultures say that people who eat meat smell
bad because of it. The results of the study showed that
the axillary odor of individuals on a nonmeat diet was
perceived as more attractive, more pleasant, and less in-
tense than the odor of the same individuals on a diet
containing meat (at least one meat dish daily for 2
weeks). These results might appear counterintuitive, as
meat consumption is thought to play a significant role
in human evolution, and because they might be at odds
with studies on effects of high protein diets in rodents
(see above). The explanation may be that the amounts
of meat consumed in contemporary populations, and in
Havlicek and Lenochova’s experiment, may be higher
than would normally be experienced in traditional or
ancestral societies. In this way, body odor changes af-
ter consumption of relatively large quantities of meat
could in fact resemble a metabolic disorder [50.41].
Another surprising finding resulted from a series of
studies that examined the effects of garlic consump-
tion on axillary odor. Samples of body odor from the
same individualswere obtained in both an experimental
Part F | 50.5
954 Part F Human Body Odor, Chemo-Communication and Behavioral Implications
(high garlic consumption) and control condition. Axil-
lary odor of the participants after ingesting garlic was
perceived as more attractive, more pleasant, and less
intense (Fig. 50.1). In contrast to the effects of garlic
on breath odor, the positive influence on axillary odor
might be explained by longer term health benefits of
garlic consumption, including antioxidant action and
antibacterial activity [50.39] (Fig. 50.2).
Interestingly, dietary effects might also affect at-
tractiveness of human body odor to blood sucking
insects. Lefèvre et al. [50.43] found that beer consump-
tion increases human odor attractiveness to malarial
mosquitoes (Anopheles gambiae). Exposure to the body
odor of participants who consumed beer caused an in-
crease in mosquito activation (take-off and up-wind
flight) and orientation (flying toward volunteers’ odors).
50.5 Diseases and Disorders
The profile of volatile compounds found in human
body odor can be affected by health and disease. This
was recognized by ancient medical authorities, such as
Hippocrates, Galen, and Ibn Sina, who advocated the
use of olfaction in medical diagnostics. Recent tech-
nological advances and availability of highly sensitive
techniques like gas chromatography-mass spectrome-
try (GC-MS) makes volatile compounds an increasingly
significant part of early disease diagnostics. Generally,
such changes in body odor might be either a result of
altered metabolism and/or more direct effects of in-
fectious agents. For this reason, metabolic disorders
and infectious diseases are reviewed separately in the
following paragraphs, where we present some represen-
tative examples of the effects of disease on body odor
(Table 50.2).
50.5.1 Metabolic Disorders
The main cause of metabolic disorders is deficiency in
enzymes or transport systems. Such deficiencies fre-
quently lead to the accumulation of specific metabolites
and in some disorders, to its further conversion to other
compounds. If these are volatile, the metabolite or its
products may lead to a characteristic odor profile in af-
fected individuals. These metabolic disorders are often
a consequence of simple Mendelian inheritance.
Isovaleric Acidemia
The disorder is caused by a deficiency of the isovaleryl-
CoA dehydrogenase, which is involved in leucine
metabolism. Due to the disorder, isovaleric acid accu-
mulates in the tissues and leads to serious ketoacidosis
which may subsequently result in coma [50.83]. Pa-
tients with isovaleric acidemia produce high levels of
isovaleric acid in body fluids and urine, which is char-
acterized by the distinctive odor of sweaty feet [50.64].
Maple Syrup Urine Disease
This is an autosomal recessive inherited disorder caused
by deficiency in the enzyme 2-oxo acids dehydroge-
nase complex, which results in the accumulation of
branched-chain amino acids, such as leucine in tis-
sues and body fluids [50.84]. If not recognized early
after birth and treated by a branched-chain amino-acid-
free diet, the disorder can result in mental retarda-
tion. Body odor and urine odor of affected individu-
als smell relatively pleasant, resembling maple syrup.
The compound responsible for the odor appears to
be sotolone (3-hydroxy-4,5-dimethyl-2(5H)-furanone)
[50.63].
Phenylketonuria
This disorder is caused by a recessive mutation in a gene
coding for phenylalanine hydroxylase. The enzyme is
expressed in liver tissue where it converts the amino
acid phenylalanine into tyrosine. Due to the phenylala-
nine hydroxylase deficiency, the phenylalanine is con-
verted to phenylpyruvic acid and phenylacetate which
are excreted in sweat and urine. The phenylacetate gives
affected individuals a musty odor, resembling sweaty
lockers [50.61].
Trimethylaminuria
The disorder is characterized by a deficiency of the
flavin containing monooxygenase 3 which converts
trimethylamine to trimethylamine N-oxide. Trimethy-
lamine is produced by gut bacteria from choline rich
food, such as eggs or legumes. In unaffected individ-
uals, most of the odorous trimethylamine is converted
in hepatic tissue to odorless trimethylamine N-oxide.
However, in people suffering from trimethylaminuria,
trimethylamine emanates from their breath, sweat, and
urine, with an odor which resembles that of decaying
fish [50.60].
Diabetes
An example of a metabolic disorder with an etiology
involving multigenetic as well as environmental fac-
tors (e.g., dietary habits) is diabetes. Type I diabetes
is characterized by insufficient secretion of insulin, and
the lack of insulin leads to an increase in the level of
ketones including acetone in the blood. As a conse-
quence, people suffering from diabetes with elevated
Individual Variation in Body Odor 50.5 Diseases and Disorders 955
Part F | 50.5
Tab l e 5 0.2 Summary of studies on disease-related body odors
Auth ors Disease/Disorder
(Pathogenic agent)
Pathology/Symptoms Odor source Odor quality Volatile compound(s)
Metabolic disorders
Chalmers et al. [50.60] Trimethylaminuria #Flavin monooxygenase 3 Breath, sweat,
urine
Decaying fish Trimethylamine
Cone [50.61] Phenylketonuria #Phenylalanine hydroxylase Sweat, urine Musty, wolf-like, barny,
sweaty locker-room towels
Phenylpyruvic acid
Laffel [50.62] Diabetes #Insulin secretion Breath Sweet Ketones (acetone)
Podebrad et al. [50.63] Maple syrup urine disease #2-oxo acids dehydrogenase Skin, urine Relatively pleasant, maple
syrup like
3-Hydroxy-4,5-dimethyl-
2(5H)-furanone (sotolone)
Tanaka et al. [50.64] Isovaleric acidemia #Isovaleryl-CoA dehydroge-
nase
Urine Sweaty feet "Isovaleric acid and its deriva-
tives
Infectious diseases
Anderson et al. [50.65]
Landers et al. [50.66]
Wol r a t h et al. [50.67]
Bacterial vaginosis (Gram-
negative bacteria Gardnerella
vaginalis, Mycoplasma)
Abnormal vaginal discharge
(color, consistency, amount),
itching, burning, dysuria
Vagina Cheesy, fishy, foul Trimethylamine
Finlay et al. [50.68] Skin ulcers (Bacteroides,
Propionibacterium)
Cutaneous lesions Skin Offensive, foul
Garner et al. [50.69] Cholera (Vibrio cholera) Watery diarrhoea, vomiting,
dehydration
Feces Sweetish Dimethyl disulfide, p-menth-1-
en-8-ol
Honig et al. [50.70] Scarlet fever (Streptococcus
pyogenes)
Red-colored rash on the body,
sore throat and fever
Skin, breath Foul
Liddell [50.71] Typhoid fever (Salmonella
typhi)
High fever, drenching sweat,
gastroenteritis
Skin Baked brown bread
Part F | 50.5
956 Part F Human Body Odor, Chemo-Communication and Behavioral Implications
Tab l e 5 0.2 (continued)
Auth ors Disease/Disorder
(Pathogenic agent)
Pathology/Symptoms Odor source Odor quality Volatile compound(s)
Phillips et al. [50.72],
Syhre and Chambers [50.73]
Syhre et al. [50.74]
Tuberculosis (Mycobacterium
tuberculosis)
Cough, chess pain, weight loss,
fever, night sweats
Breath Foul Methyl nicotinate, methyl
phenylacetate, methyl
p-anisate, o-phenylanisole,
cyclohexane, benzene
derivatives, decane, heptane
Shirasu and Touhara [50.75] Diphtheria (Corynebacterium
diphtheriae)
Sore throat, fever, difficulty
breathing
Breath Sweetish, putrid
Tumo r s
Jobu et al. [50.76] Bladder Urine Ethylbenzene, nonanoyl chlo-
ride, dodecanal, (Z)-2-nonenal,
5-dimethyl-3(2H)-isoxazolone
Phillips et al. [50.77] Lung Breath Alkanes, alkane and benzene
derivatives, isoprene, benzene
Phillips et al. [50.78] Breast Breath 2-propanol, 2,3-dihydro-1-
phenyl-4(1H)-quinazolinone,
1-phenyl-ethanone, heptanal,
isopropyl myristate
Psychiatric disorders
DiNatale et al. [50.79]
Phillips et al. [50.80]
Phillips et al. [50.81],
Smith et al. [50.82]
Schizophrenia Hallucinations,
delusions, cognitive deficit
Breath Peculiar, unpleasant Trans-3-methyl-2-hexenoic
acid, carbon disulfide, pentane
Individual Variation in Body Odor 50.5 Diseases and Disorders 957
Part F | 50.5
ketones produce acetone from their breath, which gives
off a characteristic sweet smell [50.62].
50.5.2 Infectious Diseases
The pathogenic activity of many infectious agents also
produces various volatile compounds which are emit-
ted from skin, breath, sweat, vaginal fluid, urine, and
feces. In contrast to odor-producing metabolic disor-
ders, which are frequently characterized by specific
volatile molecules with distinctive odor as we have just
described, effects on odor of patients with infectious
diseases are more complex and therefore more chal-
lenging to characterise. This can be attributed to three
main reasons:
1. Bacteria of one strain/species may metabolize dif-
ferent substrates producing a complex mixture of
volatiles.
2. Different bacteria overlap in the specific volatiles
they produce.
3. Some diseases are frequently characterized by mul-
tiple infections which may lead to less characteristic
odor.
Several infections of the digestive system are char-
acterized by distinctive fecal odor. This involves in-
fection by Vibrio cholerae which causes acute watery
diarrhoea with a distinctive sweetish odor. The volatile
compounds responsible for the odor were identified as
p-meth-1-en-8-ol and dimethyl disulfide [50.69].
Infections of the respiratory system frequently af-
fect breath odor. For instance, people suffering from
lung tuberculosis, caused by infection with Mycobac-
terium tuberculosis, are reported to have foul breath
odor. A specific mixture of volatile compounds was re-
ported from the breath of infected patients, with a sim-
ilar volatile profile found in in vitro cultures [50.73].
The biomarkers of tuberculosis infection were proposed
to be nicotinic acid, cyclohexane and some benzene
derivatives [50.72, 74]. Similarly, individuals infected
with Corynebacterium diphtheriae are characterized by
sweetish and putrid breath odor, resulting from effects
of the diphtheria-causing bacteria on the upper respira-
tory system, generating other symptoms including sore
throat and swollen tonsils [50.75].
The vagina is a major source of body odor in adult
women. It is rich in residential microflora which play
a part in odor production. Changes in vaginal odor
might reflect infection by pathological agents and it is
frequently used by gynecologists in differential diag-
nostics [50.65]. For instance, bacterial vaginosis is fre-
quently accompanied by a cheesy or fishy odor which
is caused by the production of highly odorous trimethy-
lamine [50.67]. Women diagnosed for an infection by
the protist Trichomonas vaginalis also frequently com-
plain about malodor [50.66].
Perhaps most common are changes in skin odor
caused by infections. These may derive from infec-
tion in other parts of the body, such as infection of
the intestinal tract by Salmonella typhi, the agent of
typhoid fever. People suffering from typhoid fever are
said to smell like baked bread [50.71]. Infections di-
rectly affecting the skin include scarlet fever caused by
Streptococcus pyogenes. The disease manifests in the
form of a rash, strawberry-colored tongue, and fever,
but patients also emit a distinctive foul odor from their
skin and breath [50.70]. An offensive smell isalso asso-
ciated with anaerobic infections (e.g., by Bacteroides,
Propionibacterium) which cause skin ulcers. Patients
often complain about the strong smell which can be
significantly reduced by cutaneous application of me-
tranidazol [50.68].
50.5.3 Tumors
Oncological disorders are characterized by abnormal
cell growth, mostly caused by mutations in genes (or
epigenetic factors) controlling for cellular growth and
division. However, neoplasia might be caused by vari-
ous genes and further development depends on affected
tissue. Nevertheless, affected cells might show spe-
cific metabolic changes, partly attributable to oxidative
stress, and production of distinctive patterns of volatile
molecules. Recently, there has been increased interest
in the analysis of various substances in patients with dif-
ferent carcinomas. Air exhaled by individuals with lung
cancer form a specific pattern of volatile molecules in-
cluding alkanes, alkane derivatives, and benzene deriva-
tives [50.77]. Similarly, people diagnosed with breast
cancer emanate a specific profile of volatiles in their
breath. Five biomarkers for breast cancer have been
detected including 2-propanol, heptanal, and isopropyl
myristate [50.78]. In addition, the urine of people suf-
fering from bladder cancer and prostate cancer has been
analyzed. Volatile metabolites reported to be related to
bladder cancer include dodecanal, 2-nonenal, and ethyl-
benzene [50.76]. The specific odor profile associated
with several carcinomas has been confirmed by stud-
ies using dogs as cancer detectors. Dogs can be trained
to differentiate between breath or urine odor samples
taken from people suffering from lung, bladder, and
prostate cancer [50.85].
50.5.4 Psychiatric Disorders
For a long time, it has been noted by psychiatric hospital
personnel that certain psychiatric conditions can be as-
Part F | 50.6
958 Part F Human Body Odor, Chemo-Communication and Behavioral Implications
sociated with a peculiar odor. Schizophrenia, in partic-
ular, has attracted most attention. Early studies claimed
to identify trans-3-methyl-2-hexenoic acid as a reliable
marker of schizophrenia-associated odor[50.82]. These
results were subsequently questioned [50.86], but a fur-
ther study found that schizophrenic patients may indeed
show elevated levels of this compound [50.79]. More
recently, analysis of breath volatiles indicates that com-
pounds like carbon disulfide, pentane, and several other
volatiles might be associated with schizophrenia [50.80,
81]. Interestingly, other patients treated with neurolep-
tics did not share the same pattern of volatiles. This
suggests that compounds associated with schizophrenia
are not a by-product of the medical treatment, although
further studies are needed.
There is accumulating evidence showing that some
affective states, such as anxiety, influence axillary body
odor (for review see [50.11]). One may therefore spec-
ulate whether some affective disorders (e.g., major
depression) are alsoassociated with changes in thebody
odor. To our knowledge, there has not yet been a sys-
tematic investigation on this subject.
50.6 Conclusion
Seen from various perspectives, human body odor is
a highly complex biological system. First, it consists
of several sources, such as the axillae, skin, mouth,
feet, anogenital region, and the scalp. Each of these
sources is characterized by sets of dozens or even hun-
dreds of different volatile compounds. Second, most of
the volatile compounds are not directly produced by
the human body, but mainly result either from residen-
tial or pathogenic bacterial metabolic activity. Third,
each human is characterized by an individual odor pro-
file, which is partly due to the genetic influences. This
profile is relatively stable across the life span and con-
tributes to individual olfactory identity and may affect
social interactions. On the other hand, individual body
odor can also be altered by various intrinsic and extrin-
sic factors.
The main aim of this chapter was to review selected
factors contributing to the inter- and intraindividual
variation in body odor. We first focused on differences
in body odor associated with between-individual dif-
ferences in personality and sexual orientation (other
sources of variation include factors, such as genotype
at the major histocompatibility complex (Chap. 49). We
then described within-individual changes in body odor
due to hormonal influences, in which odor seems to
be intimately associated with hormonal fluctuations, al-
though it must be said that most research has focused on
steroid hormones, such as estrogens or testosterone. It
is noteworthy that other humans can perceive hormone-
related changes in body odor and that odor might
therefore provide important social cues, perhaps espe-
cially those relevant to reproduction, such as actual or
potential fertility. Nevertheless, most of the chemicals
responsible for hormone-related effects are currently
not identified and await further investigation.
One of the major influences on body odor quality
is considered to be diet, which contains numerous aro-
matic chemicals of mainly plant origin. As expected,
various volatiles consumed in the diet affect breath and
fecal odor. However, some compounds might also be
emitted from the skin surface, or can influence body
odor indirectly via several possible mechanisms, in-
cluding oxidative metabolism, nutritional status, and
antibacterial action. The effect of diet might also show
an idiosyncratic pattern as a result of the interaction be-
tween digested food and individual genetic make-up.
Unfortunately, these interactions are currently poorly
understood.
Finally, various disorders and diseases are charac-
terized by specific odors which are often used in clinical
diagnostics or may be at least increasingly utilized in
the future as a diagnostic mean. This is pronounced
in the case of inherited metabolic disorders which of-
ten results in the production of unusual volatiles or
their metabolites. Several carcinomas, such as lung or
bladder cancer, are also known to be associated with
changes in produced volatiles, and these can be used in
early screening. More complex odor profiles are asso-
ciated with some infectious diseases. The potential for
using these changes in screening looks likely to increase
in the near future.
Acknowledgments. Jan Havlíˇ
cek is supported by the
Czech Science Foundation grant (GA ˇ
CR 14-02290S)
and Jitka Fialová is supported by Charles University
Grant Agency (grant number 918214).
Individual Variation in Body Odor References 959
Part F | 50
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