Male
pheromones and sexual attraction
Frances
Thorne 1, Nick Neave 1, Andrew Scholey
1, Mark Moss 1 & Bernhard Fink 2
1.
Human Cognitive Neuroscience Unit, Division of Psychology,
Northumbria University, Newcastle upon Tyne, UNITED KINGDOM.
2. Ludwig-Boltzmann-Institute for Urban Ethology, University
of Vienna, Austria.
Key
words:
pheromone; human; sexual attraction; mate preferences;
menstrual cycle; oral contraception
Submitted:
June 8, 2002
Accepted: June 18, 2002
ABSTRACT
Previous
research has revealed that natural and synthetic pheromones
can enhance ratings of opposite sex attractiveness. The present
study investigated the effects of exposure to male axillary
secretions on female ratings of the sexual attractiveness
of male stimuli. Thirty-two female undergraduates, half of
whom were contraceptive pill users, rated male vignette characters
and photographs of male faces on aspects of attractiveness.
On two separate study days, corresponding to different phases
of their menstrual cycle, stimuli were presented while exposed
to male axillary pheromones and under a control condition
(no pheromone). The order of testing was balanced with respect
to pheromone/control condition and menstrual cycle phase.
Pheromone exposure resulted in significantly higher attractiveness
ratings of vignette characters and faces. Use of the contraceptive
pill or menstrual cycle phase had equivocal effects on some
vignette items and neither had any influence on female ratings
of male facial attractiveness. The results of this study suggest
that exposure to natural male axillary pheromones can significantly
enhance female perceptions of various aspects of male attractiveness.
Introduction
Pheromones are biologically-active substances released by an
individual, and received by another individual of the same species,
in whom they activate specific physiological or behavioural
responses [1]. Pheromones are therefore referred to as ecto-hormones:
chemical messengers that are transported outside the body that
have the potential to evoke certain responses in a conspecific.
The physiological and behavioural effects of pheromones have
been well documented in many invertebrate and vertebrate species
(for reviews see [2, 3]) though their putative effects on human
behaviour and physiology remain equivocal. Scepticism concerning
the existence of human pheromones was due in no small part to
the lack of clear evidence for the existence of a fully functioning
vomeronasal organ (VNO). In many animal species this system
has been shown to detect pheromones and transmit this information
to limbic structures via the vomeronasal-terminalis nerves (for
review see [4]). However, it has since been reported that humans
do possess a functional VNO that responds to pheromones –
even in picogram amounts – in a sex-specific manner, and
produces specific physiological changes [5, 6, 7]. Recently,
the identification of a pheromone receptor gene expressed in
human olfactory mucosa has further strengthened the case for
a functioning VNO [8].
The main producers of human pheromones are the apocrine glands
of the skin located in the axillae of the armpits and pubic
region. The high concentration of apocrine glands found in the
armpits, led to the term ‘axillary organ', which is considered
an independent ‘organ' of human odour production. Apocrine
glands develop in the embryo, but become functional only with
the onset of puberty. At sexual maturation, they produce steroidal
secretions derived from 16-androstenes (androstenone and androstenol)
via testosterone, and as such, the concentrations of several
16-androstenes is significantly higher in males [9]. The action
of aerobic bacteria further serves to metabolise the more odorous
androstenone and androstenol [10]. The 16-androstenes have been
confirmed as male sexual pheromones in pigs [11] and several
authors have speculated that such substances may act as human
male pheromones subserving sociosexual behaviours [12, 13].
In support, several studies have shown that when exposed to
androstenol (often described as a pleasant ‘sandlewood'
smell when detected), female ratings of male attractiveness
are enhanced higher [14, 15, 16]. Filsinger, Braun, and Monte
[17] showed that men under the influence of androstenone rated
photos of males positively, if they liked the scent of androstenone.
However, other authors have reported that exposure to androstenone
(often described as ‘urine-like' or ‘musky') induces
negative perceptions of males [18].
Grammer [12] has argued that there are two different olfactory
signals – androstenol, which induces female attraction
to males, and androstenone, which induces negative responses
in females. Further, though pheromonal communication typically
occurs without conscious awareness, pheromones, when produced
in high concentrations, may still have both conscious and aversive
effects on others. This is further complicated by the fact that
female olfactory sensitivity is moderated by the menstrual cycle,
with smell sensitivity peaking at ovulation [19, 20]. Benton
[20] reported that androstenol application influenced ratings
of subjective mood at ovulation, and Grammer [12] found that
females rated androstenone differently at various phases of
their menstrual cycle. Thus, it has been suggested that human
body odour influences female mate choice in terms of evolutionary
principles. Women seem to prefer the odours of immunocompatible
men [21] and, during their fertile period, judge the body odours
of men with symmetrical bodies (indicative of genetic quality)
as more pleasant [22] which is indicative of genetic quality.
A further complication when evaluating the results from such
studies is that the use of oral contraception may affect smell
sensitivity and gonadal hormone levels [23] thereby possibly
disrupting pheromone detection. Use of the contraceptive pill
does indeed appear to influence female perception of androstenone
[12].
The present study aimed to determine whether naturally occurring
pheromones might act as sexual attractants in humans. Young
female participants, half-using oral contraception, and half
not, were unknowingly exposed to pure male axillary secretions
(unaffected by coryeform bacteria and therefore not consciously
odorous) during two phases of their menstrual cycle. On four
separate occasions (pheromone present and pheromone absent at
two different times of the menstrual cycle) females rated male
attractiveness using vignette characters and photographs.
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