Introduction
The word "pheromone" is a combination of the Greek
words Pheran, which means "to transfer," and Horman, which means
"to excite." Pheromones are chemical agents secreted by humans,
insects, and animals in order to bring about specific responses or effect the
activation of particular behavioral manifestations or hormonal changes in
members of the same or opposite sex of the same species. These signaling
chemicals may appear in several body fluids, such as urine, perspiration, the
product of special exocrine glands, or genital mucous.
Pheromones are usually categorized into two primary classes:
releaser pheromones: these have immediate behavioral
responses and include attractants and repellents;
Primer pheromones, which underlie longer-lasting changes in
behaviour or development via the activation of the
hypothalamic-pituitary-adrenal axis. With this, pheromones could be further
divided into various types, including aggregation pheromones, alarm pheromones,
epideictic pheromones, territorial pheromones, trail pheromones, information
pheromones, and sex pheromones.
What are pheromones?
Officially discovered in 1959 Trusted Source, pheromones are
various chemical substances that are secreted through fluids like urine and
sweat outside of the body.
Basically, pheromones are a form of silent communication.
They carry messages from one individual to another of the
same species. It sparks a response in the person receiving those messages,
whether it is a hormonal response or an acting out of some sort behaviorally.
Smell and pheromones
The sense of smell is crucial as an arousal system-one
calling attention to significant environmental events and changes. Odour
memories can be stored in humans, consequential to odour preferences or
aversions. Olfactory signals were shown to induce emotional responses even if
an olfactory stimulus is not consciously perceived, presumably because
olfactory receptors not only send projections to the neocortex for conscious
processing but also to the limbic system for emotional processing.
The traditional view on pheromone-sensing assumed that most
mammals had two parallel olfactory systems with distinct functional roles: one
principal olfactory system recognizing conventional odorant molecules, and one
vomeronasal system, dedicated specifically to pheromone detection. In humans,
although the vomeronasal organ itself was considered vestigial, its function
had been assumed by various different researchers to make use of a distinct
sensory passage in order to detect pheromones. Nasal receptors near the
entrance of the nose were reported to react strongly to air containing
pheromones, transferring its stimulation to the hypothalamus with a signal of
attraction, sexual desire, arousal, and so forth.
Jahnke and Merker
described the ultrastructure of the adult human VNO as having a
duct-like invagination of the epithelium surrounded by numerous exocrine glands
with short ducts. Lying deeper are pseudostratified columnar epithelial cells
with plump processes, kinocilia, and microvilli at the apical cell membrane.
Under the basement membrane, numerous myelinated and unmyelinated axons are
present in the vascular lamina propria.
Steroid hormones, as chemical sex signals in humans, may
excite an electrical response from the residual VNO to affect hormone levels,
as evidenced by Monti-Bloch and Grosser. According to Wood, "the
effectiveness of a chemosensory input to particular brain nuclei depends
critically on the simultaneous presence of a steroid hormone in the same
nucleus.".
Foltán and Sedý
supposed that a traumatized VNO due to Le Fort I osteotomy of the
maxilla may influence the patient's social life concerning the selection of a
mate and sexual relations. Keller et al.
demonstrated that both the main and accessory olfactory systems are
capable of processing partially overlapping sets of sexual chemosignals in a
complimentary way to support aspects of controlling sexual behaviour. Savic et
al. added that anosmics cannot stimulate
the hypothalamus with oestra.
Are there different types of pheromones?
Pheromones are currently classified into four main
categories:
- Releasers: These pheromones trigger an immediate and specific behavioral response, such as attraction to a potential mate.
- Signalers: Social in nature, signaler pheromones communicate information about an animal, including its health, recent diet, and social status.
- Modulators: These pheromones subtly affect mood and emotions.
- Primers: Primer pheromones influence reproductive and developmental processes, such as puberty and menstruation.
How Do Pheromones Work?
Mammals detect pheromones through their olfactory system
deep inside the nose, which also plays an important role in smelling and
tasting food. Chemical signals enter the nose in the form of gas or liquid and
are detected by two organs, the vomeronasal organ-VNO, popularly known as
Jacobson's organ-and the main olfactory epithelium (MOE). These organs send
signals to the brain for processing.
How Do Pheromones Work in Humans?
Isolated by scientists in the 1950's, pheromones are
generally accepted as those chemicals released that signal another animal of
the same species. These signals fire specific behaviors necessary to survive
and reproduce, such as mating.
Overview of Studies
In as much as pheromone attraction has been evidenced on several mammals, no verifiable conclusion could be drawn if the very phenomenon actually applies to humans.
Key findings include:
Animal Studies: Experiments carried out in mice reveal that
the presence of male-specific pheromones, in fact serves to activate sexual
arousal among females. These experiments suggest that pheromone response is
learned and remembered for future interactions. The evidence till now suggests
that the expert speculation on corresponding sexual and reproductive responses
in human may exist though research in this aspect is scanty.
Menstrual Synchronization: Among many conclusions, one had
indicated that human sweat has the potential for synchronizing the menstrual
cycle of ladies
Mother-Infant Recognition: Others had studied the hypothesis
regarding a pheromone-like odors existing in the nipple area, enabling newborns
to recognize their mothers
Regardless of these attractive conclusions, it is not proven
yet that the effects are due to a specific pheromone.
Pheromones and sexual preference
There are conflicting theories on the human body odor aspect in partner selection and sexual preference.
Oliva postulated that homosexuality may be biologically tied to an intact vomeronasal organ that would enable it to detect same-sex pheromones.
- Martins et al. tested the hypothesis that body odor may influence partner choice. Heterosexual and homosexual men and women were asked to select between body odors of heterosexual and homosexual men and women. Results showed that gender and sexual orientation each contributed to variation in preferences for body odor.
- Savic et al. examined the brain's response to two pheromones, AND and EST, across homosexual men, heterosexual men, and heterosexual women. They found that, like heterosexual women, homosexual men exhibited hypothalamic activation to AND, but heterosexual men did not. Common odors, in contrast, were similarly processed across groups, indicating a link between sexual orientation and hypothalamic activity.
- The same tests were run by Berglund et al. with lesbians, and it was found that, in contrast to heterosexual women, lesbians processed AND through the olfactory system without activation of the anterior hypothalamus. When exposed to EST, lesbians showed partial hypothalamic activation, somewhat similar to the pattern of response seen in heterosexual men. This would indicate differentiated processing of pheromone-like stimuli according to sexual preferences.
- Sergeant et al. studied women's perception of body odor in front of men with different sexual orientations. Women rated the body odor of homosexual men as more pleasant and attractive than that of heterosexual men. Thus, it may be assumed that sexual orientation affects the production of body odor and olfactory perception.
- Savic and Lindström reported sex-atypical brain asymmetry and functional connections among homosexual individuals, suggesting neurobiological etiology instead of behaviors learned through experience.
- Bodo and Rissman suggested that besides pheromone-induced neural responses, the androgen receptors could also be another reason in sexual differentiation of social preferences.
- Savic et al. showed that smelling androgen-like compounds activated the hypothalamus in women, while men's hypothalamus responded to estrogen-like substances, hence giving a physiological basis for sex-specific behavioral responses.
- Saxton et al. demonstrated that AND was able to affect women's judgments of the attractiveness of men; in other words, men smelled more attractive when women were exposed to AND.
- Lundström et al. surmised that body odor, along with other social stimuli, might stimulate specialized neural networks. Familiar body odors arouse recognition brain areas, while unfamiliar odors provoke areas involved in fear, for example, the amygdala.
Pheromones and sexual functions
The role of pheromones in sexual functioning has been
studied in detail in both sexes, but considerably more is known about animals
compared to humans. For instance, Udry studied sexual frequency, orgasm, and
the menstrual cycle, showing that women experience sexual intercourse
approximately six times more often and have more orgasms during ovulation. On
the other hand, during and immediately after menstruation, the probability of
having sexual intercourse or reaching orgasm is greatly reduced. These
observations, taken in conjunction with the fact that women generally have a
keener sense of smell, suggest a probable pheromonal effect on sexual behavior.
Other researchers, Campieri et al., reported that zinc chloride treatment of
hemodialyzed patients relieved impotence, as well as taste and smell problems.
Is body odour attraction based on our immune system?
Work on subjective rating of body odour has suggested that
humans have preferences for the HLA of dissimilar people. A female mouse would
choose a mate whose MHC genes were least similar to her own ; human females too
prefer men whose MHC genes are the least similar to their own.
The experiment used an unscented T-shirt that men were to
wear for two consecutive nights, without using deodorants or scented soaps.
Three shirts from men who have similar MHC genes and three shirts from men with
dissimilar MHC genes were presented to women. They preferred the scents of men
whose MHC genes were different. Women on birth control pills would often prefer
the T-shirts of men that had similar MHC genes. One hypothesis is that birth
control pills trick the body into thinking its pregnant, and women on the pill
often report that they are attracted to odors reminiscent of home and kin .
Pause et al. showed that pre-attentive processing of body
odours of HLA-similar donors is faster and that late evaluative processing of
these chemo-signals activates more neuronal resources than the processing of
body odours of HLA-dissimilar donors. In same-sex smelling conditions,
HLA-associated brain responses exhibited a different local distribution in male
(frontal) and female (parietal) subjects. They therefore came to the conclusion
that odours of HLA-similar persons serve as significant social warning signals
in inter- and intra-sexual human relations. Such HLA-related chemosignals may
be involved in female and male mate choice and in male competitive behaviour.
The behaviorally relevant signals, if any, provided by the
proposed HLA-related attracting signals would thus seem minimal due to the
extreme polymorphism of the HLA gene loci. So far, the role of the HLA-related
chemo-signals has not been specified in either the same- or opposite-sex
relationships.
Finally, the role of these substances in maintaining a
definite physiological response and in influencing our attitudes and our life
as a whole remains open. In other words, smells and the way we perceive them
are issues that require further time and effort to unfold all the mysteries
thereof. Humans are not systems instinctively falling into a behavioral
response to an odor, but rather thinking beings moved toward a type of behavior
by pheromones in concert with the highest intellect in the animal kingdom.
Indeed, in mammals, olfaction plays a major role in sexual attraction,
excitement, and even in triggering ovulation. However, in humans, because of
the highly developed and complicated brain, it plays a minor role and is
considerably substituted by vision and/or fantasy in men and by hearing and/or
touch in women. Also, while olfaction changes the neuroendocrine balance in
mammals, in humans, olfaction is influenced by hormones themselves.
Conclusion
Naturally occurring substances, pheromones are chemical
messengers of animals that may result in behavioral responses from others of
the same species when these animals release them through sweating. Behavioral
responses may range from sexual attraction, choice of a mate to warning signals
of danger.
For these reasons, even experts disagree whether pheromones
exist in humans because of inadequate scientific evidence to confirm the
existence of human pheromones. Although some research studies found several
steroids, such as androstadienone and estratetraenol, to serve as pheromones in
human sexual responses, their purported pheromonal activities were never
replicated by other studies.
This concept has been utilized in the production of
fragrances, which include pheromones that supposedly enhance attraction.
However, scientific evidence is lacking in those formulations.