Pheromones, which have been known to influence sexual activity, aggression, and territory marking, have been found in many animals, including amoebas, fish, hamsters, and monkeys (3). However, whether or not these chemicals affect, or even exist in humans, has been a subject for debate in the scientific community. Since pheromones are not detectable by the human sense of smell, scientists believe that pheromones are sensed by the vomeronasal organ (VNO), part of the olfactory system and located inside the mouth or nose (9). For many years, the existence of the VNO produced much speculation because it had only been found occasionally in adult humans, and when it was found, it was believed to be vestigial. However, in 1985 a study was conducted in which the noses of 100 human adults were examined post-mortem. The VNO was found in the septums of 70% of those examined. Since 1985, much evidence has been gathered to suggest the presence of the VNO in most adult humans (2), but many scientists still believe it to be a functionless organ that was inherited from some ancestor of humans. However, recent genetic research has shown the possibility of a receptor in the nose that could sense pheromones. When searching the human genome for genes that had similar sequences to those of rodent pheromone receptors, scientists found one gene that could produce a pheromone receptor, and when searching olfactory tissue from the human nose, they found this receptor (5).
In the past few years researchers have believed to have found scientific proof that "humans have the potential to communicate pheromonally, either by using an unidentified part of the main olfactory system, or perhaps with a sixth sense, with its own unique pathway (1)." One study was based on the observation that women living together develop synchrony of menstrual cycles. In this study, researchers placed gauze pads under the armpits (a body part where pheromones are believed to be secreted in the sweat) of nine women during specific phases of their menstrual cycle. They each wore the pads for at least eight hours. After being treated with alcohol and frozen, the pads were placed under the noses of twenty other women. The women that sniffed the pads of the women that had been in the preovulatory phase of their cycle found that their own menstrual cycles were shortened from one to fourteen days. The women that sniffed the pads of the women that had been in the ovulation phase if their menstrual cycles found that their own cycles were lengthened from one to twelve days (1). This suggests that there are substances or chemicals released from women that can accelerate or delay menstrual cycles (4), which influence the release of eggs (10), and thus lead to synchrony of cycles of women living in proximity. However, since the substances from the pads were placed on the upper lip, it is difficult to say how these women sensed them, "whether it's through skin, the mucous membranes in the nose, or the VNO (9)."
Another study shows that babies prefer clothing worn by their own mothers. In this study, ten mothers were asked to wear a cotton pad in their bras for three hours. The pads were then given to their babies to see whether or not they could distinguish between the pads worn by their mothers and those worn by strangers. At the age of six weeks, eight babies had responded by sucking to their mother's pad, one responded to a stranger's pad, and one did not react to its mothers pad, but reacted with a cry to a stranger's pad (3). Researchers believe this could suggest that men and women choose their mates by sniffing out those that have "compatible immune systems (9)."
Some researchers believe that there is a relationship between physical attractiveness and body odor. In a study to test this hypothesis, 16 males and 19 females were asked to wear a t-shirt on three consecutive nights without using any perfumes or deodorants. Fifteen more subjects each smelled a t-shirt of the opposite sex, rating its scent on pleasantness and sexiness. Another group of 22 men and women were asked to rate the subjects that wore the t-shirts in terms of physical attractiveness. The results showed a correlation between facial attractiveness and sexiness of body odor of females. However, there was only a correlation between facial attractiveness and sexiness of body odor of males when females raters were in "their most fertile phase of menstrual cycle (day 5 to 16) (6)." Nevertheless, this study does suggest a relationship between physical attractiveness and attractiveness of body odor.
A similar study attempted to find out whether or not males can sense ovulation by smelling copulins, fatty acids in vaginal secretions. Males smelled copulin samples from women who were in three different phases of the menstrual cycle. The results showed that males generally could not distinguish between a pre-menstrual, menstrual, and ovulatory scents. However, the males also rated the physical attractiveness of the females, and results showed that females were rated more attractive when the males were smelling their copulins then when they were weren't, and that their testosterone levels increased when they were smelling the copulins (7).
This research strongly suggests the presence of chemicals that cause changes in non-conscious behavior. In my research, I mostly found information that discussed scents that females produce that attract males or offspring, such as copulins, or chemicals that affect the menstrual cycle. This is interesting because it supports the old stereotype that in nature males search out females as mates and not vice versa. The existence of the VNO in females might suggest otherwise, but it should be a topic for greater research. I was also a bit wary of the studies that involved the rating of physical attractiveness, simply because attractiveness is so relative. In any case, my research suggests that sexual receptivity is based on more than attractiveness of physical features.
3) Pheromones in Humans: Myth or Reality
5) Academic Press Daily InScight
6)Ludwig-Boltzmann-Institute for Urban Etholo
7) Ludwig-Boltzmann-Institute for Urban Ethology
8) Ludwig-Boltzmann-Institute for Urban Ethology
9) Sniffing Out Human Pheromones