Emerging research has begun to uncover how human bodies communicate with each other through scent, which may be a key to understanding sexual attraction in men and women.
In a recent study, Claire Wyart, a postdoctoral neuroscience researcher at UC Berkeley, discovered that a molecule, androstadienone, which is highly present in human male sweat, causes an elevation in mood and sexual arousal in women.
In Wyart’s study, this elevation was indexed by measuring vital signs such as body temperature, pulse, blood pressure and the levels of cortisol, a hormone associated with mood and arousal.
Wyart’s team found that by simply smelling the androstadienone, positive mood, alertness, arousal and cortisol levels increased in female subjects and continued to increase with prolonged exposure.
The study is the first to provide direct evidence that humans, like animals such as rats and moths, secrete a scent that causes a physiological reaction in the opposite sex.
“This is the first time we have found that hormonal level can be changed in women just by smelling the components of male sweat,” Wyart said.
Future research will also look at the effect of smelling components of women’s sweat on men, Wyart said.
“I am guessing that there are some estrogen scents that cause similar reactions in men as well,” she said.
Recent research has shown that men are also affected by the scents that women emit. The body scent of women may relay subtle cues of ovulation to men, said psychology and communication studies Professor Martie Haselton.
Men may subconsciously sense when women are most fertile, and they become more attracted to women during those days of their cycle, Haselton said.
In another study, T-shirts were given to female subjects and worn during the different stages of their cycles and then brought back to the research lab and given to male participants to smell, Haselton said.
“The T-shirts were rated as more attractive when worn for several high-fertility days of the cycle than when they were worn for several low-fertility days of the cycle,” said Haselton.
In this way, men may detect on some level the days when women are most fertile and adjust their sexual behavior accordingly, Haselton added.
New research is also showing that via the sense of smell, people may be attracted to individuals who have certain genes that are dissimilar to their own.
The major histocompatibility complex is a set of genes involved in the immune system and is detected on a certain level through body scent, Haselton said.
Early research on the effect of the MHC gene selection on mate choice was done in mice, said Greg Grether, a biology professor who conducts research on sexual selection in several different species of animals in his lab at UCLA.
“Mice prefer to mate with individual types that are different from their own MHC type,” Grether said.
By mating with individuals of different MHC types and therefore acquiring more diverse MHC genes, the mice may increase the immunological competence, or strength, of their offspring, allowing them to be more resistant to different types of diseases, Grether said.
This trend, Grether said, can also be seen in humans.
“People find others with MHC genes different from their own more attractive,” Haselton said.
Another study showed that women who shared similar MHC genes with their partners were less sexually attracted to their partners and were more likely to have had affairs during the course of the relationship with those partners, Haselton said.
The research on MHC is consistent with what is known as the “good genes” hypothesis.
“It is the idea that females, by being choosey, obtain better genes for their offspring,” Grether said.
In the “good genes” hypothesis, it is thought that by carefully choosing their mates, women can gain access to genetic benefits that are passed from parent to offspring that could enhance the survival and mating success of that offspring, Haselton said.
In the case of MHC genes, by using their sense of smell, individuals seek compatible genes, or genes that combine well with the mate chooser.
“There is good evidence that choosing a mate with a particular set of genes that are different from your own is beneficial to offspring,” Haselton said.