A new study by University of California Berkeley shows a pheromone found in male sweat and perfumes can raise levels of the hormone cortisol in women.
The study, published in this week's The Journal of Neuroscience, provides the first direct evidence that humans, like rats and some insects, secrete a scent that affects the physiology of the opposite sex.
Similar phenomena have been suggested but not proved before: Studies such as Elizabeth McClintock's work in the early 1970s -- in which women living together in a dormitory were found to have synchronous menstrual cycles -- indicate that a sort of sixth sense exists that allows people's bodies to communicate with one another.
"Many people argue that human pheromones don't exist, because humans don't exhibit stereotyped behavior," said Claire Wyart, a postdoctoral researcher in the Berkeley Olfactory Research Program, leader of the study. "Nonetheless, this male chemical signal, androstadienone, does cause hormonal as well as physiological and psychological changes in women."
The study was inspired by previous studies by Wyart's colleague Noam Sobel. Sobel found that the chemical androstadienone -- a compound found in male sweat and an additive in perfumes and colognes -- changed mood, sexual arousal, physiological arousal and brain activation in women.
Wyart's research exposed 21 subjects to 30 milligrams of androstadienone and to yeast, which is not in sweat but has a similar olfactory sensation. The participants took 20 sniffs of each in two separate trials. The researchers measured physiological vital signs like body temperature, skin conductance, ear pulse, blood pressure, respiratory function and cardiac rate throughout the experiment. They also measured mood and sexual arousal by checking the levels of cortisol, a hormone that has been associated with arousal and mood, in saliva samples.
Compared to their response when sniffing a control odor (yeast), the women who sniffed androstadienone reported an improved mood and significantly higher sexual arousal, while their physiological response, including blood pressure, heart rate and breathing, also increased.
In addition, however, the study found that cortisol levels rose within about 15 minutes of sniffing androstadienone, and remained elevated for more than an hour.
Wyart noted that the question remains: Which comes first -- the change in cortisol level, which may induce a change in mood or arousal; or a mood change that increases cortisol levels?
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