Scientists from the University of California, Berkeley, say that just a whiff of a chemical found in male sweat is enough to raise levels of the hormone cortisol in heterosexual women.
Study leader, Claire Wyart, said the new study, published in The Journal of Neuroscience, built on previous work that found that the chemical androstadienone - a compound found in male sweat - changed mood, sexual arousal, physiological arousal and brain activation in women.
But why androstadienone should have these effects is something of a mystery, as humans lack the appropriate organs in the nose to be able to sense pheromones as animals and insects do. "Pheromones are chemical molecules expressed by a species aimed at other members of the species to induce stereotyped behavior or hormonal changes," Wyart explained. "Many people argue that human pheromones don't exist, because humans don't exhibit stereotyped behavior. Nonetheless, this male chemical signal, androstadienone, does cause hormonal as well as physiological and psychological changes in women."
In the past, male underarm sweat has been shown to improve women's moods and affect ovulation, so the researchers set out to test whether androstadienone affects hormone levels as well, focusing on the hormone cortisol (cortisol is secreted by the body in times of stress, preparing it for "fight or flight").
In the experiment, female subjects were asked to take sniffs from a bottle containing androstadienone. Cortisol levels were then measured from saliva samples and the researchers found that those levels rose within about 15 minutes of sniffing androstadienone, and remained elevated for more than an hour. Additionally, 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.
But things aren't clear cut, says Wyart, as the question remains: Which comes first - the change in cortisol level, which induces a change in mood or arousal; or a mood change that increases cortisol levels? "We next need to look at other hormones that could explain the diversity of effects of androstadienone on sexual arousal and mood," she concluded.
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Source: University of California, Berkeley