Unique male sweat has sexual message: Rice experts find female brain reacts in study

January 08, 2009

A woman may not consciously think of a man's sweat during intimate moments. But her brain appears to recognize the scent and the significance of the emotions it conveys right away.

That's the conclusion of a Rice University study that exposed 19 twentysomething women to various scents, including "normal" sweat from males as well as so-called "sexual" sweat -- more on this in a moment.

Although the research doesn't have immediate implications for male-female relationships -- don't put away the cologne just yet, fellas -- it does advance scientists' understanding of how humans communicate chemically.

Everyone pretty well understands how people communicate through talking and facial expressions. But elsewhere in the animal kingdom, chemicals such as pheromones are commonly used to communicate, be it to attract a mate or warn a competitor.

The question Rice psychologist Denise Chen and her colleagues set out to better understand is how people might communicate chemically and, more specifically, how the brain processes chemical signals from other humans.

The experiment they devised involved the collection of sweat from men who wore rayon/polyester pads under their armpits. For normal sweat, they watched 20-minute educational videos and, for sexual sweat, 20-minute erotic videos.

As it happens, humans have a variety of sweat glands. The sweat produced after a long day's work is different from that after a workout, which is different, in turn, from that produced by a roll in the hay.

Chen and her colleagues then devised settings in which female participants were exposed to different sweat "scents" while being monitored by brain-scanning, magnetic resonance imaging equipment. The women didn't know what they were smelling and couldn't differentiate among the various types of sweats.

But their brains could.

"The sexual sweat lit up different regions of their brains," Chen said.

She said the work suggests the brain can recognize an emotional component in sexual sweat, somehow differentiating it from normal sweat.

The research is part of an emerging scientific discipline that aims to determine whether human brains can process pheromones -- chemicals that trigger a natural behavioral response in animals of the same species.

"This is a very hot and controversial area of research," said Dr. Jay Gottfried, an assistant professor of neurology at Northwestern University.

The Chen study, Gottfried said, adds to the scientific debate, because it used natural scents rather than synthetic ones.

The next step, he said, is to determine whether sweat scents trigger behavioral changes in woman, such as making them feel more or less attracted to a man.