ShareThisSure, love stinks. But it may yet be ill-advised for a guy to present his beloved a sweaty T-shirt in lieu of flowers, perfume or a card on Valentine's Day.
It's been 50 years since scientists first discovered pheromones -- chemical secretions that trigger mating and other social behaviors in creatures from moths to mice. But there's still no solid evidence that humans use such signals to find a mate.
Then again, there is considerable research that suggests that people do get sexual signals from subliminal scents, although scientists continue to debate just what they are and how they work.
And because people are endlessly fascinated with what attracts us to each other -- and just as inclined to seek an edge in love as in war -- both writers and fragrance marketers have kept the notion of pheromones before the public.
"Sure, the claims are out there: 'All you have to do is put this on and you'll score.' But there's nothing in the published biomedical literature that we have any kind of pheromone that draws a partner," said Charles Wysocki, a neuroscientist at the Monell Chemical Senses Center in Philadelphia who studies the effects of odors on biological response.
Although humans' sense of smell may not be as sharp as it was back when we were living in caves and constantly on alert for predators and prey, scientists calculate that the average human nose and brain can still pick up more than 10,000 odors, not all consciously.
Since we are more complex animals, the natural scents of other people seem to have both direct and subtle effects on our bodies and moods.
"There are a lot of factors in play that determine if we go running off madly together," Wysocki said.
Martha McClintock, a University of Chicago psychologist, pioneered research 30 years ago that found women living together in a college dorm gradually synchronized their menstrual cycles. And further research showed that simply putting sweat samples from women on the upper lips of other women for some days or weeks would have the same result as living together.
Other studies have shown that women living in close proximity to men have more regular menstrual cycles, and that girls living in a home with an adult male experience puberty some months later that those where there is no father figure.
In 2007, researchers at the University of California-Berkeley reported that a few whiffs of a male-sweat pheromone called androstadienone raised levels of the hormone cortisol in women.
Cortisol is generally associated with stress, but also plays a role in arousal and brain activation.
The experiment involved 48 women, with half being asked to sniff bottles containing androstadienone, the others, a somewhat similar-smelling yeast solution. Cortisol levels in the women exposed to the sweat rose within the first 15 minutes of exposure, and stayed elevated for more than an hour. And that group reported improved mood and sexual arousal, along with changes in blood pressure and heart rate.
The researchers noted none of this proves that any of the women would have swooned over a sweaty male, but does show the male chemical signal can produce hormonal, physical and psychological changes in women.
Several studies suggest that there is a genetic signal behind women's response to male sweat. Swiss researchers have found in a T-shirt test that women preferred the odor of men who were most genetically dissimilar to them, an evolutionary advantage in a mate when seeking diversity and healthier children.
Thus, some women may find a guy's natural smell alluring, and vice versa, while others may be indifferent to the odor, or find it disgusting.
Other recent studies indicate that men's sweat carries a signal for genetic fitness, at least as far as having facial and body symmetry -- features and body that are balanced and well-proportioned.
Specifically, when women are in the fertile time of the menstrual cycle, they have a preference for the smell of men who are symmetrical over those with less-balanced bods.
One experiment found that fertile women who viewed photos of men found the same symmetrical men attractive, as did a group that rated candidates only by smell.
On the Net: http://www.monell.org
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(Reach Lee Bowman at bowmanl(at)shns.com.)
THE MEDICAL JOURNAL
