Woman's armpits may hold key fertility clues

Milwaukee Journal Sentinel

(KRT)

MILWAUKEE - A woman's most intimate secrets may not be confined to the pages of her diary, but found in smells emanating from her armpits.

New research from scientists at Charles University in the Czech Republic indicates that a woman's menstrual cycle can be gleaned from scents emitted from her underarms.

Men exposed to these scents prefer the aroma given off during ovulation, when she is most fertile, to those issued during menstruation, when she is less likely to conceive.

The data lend support to the idea that people are not so different from their mammalian - and particularly primate - counterparts, which advertise their fertility by smell, behavior and physique.

And it suggests that women do not have "concealed ovulation" as many researchers have claimed, but, instead a form of "non-advertised" ovulation.

"We're definitely in the money here," said Randy Thornhill, a University of New Mexico biologist who was not involved in the study but has spent the past decade researching the physiological cues of women's fertility cycles.

Although he said the results of the study did not come as a surprise to him, nor will it to other anthropologists and most human biologists, "these kinds of things are going to surprise the reproductive biology establishment," which has long countered the idea that men and women could detect subtle cues about fertility.

The research appears in the January edition of the journal Ethology.

Primatologists have long noted the overt advertising of fertility among monkeys and apes.

The backsides of some, such as the chimpanzee, swell and darken as they become more fertile.

Other primates get their "I'm fertile" point across with behavioral maneuverings - presenting their rear ends to interested males for a little olfactory inspection.

But women - unlike other primates - don't seem to display any overt signs of their fertility. And often seem unable to recognize the signs themselves.

Several theories have been posited concerning this concealment.

Some have suggested it may reduce competition between males, allowing for greater cooperation; a necessity for the survival of small bands of hunter-gatherers, as our ancestors surely were.

Others think the lack of display may promote fatherly care by confusing paternity - making every male who's had contact with that woman suspect the child could be his own, thereby reducing the risk of infanticide.

And because ovulation is often concealed from women themselves, one researcher proposed there must be a benefit in not knowing.

Indeed, it was argued that if a woman knew when she was fertile, she might avoid sex during her most fertile period so as to avoid the pain and possibly life-threatening prospect of delivering a child.

Despite the large number of theories, there are few experimental studies addressing the question of concealed ovulation.

As the Czech authors point out in their study, none of these evolutionary theories accounts for olfactory signals; they focus exclusively on visual cues for fertility.

This, say the authors, doesn't make sense because hormones, which cause ovulation, are probably more closely linked to body odors than bodily appearance. Therefore, they argue, one should expect "body odor attractiveness to be a potential cue to female fertility status."

Other scientists have explored this area of research, and their results have been contradictory.

These studies have principally relied on men who are asked to smell T-shirts women have worn during their cycles.

In some of these studies, there seemed to be a correlation between attractiveness and a woman's fertility, based on a score given by the sniffing men. In others, there was no indication the two were tied.

The Czech researchers claim these studies were faulty for several reasons. But the chief fault, they say, resides in the use of T-shirts as smell receptacles because these cotton undergarments could be picking up extraneous smells not related to the changes in a woman's cycle.

Thornhill, the New Mexico biologist, said another problem was the manner in which men were introduced to the shirts. When men were asked to rate the scents between different women, the studies lost their power. But if men were asked to rate T-shirts from just one woman, with shirts representing different periods during her cycle, the results showed a correlation.

"Sampling between women can confound the results," he said, because every woman smells different.

Factors such as diet, health and genetics can make one woman smell more pleasant than another, regardless of her cycle phase.

Instead of relying on shirts, the Czech researchers asked 19 women to wear adhesive cotton pads under their arms.

They wore the pads for 24 hours and were asked to refrain from using perfumes, deodorants, antiperspirants; from applying shower gel or aftershave; from eating foods containing garlic, onion, chili, pepper, vinegar, blue cheese, cabbage, radish, fermented milk products and marinated fish.

They were also asked to abstain from alcohol and other recreational drugs; to avoid smoking and to refrain from sexual activity - even sleeping in the same bed as their partner on the day before wearing the pad and during the day that they word the pad.

The women wore the pads once every seven days. And once the 24 hours were up, they put the pad in an opaque jar that they immediately returned to the researchers, who had men lined up at the lab to start smelling.

Only 12 women made it through to the end of the study - and it was from their scents that a select group of men judged their smell.

The smells were rated for their intensity, pleasantness, sexual attractiveness and femininity. The study was designed so that all men rated odors collected from the same women.

The results indicated that men found the scents the most pleasant and attractive during the women's follicular phase, or when they were most likely to conceive. And they found the smells least attractive during the menstrual period.

But whether these subtle smells make any difference in today's world of perfumed soaps and deodorants is another question, one that Jan Havlicek, lead author of the study, said needs to be investigated.

"It should be said that perfumes interact with our natural body odor, and that menstrual cycle changes can possibly be perceivable," with or without the influence of scented personal care products, he said. "Moreover, boyfriends and husbands also experience their partners without perfumes."

Men exposed to these scents prefer the aroma given off during ovulation, when she is most fertile, to those issued during menstruation, when she is less likely to conceive.

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(c) 2006, Milwaukee Journal Sentinel. Distributed by Knight Ridder/Tribune News Service.