No point hiding it. Men can smell women's fertile phase.

A Good Nose for Ovulation

A long-held belief among anthropologists is that there's no way to tell exactly when a human female is ovulating. Men hoping to catch her fertile phase, therefore, would have no option but to hang around--and not go gallivanting. But a study in the July issue of Behavioral Ecology shows that the male brain isn't totally clueless. As it turns out, men find a woman's body odor most sexy when she's ovulating.

Unlike most female primates, with their swollen buttocks and other not-too-subtle signals, women do not advertise their fertile periods. Or so one theory goes. But studies on human odor in the 1990s turned up telltale signs that men may have subtle ways of gauging their partners' reproductive state. To test whether men can also choose the most fertile scents from a set of unknown women, a group of researchers conceived a study using smelly T-shirts.

Seppo Kuukasjärvi of the University of Jyväskylä in Finland and his colleagues asked 81 female students for details of their menstrual cycles and also whether they were taking contraceptive pills. Then they gave the women T-shirts to wear for two consecutive nights, after which the garments were tested by 43 volunteer sniffers of both genders. Male sniffers rated the scents of women in mid-cycle, around the time of ovulation, as most attractive, whereas the female sniffers did not. All sniffers were clueless about the menstrual cycle of pill-using women, though. Because the pill suppresses ovulation by blocking the production of certain hormones that peak at mid-cycle, the sexy smell is probably derived from these hormones, says evolutionary biologist Esa Koskela, one of the paper's authors.

Anthropologist Craig Palmer, who studies the evolution of human sexual behavior at the University of Missouri in Columbia, is pleased with the new contribution to the field. But he adds that there's probably a lot more to the story than simply what men smell. For example, he says, women may feel jealous when they smell other women in ovulation.

Related site
University of Vienna's site on human pheromones