A study of young college women showed they frequently wore more fashionable or flashier clothing and jewelery when they were ovulating, as assessed by a panel of men and women looking at their photographs.

"They tend to put on skirts instead of pants, show more skin and generally dress more fashionably," said Martie Haselton, a communication studies and psychology expert at the University of California Los Angeles who led the study.

Writing in the journal Hormones and Behavior, Haselton and colleagues said their findings disproved the conventional wisdom that women are unique among animals in concealing, even from themselves, when they are most fertile.

Some animals release powerful scents when ready to mate, while others display skin color changes, but human ovulation is notoriously difficult to detect. This is attested to by the frequency of unintended pregnancy, as well as test kits marketed to women wishing to become pregnant but unaware of the likeliest time to conceive.

Haselton's team said their study showed the cues are there, even if men and women are not consciously aware of them.

Women usually ovulate on the 15th day of their menstrual cycles, and this day is when they are the most fertile. Ovulation is easily detected using urine tests, and Haselton's team used such a test to check fertility in their study.

They asked 30 university students to come to their lab for a test, without letting them know the nature of the experiment. "We asked them some things about food, for example," Haselton said in a telephone interview.

The women came back several times over the course of a month and were photographed twice -- once in their fertile phase and another time in their least-fertile phase. The faces in the photographs were blacked out.

WHO LOOKS HOT?

The researchers asked 42 men and women, some older than the volunteers, to assess these photographs by asking, "In what photo is the person trying to look more attractive?"

The judges chose the photograph taken during the women's fertile phases 60 percent of the time, Haselton said. "This is well beyond chance. They were pretty consistent," she said.

"One of the things we found pretty interesting is that people sort of have their personal style, almost like their uniform," she added. "The women would show up to the lab wearing something pretty close to what they wore before, but embellished."

For example, one woman wore loose knit leggings and a tank top in both photos. "In her high fertility photograph, she would be wearing a very pretty tank top and she was wearing more jewelery. The difference was quite subtle," Haselton said.

The fertile women did not necessarily dress more provocatively, Haselton noted. "We did see a little bit more skin. It was my impression that the women were just dressing a little bit more fashionably but not sexier."

Haselton also was interested to note what did not happen.

"There's a popular notion that when women approach menstrual onset, they get out their bloated clothes and they pull out their sweats," she said. "But we didn't find that to be the case."

Haselton's team had earlier reported that women were more likely to flirt and look at attractive men when ovulating.