Women who are ovulating tend to pay more attention to their appearance, perhaps in a subliminal effort to attract a mate, according to researchers at UCLA and the University of Wisconsin in Eau Claire.
"They tend to put on skirts instead of pants, show more skin and generally dress more fashionably," said study coauthor Martie Haselton, an associate professor of communication studies and psychology at UCLA.
The study, published online Tuesday in the journal Hormones and Behavior, contradicts the conventional wisdom that human females are among the very few primates who show no outward signs of fertility.
"The thing that is so remarkable about this effect is that it is so easily observed," said Haselton's coauthor, Wisconsin psychologist April Bleske-Rechek.
The researchers studied 30 female college students over the course of a month -- without telling them the true nature of the study. Each was photographed when she was fertile, as determined by a urine test, and when she was not.
The 30 sets of photos, with the faces blacked out, were then shown to 42 male and female judges. The judges deemed the fertile photo most attractive 60% of the time, well above chance.
In one extreme example, the student wore loose-fitting jeans and clunky boots in her lowfertility photo and a skirt and cardigan during ovulation.
Another student, more typically, wore the same black yoga pants and a tank top in both photos. But while the tank top was plain white in the nonfertile photo, the one she wore during ovulation was colored, with a slightly lower-cut neckline trimmed in lace. She also wore a fancier necklace during her fertile period.
"It was my impression that the women were just dressing a little bit more fashionably, but not sexier," Haselton said.
In earlier studies, Haselton and her colleagues had shown that young women were more likely to flirt with males other than their mates while they were ovulating and to stray from their routines in ways suggesting that they were mate-shopping.