Ovulating women unconsciously buy sexier clothes, says new research from the University of Minnesota's Carlson School of Management. The study finds that ovulating women unconsciously dress to impress -- doing so not to impress men, but to outdo rival women during the handful of days each month when they are ovulating.

"The desire for women at peak fertility to unconsciously choose products that enhance appearance is driven by a desire to outdo attractive rival women," says Kristina Durante, a post-doctoral fellow at the Carlson School. "If you look more desirable than your competition, you are more likely to stand out."

This research, forthcoming in the Journal of Consumer Research, provides some of the first evidence of how, why, and when consumer behavior is influenced by hormonal factors. Durante and co-authors focused their predictions on the fact that competition for a suitable partner would be influenced by a woman's fertility status.

"We found that, when ovulating, women chose sexier fashion products when thinking about other attractive, local but not distant women," says Durante. "If you are in New York, a woman who lives in LA isn't going to be seen as competition."

Although the end result is to attract the best romantic partner available, Durante's research found that ovulating women's choice of dress is motivated by the other women in their environment. "In order to entice a desirable mate, a woman needs to assess the attractiveness of other women in her local environment to determine how eye-catching she needs to be to snare a good man," Durante says.

In the study, researchers had ovulating women view a series of photographs of attractive local women and then asked them to choose clothing and accessory items to purchase. The majority of participants chose sexier products than those who had been shown photographs of unattractive local women or women who lived over 1000 miles away. This change in consumer choice is not a conscious decision and non-ovulating women are not subject to the effect.

The current findings have practical implications for marketers because ovulatory cycle effects may profoundly influence women's consumer behavior. "For about five to six days every month, normally ovulating women -- constituting over a billion consumers -- may be especially likely to purchase products and services that enhance physical appearance," says Durante. Such products include not only clothing, shoes, and fashion accessories, but also cosmetics, health supplements, fitness products, medical procedures, and more.