In an unconscious attempt to outdo female rivals, ovulating women buy sexier clothing, according to a new study in the Journal of Consumer Research.

"Not unlike the chimps featured on the Discovery Channel, women become more competitive with other females 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," write authors Kristina M. Durante, Vladas Griskevicius (both University of Minnesota), Sarah E. Hill (Texas Christian University), Carin Perilloux (University of Texas at Austin) and Norman Li (Singapore Management University).

The authors' research provides some of the first evidence of the influence of hormonal factors on consumer behavior. "We found that, when ovulating, women choose sexier fashion products when thinking about other attractive, local—but not distant—women," the authors write. "If you are in New York, a woman who lives in LA isn't going to be seen as competition."

"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," the authors write.

In the study, researchers had ovulating women view a series of photographs of attractive local women and then asked them to choose clothing and accessories to purchase. The majority of participants chose sexier products than those who were shown photos of less attractive local women or women who lived more than 100 miles away. The authors found that women were not conscious of their choices and the researchers did not find the same effect in non-ovulating women.

The study's findings have practical implications for marketers. "For about five to six days each month, normally ovulating women—constituting over a billion consumers—may be especially likely to purchase products and services that enhance physical appearance," the authors conclude.