A research study from the University of Minnesota’s Carlson School of Management has found that ovulating women unconsciously buy sexier clothes.

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.