Women are more likely to select clingy clothes when they are ovulating, a study has found.
But the University of Minnesota study of 100 women found these hormonal shopping habits were triggered by the proximity of attractive women.
The researchers suggest in selecting tighter clothes, the women were trying to stand out from love rivals.
The Journal of Consumer Research study said there should be more analysis of how hormones affected shopping habits.
Women at different stages of their menstrual cycle were shown images of attractive women living locally or far away.
They were then asked to choose clothes and accessories which they would like to buy.
Women who were ovulating and who had seen photos of attractive local women were most likely to buy "sexier" clothes compared with those shown photographs of unattractive local women or women who lived more than 1,000 miles (1,600km) away.
Dr Kristina Durante, who led the research, said: "The desire for women at peak fertility to unconsciously choose products that enhance appearance is driven by a desire to outdo attractive rival women.
"If you look more desirable than your competition, you are more likely to stand out."
The team said even though the end result was about attracting the best romantic partner available, ovulating women's choice of dress was 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," she said.
And she said the study's findings could influence how and when products were marketed to women.
"Our findings suggest marketers for many types of female products are well served to strategically time their mailings, coupons, electronic solicitations, and direct requests to the specific window when women are ovulating."
Dr George Fieldman, a London-based psychotherapist, said the findings were interesting.
"What this study in part reveals is that people are only semi-conscious of the underlying reasons behind the choices they make in the context of buying sexy clothes," he said.
"Women do the choosing [of mates] but in order to enable them to choose, they need a good number of suitors to select from."