For approximately one week every month, millions of women change their economic behaviour and become more focused on their social standing relative to other women, researchers said.
According to study by The University of Texas at San Antonio (UTSA) and the University of Minnesota Carlson School of Management, the ovulatory cycle alters women's behaviour by subconsciously motivating them to outdo other women.
This research could have important implications for marketers, consumers and researchers.
The researchers conducted three studies, one of which had ovulating and non-ovulating women play the "dictator game."
In this popular economic experiment, a person is given a fixed amount of money that she can choose to share with another person.
"We found that ovulating women were much less willing to share when the other person was another woman. They became meaner to other women," said Kristina Durante, lead author of the study.
Whereas non-ovulating women shared about 50 per cent of the money with another woman, ovulating women shared only half as much, keeping the rest of the cash for themselves.
In another study, women made product choices that could either maximise their individual gains or maximise their relative gains compared to other women.
For example, women indicated if they preferred to have a USD 25,000 car while other women got USD 40,000 cars (Option A) or have a USD 20,000 car while other women got USD 12,000 cars (Option B).
The study found that ovulating women preferred Option B, choosing products that would give them higher standing compared to other women.
"What's interesting about this finding is that ovulating women are so concerned about their relative position that they are willing to take less for themselves just so that they could outdo other women," said study co-author Vladas Griskevicius.
But, the studies find that ovulation doesn't always make women want more status. When women played against a man rather than a woman in the dictator game, the researchers found an even more surprising result.
Whereas ovulating women became meaner to women, they became nicer to men. While non-ovulating women shared about 45 per cent of the money with a man, ovulating women gave 60 per cent of the money to the man.
"These findings are unlike anything we have ever seen in the dictator game. You just don't see people giving away more than half of their money," said Durante.
The study was published in the Journal of Marketing Research.