New research finds women are more likely to wear red during periods of high fertility.

(Photo: Urban Muser/Flickr)

Ladies: Do you happen to be wearing red today? If so, why did you choose that particular blouse or vest? A whim? Your funky sense of fashion?

In fact, there is a good chance your selection was strongly influenced by your hormones.

As we first reported way back in 2008, men have a biological predisposition to perceive red as a sexual signal, and as such are more likely to take notice of women wearing that color. Subsequent research revealed females have picked up on this fact and—driven by either conscious choice or instinct—often resort to red when attempting to attract a mate.

"These results suggest that women are more likely to exploit men's preference for women wearing red on days when conception is possible."

A just-published study that focuses on hormone levels confirms this dynamic and ties it directly to one's fertility cycle. It finds that, on days when conception is most likely, that blue dress is likely to stay at the back of the closet, passed over for the power of pink.

The research, by a team led by psychologist James Roney of the University of California-Santa Barbara, featured 46 young women (with a mean age of 18.8) who attended weekly lab sessions for the duration of either one or two menstrual cycles. At each visit, they provided saliva samples, which were analyzed for concentrations of the hormones estradiol, progestrone, and testosterone.

The women were photographed in color during each of their visits to the lab. Researchers noted whether their shirt, sweatshirt, dress, or jacket was primarily or entirely of a red hue.

"Across all ovulatory cycles, the participants wore red 17 percent of the time during the fertile window, but only 8 percent of the time on other cycle days," the researchers report in the journal Psychological Science. Put another way, "the odds of wearing a red top were about 2.5 times higher inside the fertile window."

"These results suggest that women are more likely to exploit men's preference for women wearing red on days when conception is possible," Roney and his colleagues conclude. "This complements other findings of women's increased motivation to enhance their attractiveness during the fertile window."

"It is not entirely clear why red in particular is used to enhance attractiveness," the researchers concede. But it's not entirely a mystery, either.

As Andrew Elliot and Daniela Niesta noted in the aforementioned 2008 study, many non-human primates display red on some part of their body when they are nearing ovulation. There is good reason to believe the association between the color and enhanced fertility—which sends a signal that this would be a fine time to reproduce—is shared by humans.

It's all a reminder that however sophisticated we perceive ourselves to be, including in the realm of fashion, our choices are driven in part by basic biological urges. Pretty in pink? Sure, but "primal in pink" may be a more accurate aphorism.

Findings is a daily column by Pacific Standard staff writer Tom Jacobs, who scours the psychological-research journals to discover new insights into human behavior, ranging from the origins of our political beliefs to the cultivation of creativity.