There's a Tell-Tale Sign Women Are Ovulating, But You Can't See It

No, the tell-tell sign of female fertility is not the box office numbers for the ultimate ab-filled gyration-fest that is the Magic Mike sequel. As it turns out, women—at least, college-age, mostly white women in one small UK study—do show physical signs of hitting their peak fertility for the month.

These women’s faces turned redder during ovulation, but subtly enough that the human eye couldn't detect it.

As described in the journal PLOS ONE, a group of UK researchers photographed 22 women with no makeup on every weekday for a month, measuring the change in their skin tone over the course of their reproductive cycles. (None were on hormonal birth control, since it might have thrown off the results.) The researchers used a camera designed for detecting camouflage to ensure that it could accurately capture color, and measured changes using a computer program that identified the same section of the cheek in every photo. The participants measured hormonal changes throughout the month themselves. 

When the women were at their most fertile, as shown by their hormonal patterns, their skin was redder than at later stages of the ovulation cycle. But while the change was significant enough to allow computers to measure it, it wasn’t enough to be picked up by the naked eye.

This change is clearly less obvious in us than in some of our primate relatives, whose butts turn bright red when they’re experiencing estrus.

"We had thought facial skin color might be an outward signal for ovulation, as it is in other primates, but this study shows facial redness is not what men are picking up on,” study author Hannah Rowland of Cambridge University said in a press release, “although it could be a small piece of a much larger puzzle.”

Previous studies have found that men find women more attractive near the time of their ovulation (even just through scent), even if they can't quite put their finger on why. 

One study of 22, mostly white, college-age women doesn't provide enough evidence to generalize about the entire world population, so take these findings with a big grain of salt. But the study does suggest that at some point, human fertility may have been visible. Maybe this explains the enduring allure of red lipstick.