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Studies have long shown that men are more attracted to women when they’re ovulating, but how guys sense that it’s baby-making time has never really been clear.
A group of British researchers may have cracked at least some of the code. After an elaborate study that monitored 22 women throughout their menstrual cycle, the researchers learned women send out visual cues when they’re ovulating. But here’s the twist — the cues are undetectable by the human eye.
Women’s faces, they observed, redden just a touch when they’re ovulating. That facial redness, the researchers believe, was once most likely an involuntary sign that women were entering the most fertile phase of their cycle. As humans evolved, women’s faces got less red during ovulation, but modern men are somehow, almost mystically, still responding.
The research was recently published in the open-access journal PLoS ONE, and it’s the most complete objective study of female faces during the ovulatory cycle to date. To perform the study, twenty-two women were photographed without make-up at the same time Monday through Friday for at least one month in the same environment. Researchers photographed them with a scientific camera modified to more accurately capture color — the same kind used for studying camouflage in wildlife.
A computer program was designed to select an identical patch of cheek from each photograph. The women also self-tested for hormone changes at key times throughout their cycle, as dictated by the research team,
When the team monitored color levels and changes, they found that facial redness varied significantly across the ovulatory cycle, peaking at ovulation and remaining high during the latter stages of the cycle after estrogen levels had fallen. Skin redness then dipped considerably once menstruation began. Unfortunately, the researchers declined to share the women’s photos, noting that the differences wouldn’t be detectable.
But if it is all happening on a level the human eye can’t see, what are men responding to?
"Women don't advertise ovulation, but they do seem to leak information about it," said Dr. Hannah Rowland, from the University of Cambridge's Zoology Department, who led the study with Dr. Robert Burriss, a psychologist from Northumbria University.
"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, although it could be a small piece of a much larger puzzle," she said.
Humans, like other primates, are attracted to red, the study’s authors say. They wondered if women subconsciously bolstered the undetectable facial redness during ovulation by wearing more blush, or even dressing in red clothes.
"As far back as the 1970s, scientists were speculating that involuntary signals of fertility such as skin color changes might be replaced with voluntary signals, such as clothing and behavior," said Burriss.
Or, maybe it’s just a vibe women give off.
During ovulation, studies show, women blush more when they’re around men they find attractive. "Other research has shown that when women are in the fertile phase of their cycle they are more flirtatious and their pupils dilate more readily, but only when they are thinking about or interacting with attractive men," said Burriss.
"We will need to do more research to find out if skin redness changes in the same way."