Next time you're running out of responses for all the "you look gorgeous!" compliments coming your way, we have a new one you could try: "Why, thank you! I'm ovulating." Increasing evidence shows that women unconsciously ramp up their beauty routines and personal style on days of the month when they're most fertile. In one study, done at the University of California's Center for Behavior, Evolution, and Culture, a group of men and women were shown photos of women taken on both high- and low-fertility days and were asked, "In which photo is the person trying to look more attractive?" The faces were digitally masked so only hairstyle, clothing, and jewelry could be observed. Photos taken in the days just before ovulation were chosen more than 80 percent of the time. And a study published in Personality and Social Psychology Bulletin found that single women in particular gravitated toward more revealing clothes on their most fertile days. "Many things determine how you choose to dress or wear your hair on any given day, but one is clearly your hormonal status," says Martie Haselton, PhD, associate professor of psychology at UCLA, who helped author both studies. "The signals we send to potential mates may be more subtle than the outward physical displays of monkeys, but that reproductive legacy lives on."
What about other times of the month? We've noticed that some women we know get very focused on their grooming habits in the days before their period. "My hair, my makeup, my skin just feel off," one colleague told us. "So I start cutting my bangs, tweezing my eyebrows, I guess in an effort to put things right." There could be another explanation for excessive PMS-related grooming: "In monkey groups, those who are stressed often engage in self-grooming as a way to comfort themselves," says Nina Jablonski, PhD, professor of anthropology at Penn State and author of Skin: A Natural History. "The touch involved in grooming has been shown to release pleasure-giving endorphins as it lowers stress hormone levels." We experience stress more acutely during the premenstrual period, she says, so the trimming and plucking may be more an effort to soothe ourselves than to spruce up our looks. But if touch is what you're after, we'd suggest getting a massage—more fun for you (and a reprieve for your eyebrows).