You've heard of periods supposedly syncing. We found out if one woman's hormones can influence the periods of everyone around her

By Rachel Jacoby Zoldan
April 20, 2016

You've probably heard that if you spend enough time with the same women, your menstrual cycles will all sync up. Some of us can even swear that it can-and actually does-happen. (Have you ever worked in an office full of women? We have!) But is there an alpha uterus controlling us all when it comes to getting in sync? (BTW, here's What Your Period Means for Your Workout Schedule.)

First off, the whole idea of periods syncing in the first place has limited evidence at best, says Rebecca Nelken, M.D., a board-certified OB/GYN in Los Angeles. "It dates back to 1971 when psychology student Martha McClintock realized that women who lived together in a dormitory ended up on similar menstrual cycles," says Nelken. The research, which was published in the journal Nature, specifically theorized that pheromones affected the hormones of the women causing the synchronization. Problem is, this wasn't a randomized clinical trial, "it was more of an observational study," says Nelken. Real-world translation? Take this study-as you should with most one-off studies-with a large grain of salt.

Beyond this study, there are only theories as to why one's women's pheromones are more potent than others (and there's not much definitive research on pheromones in general, says Nelken). For example, there are theories that women who are more fertile are so-called leaders in terms of cycling, but Nelken is quick to point out there's no research there.

The other common colloquial explanation is that more powerful women-say, boss-lady type CEOs-secret more powerful pheromones and thus would be the one for everyone's cycles to sync to. "Nothing's been scientifically's hard to imagine the survival advantage that would be conferred by this," she says. "I can't think of a reproductive advantage either." And since there's no kind of Darwinian selection at play, the medical community hasn't sought to further their knowledge on this topic, says Nelken. (Uh, Why Are Women Putting Pot In Their Vaginas?)

"Ultimately, we just don't know if there's such thing as an 'alpha uterus,' cycles syncing up, and whether it's indicative of health, fertility, or power," says Nelken. So next time you realize you synched up with your roommate, don't think twice about it. The good thing is that you can split a box of super-taxed tampons. (Related: Why Is Everyone So Obsessed with Periods Right Now?)