Myth Busting: Menstrual Synchrony

Almost every menstruating person has experienced it: you spend too much time with your friend and suddenly you both have your period, even though you’re not due for a couple of days. “We’ve synched,” you think, as many other people do when they experience the same phenomenon, but is this caused by biological mechanisms, or are ‘synching periods’ just a myth?

The idea of women syncing up has long been used in media for comedic purposes, mainly to draw attention to the now even higher tensions when there is not just one person PMSing, but two. Not only that, but it is also used to show how close two characters are, since syncing up is thought to be the ultimate bond.

But as much as we’d like to blame our friend for bringing about our period at some inconvenient time, multiple studies have proven that period synchronization is actually a myth. But how can this be? Surely all the times you’ve randomly synched with your roommate or best friend must be the primal, animalistic, and spiritual bond that all women share, right?

Wrong. Many different studies have been conducted on the topic of “menstrual synchrony,” and have come back inconclusive of any scientific support for the occurrence. But in 1971, McClintock introduced the idea of period synchronization into the public consciousness with her study of the menstrual patterns of college women, and although it didn’t hold up scientifically, the theory stuck in peoples’ minds.

“Menstrual Synchrony and Suppression,” as it appeared in the journal Nature, was a two-page scholarly paper that studied a group of 135 women living in an all-female college dormitory. The data collected during the next year found an increase in synchronization between the women’s menstrual cycles as the term progressed, especially between closer friends and roommates. The beginning of the study found an average of six and a half days’ difference between the period start dates, and by the end found an average of four. This information was widely circulated and quoted in other scholarly journals, upholstering the hypothesis that menstrual synchrony was a biological response to increased socialization of menstruating peoples.

Though two studies were conducted after McClintock’s that supported her findings, more and more dissenting papers were published afterward, poking holes in her methodology and various oversights. Most importantly, the vast majority of studies replicating her experiment did not support the hypothesis that period syncing was anything other than a legend.

The truth is, with the 28-day menstrual cycle, a quarter of the time you are bound to sync up with any other menstruating person. Though it may feel magical, inspiring, or even just annoying to sync up with your best friend, there truly is nothing biological about it. Although the period synchronization theory is not scientifically supported, it is still generally accepted by the public, due to the appealing narrative that unites women and their inner mechanisms, as well as the opportunity to exploit the phenomenon for comedic jabs at PMS.

Perhaps one of the most popular tropes concerning period syncing is the mythical, yet all-knowing, “alpha uterus.” This is the idea that one uterus can possess so much hormonal power that it pulls all surrounding uteruses onto its schedule, but this too is not scientifically supported.

So although menstrual synchrony is floating around somewhere with unicorns and bigfoot, that doesn’t mean that you can’t still find solidarity with your fellow menstruator–that time of the month is difficult for everyone who experiences it, and having a close companion be in it can almost feel fated. And even with all of this new information you’ve learned about the myth of syncing, you can still pretend you didn’t read this and get mad at your sister for making your period come early.