Because you never go it alone.

You’ve heard the myth: whether in friend groups, at work, or even in your dorm, your period—and the periods of the females around you—may begin to sync up. Is it any coincidence when Jennifer from two cubicles down has to ask you for a tampon the same day you asked Melissa for some Midol?

What We Do Know

The story isn’t news—Martha McClintock, a psychologist at the University of Chicago, first studied the phenomenon back in 1971. In a paper published in Nature, McClintock observed that in her days as an undergraduate in an all-female dorm, the women she was around tended to get their period at the same time.

As a formal study, she asked 135 college women to track their period start dates three different times throughout the academic year. The results seemingly confirmed that women in close friend groups appear to get their periods closer together than not, and the phenomenon was dubbed the “McClintock effect.”

Since then, many researchers have conducted similar studies on people, and even animals such as hamsters and chimpanzees. A father-son team at Bar-Ilan University in Israel conducted several subsequent studies ranging from college roommates and lesbian couples to athletes, colleagues, and family members throughout the 1990’s. Their results varied: sometimes synchronicity appeared, others times not, seemingly at random.

Mary Jane Minkin, MD, clinical professor of ob-gyn at Yale University School of Medicine stated that although the phenomenon doesn’t appear to occur with any pattern, it has been observed more than once since McClintock’s original experiment. Unfortunately, there is still a lot that isn’t known about how or why this happens.

There’s a few theories out there, ranging from lunar cycles to caveman genetics, that attempt to explain the medical mystery. Of course, there’s also a group of professionals out there who discredit the phenomenon altogether.

So…Yes or No?

Although the concept of menstrual syncing has been around for thousands of years, formal research hasn’t been able to reach a conclusion either way. Despite thousands of studies and cave drawings depicting syncing, the verdict is still out.

Considering a normal menstrual cycle can vary from 21 to 35 days, and can last from 2 to 7 days, it’s not hard to see why research is difficult. Add to that the problem of some women having inconsistent or irregular patterns, and then the women who don’t have “normal” cycles, and you’ve got a whole lot of chaos surrounding one female bodily function.

Since the jury is still out, there’s no reason to double-up on the monthly supplies you buy just yet. Although your cycle may happen to align with a colleague or a roommate’s doesn’t necessarily mean it’s a science so much as mathematically probable. Either way, try to enjoy the perks of sharing a cycle: double the chocolate available to you!

If you have questions about whether or not your cycle is normal, feel free to contact us. We’d love to help with any questions or concerns you may have!