Do Women Really Sync Their Period Cycle When They Spend Lots Of Time Together

Ladies in close proximity all get their periods at once, right? A full 95 percent of women say they believe in such “menstrual synchrony,” yet the science is suspect.

Yes, one study found that women living in the same dorm bled in unison, but follow-up studies haven’t been able to replicate that result.

“Still, anecdotally, we see this all the time,” says Alyssa Dweck, M.D., who points out that women who cohabit often have similar diet, exercise, and sleep behaviors—all of which can affect cycles.