It's a topic discussed among your friends and coworkers at least once a month, and during your own 5 to 7 day monthly flow, we can guarantee at least 3 of your friends will also be on their periods. The whole idea that your period gets on a synchronized schedule with that of other women you spend lots of time with is one that has been considered standard for as long as we can remember—or anyway, since we even started menstruating in the first place—and honestly, there was always something a little comforting knowing that you and your closest circle were all experiencing shark week together. But is it all a myth? According to a study conducted by the University of Oxford in conjunction with the Clue fertility app, probably. Clue began the study with 1,500 women, which was then narrowed down to 360 pairs who had at least three cycles over a similar time period. After analyzing the duos for at least three consecutive cycles, 273 of them ended up with a larger difference in start dates than at the beginning of the study.
"Menstrual syncing amongst the sample we had did not exist. We've also done some statistical tests and found that the difference in cycles actually grows," Clue's data scientist Marija Vlajic tells The Guardian. "This doesn't mean the pairs go out of sync—it means they were never in sync in the first place. It's the nature of two mathematical series that keep repeating: the series will diverge as the numbers grow." Only 79 of the 360 pairs ended up having a closer start date over the study, and the numbers determined that living together didn't have an effect on alignment. Realistically, there are only so many months in a year, and depending on your flow, your moon cycle is bound to overlap with that of your friend, coworker, or sister. It's easy to chalk it up to pure coincidence, but you can call us conspiracy theorists over here at InStyle HQ—lived experiences, at least among our beauty department, have us thinking that there still might be something to the communal sync.