If you’re a woman who has ever spent significant time with other women, the syncing of menstrual periods is pretty much gospel. Live with female roommates or even just see the same girlfriends on a regular basis and the phrase “Hey, I have my period, too!” becomes a regular part of conversation.
But we women have been lying to ourselves, according to science.
A new report published today by The Guardian surveys research into menstrual synchronization and finds that most studies conducted since Martha McClintock’s oft-cited survey on the subject have been unable to confirm that women’s menstrual cycles sync up when they live or spend a lot of time together.
McClintock’s 1971 study is the reason the menstrual synchronization rumor exists. Forty-five years ago, she followed 135 female college students living in a dorm together and found that for close friends and roomies, the start of their periods dropped from nine to five days apart on average the longer they lived together.
According to The Guardian, most studies that have attempted to replicate McClintock’s results found no synchronicity in women whatsoever, even in the most ideal test conditions. The report suggests that because period start dates are variable, illness, stress, weight changes, and other factors can affect the menstrual cycle. So, “synchronicity” is likely just the result of normal life shifts.
If you’re one of the 70 percent of women who believes in period syncing and loves it — don’t feel disheartened. You’ll probably sync up with your friends again at some point and you can go right back to swapping cramp-related horror stories and sharing heating pads.