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Turns Out Period Syncing Is a Menstrual Myth

Dr. Elizabeth Yuko is the Health Editor at SheKnows. She is a bioethicist and writer specializing in sexual and reproductive health and the intersection of bioethics and popular culture. She is an adjunct professor of ethics at Fordham ...

New research suggests that spending time together doesn't make people's menstrual cycles sync up

A new study suggests that women spending a lot of time together doesn’t necessarily sync their periods — coming as a blow to lazy male stand-up comedians everywhere. Contrary to the longstanding menstrual mythology, the research found that even when women live together, they are no more likely to get their periods at the same time. In fact, women’s menstrual cycles are more likely to move apart over time.

The study, conducted by the period and fertility-tracking app Clue in conjunction with the University of Oxford, is likely the largest of its kind, which tracked 360 pairs of women. Researchers found that 76 percent of the pairs reported having a greater time difference between the start and end dates of their periods at the end of the study compared to the beginning.

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“It’s very unlikely that cycle syncing is a real phenomenon,” Clue’s data scientist Marija Vlajic told The Guardian. “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. This doesn’t mean that 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.”

So where did the idea of synchronized periods start? The idea of menstrual cycles being tied to the lunar cycle has been around for centuries (and has been the subject of empirical research) but given our old friend the period paradox (that periods are simultaneously powerful enough to be debilitating, but not worthy of our research time and funding), there haven’t been a lot of studies looking into this.

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It was a 1971 study by psychologist Martha McClintock that reinforced the commonly held menstrual/moon connection. After tracking 135 college students living in the same dorm, she found strong evidence of period synchronization — particularly in terms of the participants’ cycle start dates.

And we totally bought it. A 1999 study found that 80 percent of women believe in period synchronization, with 70 percent saying they enjoyed it.

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Admittedly, there is something empowering about this idea.

“I like the idea myself of this dominant super uterus in a group of women that makes everyone adjust their cycles,” Vlajic told The Guardian. “I can see how it gives you a special connection with a woman to go through that at the same time.”

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