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Do You & Your BFFs Really ‘Sync Up’ On Your Period? Menstruation Experts Get Real With Us

The previous semester of college I lived with five other menstruating people, and at one point I swore our periods lined up. We spent so much time together that it honestly didn’t shock me that eventually we began menstruating simultaneously. And it was honestly the perfect excuse to eat cartons of Ben & Jerry’s as we binge watched all three ‘High School Musical’ movies. It was hormonal chaos at times, but it was definitely a bonding experience. 

You’ve either heard of this phenomena before or you’ve probably experienced it: Period syncing. Period or cycle syncing is essentially when people menstruate at the same time after being in a relationship with each other or living close together. 

But why does this actually happen? It seems to be a pretty common thing that happens all the time with people you are close to like your mom, your besties, your roommates, or evening your siblings. According to a 1999 study, it’s officially called “menstrual synchrony”, and at the time, 70 percent of women said they’ve experienced and enjoyed it. Well apparently it’s all in our heads, because experts now say that this isn’t actually a thing


The reason why so many believe in menstrual synchrony is due to a 1971 study published in the journal Nature by Harvard University psychologist Martha McClintock. She looked at the menstrual cycles of 135 female undergraduate students who lived in the same dorm between the ages of 17 and 22 years old. For one year she tracked each woman’s cycle and found that roommates or close friends had joint cycles. The study, dubbed the McClintock Effect, suggests that an “alpha uterus” possibly influences this cycle synching. 

According to Obstetrician-gynecologist at the Cleveland Clinic Lynn Simpson, there really is no scientific evidence to back this up though. “For healthy people living together, proximity doesn’t change cycle timing or frequency,” she said on the clinic’s blog. “Periods just don’t work that way.” 

In 2017 the app Clue, which helps track your period, asked app users about their period synchrony to find out more about this phenomenon. Out of 1,500 responses, there were only 360 pairs with at least three cycles. Researchers then analyzed three consecutive menstrual cycles of those pairs, and 273 of those started to actually diverge from each other. They found that most women who thought their periods were syncing up were actually starting at different times. 

Data scientist’s from Clue told Her Campus that just because there is no evidence for it doesn’t mean that it never happens. “It’s probably because our brain likes to look for patterns. If you have a friend and your friend tells you that they’ve got their period, if you don’t have your period at that particular point, that’ll be a piece of information that your brain won’t necessarily notice. But if you have your period when they mention that they do, your brain is more likely retain this information, and remember it, should the same scenario occur again,” said CEO of Clue Ida Tin.

She also says you’d only recall the times when you’re cycles overlap and not the times when they don’t. 

All the times you’ve actually synced up with your friends really breaks down to math. There are 28 days within a cycle, and your period can last for a couple days to an entire week. When you have large group of friends, there are only so many times you could menstruate. At some point, the timing will eventually lineup or overlap. 

“On a more human level, we’re may be naturally inclined to want to believe in the notion of our cycles syncing as it makes us feel more connected with those close to us,” Tin said. 

Even if it’s not an actual thing, it’s great to know that your friends can literally feel your pain. During your time of the month, they can have your back and support your week long chocolate addiction. 

Carissa Dunlap is a Her Campus News X Social Intern for Summer 2018. She is a current Publishing major and Journalism minor at Emerson College (Class of 2020). When she isn't perusing the YA bookshelf at the bookstore, she can be found watching dog videos on Facebook, at her favorite coffee shops, or relaxing on the beach. Follow her on Instagram @dunlapcarissa or Twitter @Caridunlap.