Can Women Really Sync Their Periods?

Live in a house-share with more than one other cisgender woman and you’ll almost certainly come across the concept of menstrual synchrony, which is, basically, the theory that women who spend a lot of time together eventually sync their periods. Meaning they’re PMS-ing and period-ing at the same time. When I lived in a house with four women, our two male housemates did not care for period week, during which they’d be subject to three days of PMS followed by four days of us lying on the sofa with hot water bottles, watching crap movies and crying. Obviously we hammed it up – we were unbearably basic. The trouble is, actual real-life scientific research tells me that we probably didn’t sync our periods. Because there’s very little evidence to show that menstrual synchrony is A Thing. Have I over-romanticised my memories of sharing a house with loads of other girls that much? The answer, unfortunately, is probably yes. Undeterred, I gave gynaecologist Dr. Gedis Grudzinskas, a.k.a. a non-cape-wearing hero who has previously said that women should get time off work for periods, a call. He’ll get it, I thought, desperately remembering all the times my housemate had groaned, “I’m getting my period” and I’d gone, “OMG me too.”

Sadly, though, he tells me that the evidence for menstrual synchrony is “not good”. “It’s a very attractive idea,” he says, “But the data doesn’t support it. The original idea was based on soft data which, subsequently, hasn’t been repeated.” Rats. This “original data” came from a study carried out in 1971, when Martha McClintock studied 135 women living in university dorms and found that, over the school year, close friends' period start dates went from an average of 6.4 days apart to 4.6 days apart. “A group of women living together in a college dormitory suggests that social interaction can have a strong effect on the menstrual cycle”, she wrote. The problem is, since then, we haven’t been able to come by those results again. In 1991, more women in college dormitories and cooperative houses were studied and in 1993, a study involving lesbian partners was conducted. Both failed to find any evidence of menstrual synchrony.

This is disappointing. Not just because, by talking about menstrual synchrony as fact for most of our lives, we’ve all been helping to perpetuate a scientific myth grounded in very little truth. Oops. No, what’s most deflating is that we, as humans, are naturally empathetic and showing that we understand another person’s pain is one way of forging a connection. Now, it turns out, those connections might have been based – to use the current buzzword – on fake news. SAD. McClintock’s theory as to why women might sync their periods involves pheromones – and her reasoning does make sense. “The theory is that through pheromones we could subconsciously identify a certain hormonal status of an individual and therefore our body is influenced by it," Dr. Grudzinskas says carefully. "But it’s just a hypothesis and not proven." But ask any woman and I’m certain – I’M CERTAIN – they'll say they've experienced menstrual synchrony. Myself included. An old housemate of mine had what we colloquially called a "mother womb" – within two days of being around her, other women would swear their cycles had matched with hers. I tell Dr. Grudzinskas about her. “She could make a lot of money if she was actually doing that!” he laughs, not unkindly. So why are we so convinced it happens? Are there other factors we're misreading? One explanation might go back to that urge to empathise. Could we be picking up the mental symptoms of PMS subconsciously? “We human beings are supportive of each other and the basic concept is, a burden shared is a burden lessened,” Dr. Grudzinskas says. While this could potentially be the case psychologically, he adds, sharing physical pain is less likely. Alternatively, a change in cycle could come about through symptoms of extreme stress – like moving into a new house. “Severe stress causes our body to go into what I might call a 'survival mode'," he says. "Things that aren’t essential for our immediate survival begin to shut down and ovulation might be one of those." Moving into a new house with a new set of women, where new friendships have to be established – there might be an element of 'subconscious stress' there which, theoretically, could stop our periods, altering the menstrual cycle. Grudzinskas is pretty sceptical about this, though, and says the person in question would have to be under “quite extreme stress”. Hmm. So sounds pretty unlikely all round, then. Either way, until it's disproved, I would like to keep on secretly hoping that menstrual synchrony is really a thing. Because, let's face it – when you're feeling like a pile of rubbish, it's nice to know someone else is right beside you, feeling the same thing.