If you’ve ever lived in a shared house with other women, the chances are you’ll have noticed some pretty strange goings on. We’re not talking about someone mysteriously eating your secret chocolate stash or the frankly ridiculous wait for the bathroom in the morning; we’re talking periods.

Ever since I started my period, my menstrual cycle seems to have been synced with whoever I’ve been hanging out with. While it’s nice to think that this is down to us being so in tune with each other, some experts believe it’s pure coincidence. So, which is it: science or fake news?

Back in 1971, Martha McClintock published a research article in Nature magazine called Menstrual Synchrony And Suppression, which was based on a study of eight continuous cycles of 135 women all living together in a dormitory. The study, which led to the term ‘menstrual synchrony’, concluded that women who live together or in close proximity to each other involuntarily synchronise their menstrual cycles.

So, what’s the deal?

“Women often believe that the women they live with or spend a lot of time with will have their periods at the same time,” says intimate health expert Dr Shirin Lakhani. “Anecdotally, women’s cycles do seem to sync. The theory is that your pheromones influence each other so that your periods line up.”

McClintock also hypothesised that this synchronicity is due to pheromones, the chemical substances that are produced by the body and secreted into the environment through products such as sweat. Pheromones have the ability to influence the behaviour and physiology of the same species, leading to the suggestion that our menstrual cycles can be altered by them if we spend enough time together.

A 1999 report showed that of 122 women surveyed, 84% of them were aware of the theory of menstrual synchrony, and a whopping 70% of them reported having personally experienced it. 

Like all things in nature, there’s a strong link to reproduction. One of the leading arguments for period syncing is based on the idea of ‘socially mediated synchrony’, which is basically a fancy term for women looking out for each other. The theory goes that if we’re all menstrually aligned, we’ll all be fertile at the same time, rendering it impossible for a single male to impregnate all of us at the same time.

It was believed that this was a kind of evolutionary cooperation between females to prevent a dominant male from forming a harem of fertile women, as well as protecting them from being targeted by males on heat.

Now that’s something for your Tinder bio. 

As nice a theory as it is, more recent studies do suggest that it’s more coincidence than anything else. Lakhani suggests: “If you are living with several other women, and given the duration of a menstrual cycle, the probability of some of you having your period at the same time is quite high.”

Menstrual cycle coach Roxy King agrees. “Overall, scientific studies have not been able to prove that menstruators’ cycles do sync, and if they do, it’s been put down to coincidence and confirmation bias,” she says.

In fact, what the studies do show clearly, is that women want it to be true. In one study, menstrual synchrony was noted as a positive as it creates a collective experience and offers an opportunity to feel part of a group, which is a primal human instinct. Let’s face it, when we’re feeling bloated, crampy and irritable, what we really want is someone to agree and empathise with us, not tell us how great they’re doing. 

King believes that this idea of sisterhood is key. “So many menstruators suffer unnecessarily, and it’s really nice when you find your roommate, co-worker or partner is on their period at the same time as you and you can have a moan and support each other.”

These days, it’s far easier to keep tabs on where we are cycle-wise with the advent of period apps and trackers. King explains: “There are so many variables that affect our menstrual cycles, including stress, sleep, movement, food choices, chemicals and contraceptives, which I believe have a larger influence on our cycles than just being in close proximity to other menstruators.”

But regardless of how much science tells me otherwise, I, and many other women, remain convinced that there’s something in the syncing idea. And don’t get me started on how the moon phases affect me.

Images: Getty