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Period syncing

period syncing

Is period syncing a myth? This question has been on the Adia team’s mind recently. As a team, we spend a lot of time talking about periods, and all things women’s reproductive health. Nothing is too taboo for our office chat! For the past few months Lina and I have synced up perfectly. Lina is still breastfeeding, and so had been having pretty irregular periods, and I’ve only just started having periods again having changed my contraception. But since I’ve started my period, Lina’s cycle is now perfectly tracking mine – which is pretty handy, but also has driven a debate as to whether there is any science behind it.

This isn’t the first time I’ve experienced period syncing – there’s been university housemates, other close work colleagues, school friends – the list is pretty exhaustive. And it seems too precise to just be coincidence, or is it?

Is period syncing a myth?

In recent years science has been skeptical that period syncing is a thing. A recent study by Oxford University and the period tracker Clue –  thought to be the largest of its kind – has found data showing women’s periods do not synchronise when they live together after all. They followed 360 pairs of women. Analysing three consecutive cycles in each pair, the research found the vast majority – 273 pairs – had a greater difference in period start dates at the end of the study than at the beginning!

But talk to any woman and they will likely tell a similar story. Google it and the internet is full of similar stories.

So where did the theory start?

What causes menstrual synchrony, supposedly?

The idea actually started with research findings published in Nature, a scientific journal, in 1971. A researcher called Martha McClintock studied the menstrual cycles of 135 women in an American college.  Martha’s research found that friends and flatmates had more similar period cycles than random pairings of women.

The main theory explains this phenomenon as an evolutionary strategy. One where women co-operated with each other so their fertile windows were at the same time. This would stop men reproducing with them at once. Therefore stopping men having multiple wives and children. A form of biological sisterhood standing up against the patriarchy.

There are also some other theories that are sometimes offered up. The first is that it’s the release of pheremones that drives the syncing. However this isn’t backed up by any scientific evidence.

The second is that periods sync up to the moon. Needless to say there’s not much evidence for that theory either. 

Is period syncing a real thing?

So, do periods sync up?

In a word – no. It’s clear that science doesn’t back up these theories – yet, at least.

Then, why do friends have periods at the same time?

I can hear you yelling (and I agree). But this happens all the time! Friends always have periods at the same time.

It’s likely we are simply looking for patterns where they don’t exist. The idea that our periods sync undoubtedly creates closeness and a bond.

But a theory of synchrony, collaboration and sisterhood is certainly more interesting.

What else could impact your period?

Want to find out more about periods?

We recently held a digital meetup all about fertility with leading gynaecologist and fertility expert Dr Jess Farren. Where the topic of period syncing came up – sadly Jess reconfirmed it is all a myth. We also talk all about PCOS, endometriosis and more!


Want to understand your fertility? Adia offers easy finger-prick hormone blood tests – sign up to order yours today. The test can be done in the comfort of your own home and you’ll get the results in a matter of days.

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