Does My Period Sync With Other People's Cycles?


cycle synching

Cycle synching… go ahead and say that 5 times fast.


But for real, what is it? Well, cycle synching is a phenomenon first studied in 1971 that has been noted for many years by menstruators. This phenomenon is the theory that the menstrual cycles of 2 or more people will synchronise when physically close to each other for lengths of time. Cycle synching is often noted between close friends, family members, or people living in close quarters with each other. Basically, any time menstruators spend lengths of time around each other, the theory is that their period cycles sync up and happen at the same time, whether they were due for it or not. I have personally believed in cycle synching for ages, as a close friend of mine has what we jokingly call a “moon uterus”, because every time a person with a uterus is around her, they get their period. I wish I was being dramatic or hyperbolic, but it truly seems like magic. Nobody else’s cycle can overpower hers, and people have been known to get their period within a week of ending their cycle because they spent too much time around ‘the woman with the moon uterus’. It turns out, much to my initial disbelief, that cycle synching has been debunked by scientific studies and is simply just a myth or an old wives tale - but there is so much more to the phenomenon, so let’s dive in.


The first time cycle synching was studied was by the Department of Psychology at Harvard University was in 1971 by Martha K. McClintock. This preliminary study, titled “Menstrual Synchrony and Suppression” detailed the synchrony and suppression of menstrual cycles within a group of women living together in a college dormitory. It set out to understand the effects that social interaction can have on menstrual cycles, and determined that there was a connection between time spent together and menstrual syncing, stating, “The significant factor in synchrony is that the individuals of the group spend time together”. The study then continues to explore the duration of each cycle in relation to the exposure to others but was inconclusive as to how or why this phenomenon occurred, stating “Whether the mechanism underlying this phenomenon is pheromonal, mediated by awareness or some other process is a question which still remains open for speculation and investigation”. So basically, to put it simply, the study was scientifically inconclusive but showed what seemed to be true evidence of the phenomenon occurring, but never why it occurred.

can my period sync up with my friends

So, again, we are left to wonder if cycle synching is just a way for us menstruators to sympathise with each other or if it’s truly a scientific wonder. Well, sorry to burst your bubble, but it turns out there is no factual evidence that your cycles are synching (This news is gonna be hard to break to ‘the women with the moon uterus’. Ugh). In 2017, menstrual tracking app, Clue, conducted a study that concluded that menstrual cycle synching was “unlikely”. This study debunked all suggestions from the 1971 study, including the myth of the “alpha uterus” (so… moon uterus), and the common assumption that living together or spending lengths of time together would change or disrupt a cycle. In fact, it took our assumptions and ran in the opposite direction, proving that cycles are actually more likely to diverge, rather than sync, over time.


I know what you’re thinking… this doesn’t make sense. How can so many people be so sure that this exists, including historical studies along the way, but now you’re saying that it doesn’t? Well, we could get into the psychology of it all, how the mandala effect might coerce us into believing something that isn’t there, or how energy and gravity and crystals and all that good stuff could be the reason why we truly believe in cycle synching, but to put it simply, it’s just science. As access to study groups and tracking information from thousands of menstruators became available through tracking data, the information was more widely available to study and understand.


The phenomenon is still believed to be true by many, and quite frankly, it is impressively under studied in the world of science. There are many people who believe that cycle synching undoubtedly occurs. If you ask me, I still fear my friend with a moon uterus when I don’t want to be bleeding, even if the studies say it’s not true.


period sync

For now, I leave you with this – cycle syncing is something I whole-heartedly believed in until I looked into these studies, so I’m glad I had the opportunity to learn. Cycle synching is also still widely believed to be true, and as long as it’s not harmful, I don’t see an issue with labelling one of your friends with a moon uterus and moving on with life. Just don’t leave them out of plans for fear of cycle synching, please.



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