If you have ever lived or worked closely with other people who have periods, you may have sometimes noticed that you’re both suddenly feeling the effects of your PMS around the same time, or both you and your roommates are washing & drying your period underwear the same week. You may have found yourself on numerous occasions asking yourself, and each other, if your periods have synced, or even being adamant that they have. But is there actually any science to back up the theory? Do our menstruating pheromones actually speak to each other and align to the same rhythm, or do we find comfort in sisterhood solidarity and believe our periods have edged closer together for comfort?


 Period sync



For decades cycle syncing was nothing more than an old wives tale, passed down from mothers to their off-spring for generations. Menstrual health has been overlooked for so long by the scientific research community it was not until 1971 that it first appeared in a medical academic paper. Researcher Martha McClintock spoke to and followed the cycles of 137 women all living in university dorms, and found evidence to believe that their cycles had synced up. She concluded: “the evidence for synchronicity is quite strong", indicating that in humans there is some "interpersonal physiological process which affects the menstrual cycle.”


However, further down the line, a new study, one of the largest to be conducted, by the cycle tracking app Clue, in partnership with Oxford University; Studying 360 pairs of women living closely together, analysing three consecutive cycles for each pair, has concluded that women’s periods don’t sync together at all when living together. In fact, due to their research they conclude that based on varying cycle lengths women’s menstrual cycles are more likely to diverge than come together over time.

Speaking about the phenomenon Clue’s data scientist Marija Vlajic commented, “It’s very unlikely that cycle syncing is a real phenomenon. Menstrual syncing amongst the sample we had did not exist. We’ve also done some statistical tests and found that the difference in cycles actually grows. This doesn’t mean that pairs go out of sync – it means they were never in sync in the first place. It’s the nature of two mathematical series that keep repeating: the series will diverge as the numbers grow.”





The theory behind the syncing of menstrual cycles is that women's pheromones interact when they are in close proximity, causing them to have their period at the same time. So with evidence from research over the last decade now neither confirming nor completely disproving the phenomenon of cycle syncing, why do so many of us still believe that it happens, some quite adamantly, despite no medical proof.

With most people’s cycles being an average of 28 days, the chances of you being on your period at the same time as one of your close friends is likely. As the stigma and taboo about openly discussing periods dissipates, you are more likely to have conversations about your time of the month in order to be able to fully decipher if you’re on your period at the same time, however is it due to pheromone syncing or pure coincidence.

That being said, many of us can personally account for times when we have lived in the same house as another person who gets their period and seen genuine results of your periods syncing up and getting closer together, especially over a longer period of time.

There are some women that even affirm that certain “alpha females” can be the influential factor when entire groups of women experience ovulation and menstruation synced. However, as with the cycle syncing phenomenon itself, medical literature doesn't have a solid case to prove that it happens, in spite of observational testimonials from groups of menstruators.


So despite what generations of menstruators have passed down to us, and even our own experience of seeing genuine syncing with your close proximity females, there is yet to be any conclusive evidence or research to determine that our pheromones are in fact influencing each other and syncing our cycles for female solidarity. 



Photo Credits: Cristina Gareau 







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