Can your period really sync with your BFF?

Blood Sisters: Myth or Reality? 
By: Haley Guerin

        You’re having a bit of a crummy day–– your clumsy ass spilled that delicious vanilla latte all over your white pants, you feel bloated AF, and to top it all off, you hardly got any sleep last night. So, of course you do what one does when having a bad day: you call your bestie. You tell her about your rotten day and that it’s all happening because of your period and guess what? In true bestie fashion, she just got her period too! Like a metaphysical affirmation from the universe that is basically saying you and your bestie are made for each other, you feel like blood sisters. We have all experienced something like this situation in which our menstrual cycle syncs with one of our friends. But can we really “sync up”? Are we really blood sisters?

        In a study performed in 1999, 80% of womxn were found to believe in period syncing and 70% of womxn stated that they enjoy it when it happens––talk about a menstrual community, folks! These attitudes seem to be consistent with those of modern menstruators. But how well do these attitudes line up with the hard facts? If you’ve ever researched this question on your own, you probably came across something called the “McClintock effect” which is basically just a fancy way of saying period syncing, deriving from a famous study performed by a womxn fittingly named Martha McClintock. Her study sparked the conversation and research about period syncing because it was the first of its kind.

        McClintock’s study was carried out at an all female institution called Wellesley College, located on the outskirts of the Greater Boston area in Massachusetts. Here, McClintock studied 135 college womxn who lived in the same dorm. In her study, she found that roommates and close friends experienced period syncing while random pairings of womxn did not. She suggested that these results were due to womxn’s pheromones communicating with each other when womxn were spending a lot of time around each other, causing their cycles to sync up. Yet, McClintock’s experiment faced a critical flaw: she did not account for chance in the syncing of periods amongst womxn. McClintock’s study has been disproven by several modern research efforts that have failed to replicate her results. 

       A similar study was carried out in 2006 in a womxn’s dorm in China and the study displayed the exact opposite results: womxn’s cycles actually did not sync up at all. Additionally, there were nearly two hundred Chinese womxn living in this dormitory compared to the 135 in McClintock’s study. Still not convinced that cycle syncing is a myth? Check out the work of Beverly Strassman at the University of Michigan. In her research paper, Human Reproduction, Strassman explains how the monthly time frame that periods operate in make them susceptible to aligning with each other (not to be confused with cycle syncing which implies non-randomness). She writes, “If the menstrual cycle is 28 days long, then 14 days apart would be maximal asynchrony. By chance alone, one would expect two women to be 7 days apart (half of 14 days). Given that a menstruation can last 5 days, overlapping periods are a common occurrence. That women synchronize to each other, however, is a myth.” This helps explain why we observe this phenomenon so often and why it is often mistaken for cycle syncing. 

        The idea of period syncing is exciting and can even conjure up a sense of camaraderie amongst womxn. However, as far as modern research goes, this phenomenon is a myth despite what many womxn believe. The timing in which our menstrual cycles take place make them highly susceptible to aligning with that of other womxn. So while we may not be blood sisters, it doesn’t mean that we cannot continue to support each other and talk about periods! Get out there and spread the bloody word!


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