syncFor a bodily function lots of people don’t feel comfortable talking about, menstrual cycles sure have a lot of folklore built up around them that keep getting passed down from generation to generation.

One of the most famous is that the moon affects your cycle. (You can see what the research shows about that here.)

Another is that women’s cycles sync up when they live together or spend a lot of time together so that they experience their periods at the same time–a phenomenon dubbed “menstrual synchrony”.

So, is it real? Well, let’s see what the research shows:

The idea of menstrual synchrony was first officially proposed in a 1971 study in the journal Nature. The study author, Martha McClintock, Ph.D., observed that the menstrual cycles in a small number of women living closely together in a college dormitory for three months appeared to change in length to more closely align with one another so that that the women more likely to have periods at the same time.

In later research, she proposed that pheromones–scentless chemical messengers we produce in our bodies and secrete through our sweat–trigger women’s cycles to lengthen or shorten as a way to help sync them up.

However, the results of her research have been disputed (for example, here and here) due to errors in her methods and statistical analyses.

But, not all researchers agree that errors were made in McClintock’s research.

So, over the years researchers have tried to replicate her initial findings–without much success. A 1993 study of lesbian couples showed no menstrual synchrony. A study in 2006 of female Polish students living in a dormitory for five months showed no menstrual synchrony. And another 2006 study of female Chinese students living in a dormitory for over a year showed no menstrual synchrony.

Whenever there was a change in cycles that resulted in the overlapping of periods in these studies, these studies showed it was by random chance.

So, what’s the ultimate verdict here? It may be possible that you experience menstrual synchrony with women you’re in close proximity to, but more research would need to conclusively prove it. Or it could be that your cycle and other women’s cycles may have simply varied in length naturally due to a wide number of reasons (for instance, stress, medication, intense athletic training) and, therefore, ended up randomly syncing up.

What do you think? Have you experienced menstrual synchrony yourself? Do you believe it’s something that’s real or random?

[Photo: Vishal Patel]
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