Period Syncing Probably Isn’t Real

“time-lapse photography of moon” by Linda Xu on Unsplash

A very persistent belief among many people who have periods is that when they spend enough time together, especially when sharing a home, their menstrual cycles synchronise. This phenomenon is presented as fact in the media and even in sex education classes. However, while there has been scientific interest in period syncing for a few decades now, it remains controversial.

So what’s the evidence for and against period syncing, and why is the idea so appealing?

The evidence for period syncing

The concept of period syncing first entered the public consciousness in 1971, when Martha McClintock published a paper showing that the periods of college roommates synchronised over the duration of four months. One possible mechanism, which was explored further in subsequent studies, was that physical proximity between the participants facilitated the exchange of pheromones, which then induced changes in their menstrual cycles. Other researchers have claimed that emotional closeness, rather than physical proximity, is the driver of period syncing, although the exact mechanism in this case is even more obscure.

Apart from McClintock’s seminal paper, there is some more evidence that period syncing does occur. Weller and Weller, based at Bar-Ilan University in Israel, have carried out many studies on…