Period Syncing: Fact or Myth

I, as I’m sure most of you did, heard stories about periods syncing for basically my whole life. It always seemed like something everyone believed and accepted as fact. I also was told that everyone would sync to the most alpha woman in the house. One of my friends claimed that her period was always irregular but living with her roommate made it regular, along with countless other stories of people telling how they synced with people they knew.

We’ve all heard plenty about syncing, but is any of it true? Do our periods really sync with people we are around a lot or is it all a myth?

The theory behind period synchronicity is that the pheromones that we release influence those we are in close proximity with, eventually causing periods to sync up.

Periods syncing has been around forever as an old wives tale, but the first time it was mentioned in academia was in 1971 when Martha McClintock conducted a study of 135 college women living in a dorm together. She concluded that periods do in fact sync and period syncing became known as the McClintock effect.

However, this study was heavily criticized, and many said there were errors in both the statistical analysis and methodology of the study.

In 2006 there was another study conducted of 186 women living in dorms in China. From this study, they concluded that syncing did not occur and any syncing that happened was within the realm of mathematical coincidence. 

Another study in 2017 conducted by Oxford University and Clue looked at data from over 1500 people and found that there was no syncing that occurred. In fact, periods became less 'in sync' over time (which is normal for two repeating mathematical series, read more about it here).

Cycles vary in length from person to person and even from month to month. If you are around a person long enough, it makes sense that eventually your cycles will coincide. Many people suggest that the reason so many people insist that period syncing is real is because they are more likely to remember the couple of times that you and your roommate were both in pain together than the many times that you weren’t.

From these more recent studies, it seems very unlikely that period syncing is real. However, it is also difficult to prove since we don’t know how pheromones can affect periods. The variability in lengths of cycles also makes it difficult to say if people are syncing and how to even define ‘syncing up’.


Regardless of whether or not it is true, when your period is at the same time as your friend, roommate, or coworker, there’s no denying the solidarity and camaraderie you feel. Let’s all remember to support each other on our periods because we can all relate to how terrible it can be!

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