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05th Mar 2024

Is period syncing a real thing? Here’s what science says

Anna Martin

period syncing

Do you find that you and your best friend get your period at the same time?

Or do you and your sister end up sharing an all-knowing look when you both reach for the painkillers on a random Friday?

Roommates, coworkers, same-sex couples, and family members who start their period on or about the same day every month can feel like this is evidence of closeness or a signifier of just how much time they spend together.

Even though this is a popular belief, there isn’t a lot of evidence to back it up and some experts even debunk it as myth.

What is period synching?

period syncing
Credit: Getty

Period syncing is also known as “menstrual synchrony” and “the McClintock effect.”

It’s based on the theory that when you come in physical contact with another person who menstruates, your pheromones influence each other so that eventually, your monthly cycles line up.

The first study on this phenomenon came about in 1971 when a Harvard researcher by the name of Martha McClintock studied the menstrual cycles of a small sample of women living in college dorms, aged 17 to 22.

The study didn’t test other cycle factors, like when the women ovulated, but it did track when the women’s monthly bleeding began.

McClintock concluded that the women’s periods were, indeed, syncing up and the term “McClintock effect” was born.

So is it real?

 period syncing
Credit: Getty

Well, more recent research was carried out and it seems to suggest that period syncing isn’t a real thing.

A study carried out in 1993 found that 29 same-sex couples who both had periods did not experience syncing and on top of this a 1995 study of pairs of close friends who did not live together also did not experience it.

In more recent years, a 2006 study  of the literature made the assertion that “women do not sync their menstrual cycles”.

The data on which they based their conclusion was gathered from 186 women living in groups in a dorm in China.

Any period that appeared to occur was within the realm of mathematical coincidence according to the researchers.

In 2017 another study, this time on a much larger group was conducted by Oxford University and the period tracking app company, Clue.

It was the biggest blow to the theory of period syncing as the data from over 1,500 people demonstrated that it’s unlikely that women can disrupt and change each other’s menstrual cycles by being in close proximity to one another.

Though many of us have experienced our periods syncing with our besties, the science just doesn’t seem to exist in backing it up.