Period Syncing: Real or Myth?
Period syncing describes a popular belief that women who live together or spend a lot of time together begin menstruating on the same day every month. However, no research evidence supports that this happens.
What is period syncing?
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.
Some women even swear that certain “alpha females” can be the determining factor when entire groups of women experience ovulation and menstruation.
The McClintock effect
The idea of period syncing has been passed down from mothers to their daughters and discussed in dorms and women’s restrooms for centuries. But the scientific community started to take the idea seriously when a researcher named Martha McClintock conducted a study of 135 college women living in a dorm together to see if their menstrual cycles aligned.
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. After that, period syncing was referred to as “the McClintock effect.”
But what does current research say?
With the invention of period tracking apps that store digital records of women’s cycles, there’s a lot more data available now to understand if period syncing is real. And the new research doesn’t support McClintock’s original conclusion.
In 2006, a new study and review Trusted Source of the literature made the assertion that “women do not sync their menstrual cycles.” This study collected data from 186 women living in groups in a dorm in China. Any period syncing that appeared to occur, the study concluded, was within the realm of mathematical coincidence.
A large study conducted by Oxford University and the period tracking app company Clue was the biggest blow yet to the theory of period syncing. Data from over 1,500 people demonstrated that it’s unlikely that women can disrupt each other’s menstrual cycles by being in close proximity to one another.
A much smaller 2017 studyTrusted Source keeps the idea of period syncing alive by pointing out that 44 percent of participants that were living with other women experienced period synchrony. Period symptoms like menstrual migraine were also more common in women living together. This would indicate that women might influence each other’s periods in ways beyond the timing of their menstruation.
As with many women’s health issues, menstrual synchrony deserves more attention and research, despite how difficult it may be to prove or disprove. Until then, period syncing will probably continue to live on as an anecdotally proven belief about women’s periods!