If you’re living with or constantly in the company of other people with periods, you may have experienced period syncing. The myth has been passed on for decades, but while it may seem harmless, it’s a good idea to find out what science has to say about period syncing.
What do studies say?
A researcher named Martha McClintock conducted a study among 135 female college students living in dorms to see whether their menstrual cycles are in sync. McClintock asked the students to track when their monthly bleeding began.
Upon comparing the results, McClintock concluded that their menstruations are in sync, and called it as the “McClintock effect.” However, McClintock’s study did not test other factors such as the students’ day of ovulation, as well as stress, diet, and other factors that are known to affect menstrual cycles.
Furthermore, several subsequent studies disproves the McClintock effect. A study in 1993 found that 29 same-sex couples did not have syncing periods. And in 1995, another study of pairs of close friends who did not live together also did not experience syncing.
A new study in 2006 also proved that “women do not sync their menstrual cycles.” It was conducted among 186 women living in groups in a dorm in China. The study concluded that any syncing occurred was purely mathematical coincidence.
Lastly, In 2017, a popular period tracking app teamed up with Oxford University to better understand cycle syncing. The study analyzed — with the help of the app — the cycles of 360 pairs of women who knew each other well. The results revealed that “after three cycles, 273 of the pairs actually saw a larger difference in their cycle start date than they did at the beginning of the study.” Thus, concluding that period syncing doesn’t occur.
So, is period syncing true? Most studies show that it’s just coincidence and disprove the phenomenon. However, researchers believe that it deserves more attention since it has yet to be medically confirmed or debunked.
Remember that there are a lot of factors that can affect the menstrual cycle. Simply being “out of sync” with your friends or family doesn’t mean that something is wrong with your cycle or your relationship with them.