Is There Any Science Behind Period Syncing?

If you are a menstruators and have friends who are also menstruators, then you must have at least once in your life experienced your cycles syncing! It is exciting. But is it really scientific? The idea of period syncing is called menstrual synchrony or the McClintock effect, which suggests that many menstruators who spend a lot of time together, their cycles start aligning due to pheromonal influence. Some also believe that "alpha females" in a group can set the timing for others' cycles.

The McClintock Effect: How It All Started?

The idea of your period syncing with other menstruators has been passed down for generations. However, it only gained its scientific attention in 1971, when Martha McClintock, a psychologist, conducted a study on 135 college women living in the same dorm. The study then tracked the start of their menstrual bleeding, however, their ovulation or other cycle factors were not tracked. McClintock concluded that the women's cycles were syncing over time and it lead to the phenomenon being named after her as McClintock effect. The findings were published in 1971 in Nature journal. However, the study had its own limitations and modern research had questioned its validity.

What Does The New Research Say?

With the rise of period-tracking apps, researchers have been able to analyze much larger data sets. More recent studied do not however support this period syncing theory.

A 2006 review of menstrual synchrony published in journal Human Nature analyzed data from 186 women in dormitories in China and found no evidence of syncing. The study suggested that any synchronization was purely mathematical coincidence.

Another 2017 study published in the Journal of Menstrual Cycle Research found that 44% of women living together reported experiencing some form of menstrual alignment. The researchers noted that the factor could be a shared lifestyle, such as diet and stress that could play a role. They also found that women living together experienced similar period symptoms, including menstrual migraines even when their cycles did not sync.

The next study was one of the largest studies on period syncing conducted by Oxford University in partnership with the period-tracking app Clue, which analyzed the data from over 1,500 people and found no evidence of menstrual synchrony. The study was published in journal Nature Digital Medicine in 2017 and concluded that women living together do not influence each other's cycles.

What Does Influence Period Then?

Some believe that menstrual cycles sync with lunar cycle because the average menstrual cycle length which is 28 to 30 days is similar to moon's cycle, which is 29.5 days. A 1986 study found that 28% of women had their period during new moon. The study was published in American Journal of Obstetrics and Gynecology. Whereas another 2013 study published in Endocrine Research found no strong link between the moon and menstruation.

If Period Cycles Sync, Why Is It So Difficult To Prove?

There may be several reasons why science cannot prove a link between syncing cycles. The role of pheromones is unclear. As they are chemical signals that influence behavior, attraction and reproduction, however, no solid evidence can be found that they actually alter menstrual cycles.

Menstrual cycles to vary greatly. The average cycle is 28 days, but normal cycles range from 21 to 40 days. Bleeding also varies, as for some people, it lasts for 2 days, for others, it lasts for 7 days. This variation makes "syncing" difficult to define.