How do periods sync up

Advertising Policy. You have successfully subscribed to our newsletter. Related Articles. Why Is My Period Late? Tired of Tampons? But as much as some of us may want to believe our periods sync up and celebrate that feeling of camaraderie, that doesn't been there's any solid scientific evidence that it happens.

For over 40 years, researchers and doctors have tried to answer that question with mixed findings — but these days, the science community is fairly confident that period syncing isn't a thing.

Keep reading to understand how they came to that conclusion, what we've learned over the years, and where more research is needed. In , Harvard doctor Martha McClintock studied a group of women living in a college dorm. Since , multiple studies have been conducted on female roommates, best friends, lesbian couples, and even animals to see if menstrual cycles actually converge while spending time together.

In a study , McClintock, along with Kathleen Stern, announced that they had "definitive evidence" of the McClintock Effect, proving that human pheromones could manipulate the timing of ovulation. But Beverly Strassman, professor of anthropology at the University of Michigan, used their assertion to inform her paper in Human Reproduction , arguing the opposite while analyzing cycle length:. By chance alone, one would expect two women to be 7 days apart half of 14 days.

Given that menstruation can last 5 days, overlapping periods are a common occurrence. That women synchronize to each other, however, is a myth. The first scientific evidence of period syncing came about in , with the "McClintock study.

Pairs with close proximity were grouped together as "closest friends" or "roommates" — and pairs that had no relationship were used as the control. The study found that, after six months, those who were in close proximity to each other had their periods start three to seven days apart whereas the control group periods started five to 15 days apart.

However, other researchers found the study's analysis to be flawed , and many have since disregarded its findings. Subsequent studies conducted in the s found conflicting evidence about period syncing.

A study found that 29 same-sex couples who both had periods did not experience syncing. A study of pairs of close friends who did not live together also did not experience period syncing.

In , period tracking app Clue teamed up with Oxford University to better understand cycle syncing. They analyzed the cycles of pairs of women who knew each other well and tracked their cycles through the app.

The results found that after three cycles, of the pairs actually saw a larger difference in their cycle start date than they did at the beginning of the study — which would indicate that period syncing doesn't occur. It's important to note that the study was not peer-reviewed , which means that outside medical experts haven't signed-off on the study's methodology or conclusions. Some academics recently decided to find out if the findings of synchronicity of periods could be put down to chance.

They looked at six years' worth of data of the menstrual cycles of our close cousins, baboons. Where the patterns are explained by chance.

The researchers compared how much each model would account for the data being observed. They found that the model assuming that patterns would appear by chance was the best model by far. More research could be carried out in the future that does reveal evidence that women's periods sync.

But currently many researchers are sceptical. Additional reporting by Elizabeth Cassin. Image source, iStock. Find out more. Image source, Getty Images. Did the idea of synchronised menstruation reflect the emergence of the feminist movement in the s? Image source, Science Photo Library.