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What is period syncing? -

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

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The idea has existed for centuries -

The idea of period syncing has been passed down from mothers to their daughters, and discussed with friends and family for centuries.

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Research -

The first scientific evidence of period syncing came about in 1971, with the McClintock study.

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The McClintock effect -

Martha McClintock, a researcher at Harvard University, analyzed the menstrual cycles of 135 women living in college dorms, aged 17 to 22.

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The McClintock effect -

Pairs with close proximity were grouped together as closest friends or roommates, and pairs that had no relationship were used as the control subjects.

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The McClintock effect -

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.

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The McClintock effect -

But the study didn't test other cycle factors, like when the women ovulated. However, it did track when the women's monthly bleeding began.

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A flawed study? -

Because the study lacked the additional cycle factors, other researchers found its analysis to be flawed, and many have since disregarded its findings.

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Is period syncing a myth? -

Other studies conducted in the 1990s found conflicting evidence about period syncing. A 1993 study found that 29 same-sex couples where both had periods didn't experience syncing.

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Further research -

A study from 1995 looked at pairs of close friends who didn't live together, and the results showed that they didn't experience period syncing either.

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The largest study conducted -

In 2017, period tracking app Clue teamed up with Oxford University to better understand cycle syncing.

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Big data -

They analyzed the cycles of 360 pairs of women who knew each other well and tracked their cycles through the app.

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A surprising result -

The results found that after three cycles, 273 of the pairs actually saw a larger difference in their cycle start date than when the study started. This means that period syncing didn't occur for these pairs.

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The study wasn't peer-reviewed -

It's important to note that the study by Clue and Oxford University wasn't peer-reviewed, which means that outside medical experts haven't signed off on the study's methodology or conclusions.

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Why do women experience period syncing, then? -

McClintock theorized that pheromones, natural chemicals that send messages from one person to another, could be linked to period syncing.

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McClintock's theory -

McClintock believed that period syncing may have less to do with close female interactions and more to do with close female friends being exposed to male pheromones at similar times.

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Male and female pheromones -

One study found that women exposed to male pheromones saw an increase in the hormone responsible for triggering ovulation. But there still isn't much evidence that connects pheromones and period syncing.

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It's still controversial -

Period syncing is controversial because experts still don't know for sure if the pheromones McClintock theorized on can actually influence the start of your period.

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Period syncing is hard to prove -

Period syncing is also difficult to prove because of the logistics of women's period cycles.

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Periods are different for everyone -

While the standard menstrual cycle lasts for 28 days, lots of people don't experience periods that way. It can be a very different experience for people who menstruate.

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Each cycle is different -

That's because cycle length varies from person to person. Some people have their period every 21 days, while others see their period begin every 35 days.

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Each cycle is different -

Some people experience bleeding for a week, while others only bleed for a day or two.

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Each cycle is different -

Some people have regular periods, while others have cycles that are less regular.

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It's a subjective metric -

Due to the fact that each cycle is different, period syncing might to be a subjective metric that depends on how we define "syncing up."

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Laws of probability -

Menstrual synchrony might often appear due to the laws of probability more than anything else.

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Period syncing -

If you have your period for one week out of the month, and you live with three other women, two of you will probably be having your period at the same time.

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There's nothing wrong if your period is "out of sync" -

But do keep in mind that if your period is "out of sync" with the women you're the closest with, that doesn't mean anything is wrong with your cycle or your relationships.

Sources: (Healthline) (Insider) 

See also: The gender health gap—times medicine failed women

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