Is it really possible to sync your periods?

Women have long been told that when we live with or hang out with other females, our menstrual cycles could sync, meaning they are likely to have their period around the same time.

But one gynaecologist wants to "debunk cycle synching", which she describes as a myth, pointing out that there is no real scientific evidence to back it up.

What's more she believes it is a harmful myth to perpetuate as it "positions women as breeders that are not in control of their own body that somehow they can be affected by the herd and that they're not thinking beings."

Sharing a video clip of her discussing the issue to Instagram, Dr Jen Gunter, described the belief as the "single greatest myth" explaining that there is no real basis to prove the assumption.

"First of all, it’s been studied, so we know it doesn’t happen," she explains. "We have excellent evidence-based medicine to show it’s not true."

Instead, if you do find your cycle has synced with a friend, she says it boils down to a "combination of math (two randomly occurring events will occasionally line up) and bias."

She points out it is likely we only remembering the time our cycle matches someone else and forget "all the times it did not".

"Also, we are often off by a few days in remembering the date of our last period, so that could factor in as well," she adds.

The theory behind the syncing of menstrual cycles is that women's pheromones interact when they are in close proximity, causing them to have their period at the same time.

But Dr Gunter has a response to explain that too.

"No one has actually ever proven the existence of human pheromones," she explains. "I know the perfume industry would have you think otherwise, but no one has proven they exist."

Is period syncing really a myth?

Anecdotally, many those who menstruate believe that period syncing is a real thing that occurs. Certainly, while living with our close friends we'll recall times when we were sharing period products at the exact same time.

But what's the truth?

"The notion that women's menstrual cycles can synchronise when they live together, often referred to as the 'McClintock effect' or 'menstrual synchrony', has been a subject of interest and debate since first proposed in a 1971 study by Martha McClintock," explains Mr Hemant Vakharia, consultant gynaecologist and advanced laparoscopic surgeon at London Gynaecology.

The study suggested that close proximity, such as in dormitories, could lead to synchronised menstrual cycles among women, possibly through pheromones. However, Mr Vakharia says subsequent research has produced mixed results, with many studies unable to replicate McClintock's findings.

"A review of the literature indicates that the evidence for menstrual synchrony is not conclusive," he continues. "A study in 1992 aimed to correct statistical errors in McClintock's original study and concluded that biases in previous studies led to a perceived higher frequency of menstrual synchrony than actually existed."

Another study involving 64 Japanese women in a dormitory found that while some women did synchronise with their roommates, the overall evidence was not strong enough to conclusively support the phenomenon.

"Moreover, a 2017 study, at Oxford University, using an app to track menstrual cycles among pairs of women found that most pairs' cycles diverged rather than converged over time, suggesting that menstrual synchrony might be more of a myth than a scientifically supported fact," Mr Vakharia continues.

Critics of the menstrual synchrony theory argue that mathematical probability and the natural variability in menstrual cycle lengths can explain why cycles of women living together might occasionally overlap, giving the impression of synchrony.

"It's important to note that factors such as stress, illness, and lifestyle changes can influence menstrual cycles, potentially contributing to the perception of synchronisation," Mr Vakharia explains.

"In summary, while the idea of menstrual synchrony has been popularised in both scientific literature and popular media, the current consensus among researchers is that there is no substantial evidence to support the notion that women's menstrual cycles synchronise when they live together.

"The phenomenon appears to be more coincidental or perceived due to overlapping cycles rather than a result of pheromonal or other biological influences."

While doubt has now been cast over its existence, as with many women's health issues, (see also menopause, endometriosis, PCOS), further research is needed to fully explore the menstrual synchrony theory.

Until then, however, period syncing will likely live on and continue to be passed down as an anecdotally proven belief about women's periods.

Periods: Read more

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• More than a million women keep period sick days a secret (Yahoo Life UK, 6-min read)

• Government set to abolish tax on period pants (Yahoo Life UK, 3-min read)

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