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Talk True is a 91���� limited series for medical myth-busting. With each episode, we’ll talk to medical professionals about commonly misunderstood health issues to get the actual facts.

Eight out of ten babes probably share this experience: They were living with other ladies for a while, and suddenly, they realised their menstrual periods had synced.

It’s such a widespread notion that one hardly knows when or how it started; we’ve just come to accept it. But is it based on scientific fact or tales-under-the-moonlight material? An practitioner, Mary says it’s more of the latter.

What’s period syncing?

“We weren’t taught period syncing in medical school, and that’s largely because it’s not backed by extensive research,” Mary says.

Period syncing describes a popular belief that women who didn’t have synchronised periods before will begin to when they stay in close proximity long enough. It’s also known as or the McClintock effect.

Dr Martha McClintock was the OG babe who started it all. In 1971, she studied a group of 135 women living in a college dorm and concluded that the female communicate with each other due to physical closeness, triggering period syncing. 

Something about the moon?

Period syncing isn’t limited to close proximity with other women. Other claim menstrual cycles also sync with lunar cycles, meaning that periods can be tracked with the different moon phases.

, if menstruation starts during the full moon phase, it’d mean the woman is most fertile during the new moon — a claim Mary insists has no scientific basis.

“It’s a thing in some cultures — definitely not common in Nigeria, though — but no, you can’t sync with the moon.”

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It all comes down to mathematics and coincidence

Mary explained that, while there’s little scientific evidence to prove syncing is due to hormones or lunar cycles, there’s actually a valid mathematical explanation.

“Women have different menstrual cycles, and over time, they’ll overlap. For instance, I have a 28-day cycle. This means I won’t start my period on the same day of each month because my cycle doesn’t span a complete month. I can start on the 15th of month one and start on the 18th of the following month. I may even see my period twice in the same month. This probability is higher in those with 26-day cycles, and if such a person is your roommate, your periods will overlap at a point. 

It’s different from someone with a complete 30-day cycle who always menstruates on a particular date. Even then, if you live with someone with a different cycle length, overlapping is a possibility.”

It also explains the moon thing. When the early people — read as “our ancestors” — still relied on lunar calendars, it was just natural to track the menstrual cycle with the lunar cycle as both share an approximate average of 28 days. It wasn’t universal, as there would’ve been women with different cycle lengths, but it kinda worked. Again, mathematics.

What do current findings say?

Quite a number of recent studies have debunked the McClintock effect.

“A and by Oxford University provided data which demonstrated how unlikely it is for women to disrupt each other’s menstrual cycles just by being in close proximity to one another.”

What can actually affect your period?

Since science has agreed that your female bestie doesn’t pose a threat to your menstrual cycle, here are some of the factors Mary confirms can actually affect your period.

“Stress and medication due to certain chronic illnesses can either delay your period or bring it on early. Birth control pills also alter the levels of certain hormones in your body — specifically progesterone and estrogen — and these control when, or if, you see your period.”

The takeaway

Menstrual cycles don’t converge; they diverge — increase indefinitely — during the course of life. If you do feel a connection with the other women in your life, it’s probably a coincidence. 

However, if you’ve “synced” with the women you live with before and then experienced an “out of sync” period, it doesn’t mean anything is wrong with your cycle.

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