Period Syncing: Scientific Myth or Shared Reality?

So there you are, enjoying a girls' night in when someone suddenly announces, "OMG, I just got my period!" Then it happens—like a twisted game of menstrual dominos—someone else pipes up: "Wait, I started mine yesterday!" And another: "Mine came this morning!"

Cue the dramatic music. You've just experienced the phenomenon known as "period syncing"—that mysterious biological event where women who spend time together supposedly start menstruating in unison, like some kind of bloody moon-based choir.

But wait—is this actually a thing? Or is it just another tall tale, like "you can't get pregnant your first time" or "eating chocolate causes acne"? At Flying Jane, we're all about cutting through the myths with a good dose of science (and humor), so let's dive into this synchronized swimming of menstrual cycles.

The Study That Started It All: McClintock and Her Army of Dormmates

Back in 1971, researcher Martha McClintock published what would become the scientific equivalent of a viral TikTok—a study claiming that women living together synchronize their periods. She gathered data from 135 college women in a dormitory and concluded that, over time, roommates and close friends started menstruating around the same time.

McClintock theorized that chemical signals (pheromones) were the invisible conductors of this menstrual orchestra. The study was published in the prestigious journal Nature, which basically gave it the scientific equivalent of a blue checkmark. Soon, "the McClintock effect" was being taught everywhere from medical schools to glossy magazines.

It was groundbreaking not just for its findings but because in 1971, scientific research on women's bodies that didn't involve reproduction or how to make better vacuum cleaners was about as common as finding a tampon machine that actually works.

Plot Twist: Modern Research Says "Yeah, About That..."

Fast forward to more recent times, when scientists armed with better statistics and larger sample sizes decided to check McClintock's homework—and found some serious red pen-worthy issues.

A 2006 study from Oxford University tracked 186 women living together in dorms (basically McClintock 2.0, but with better math) and found—drumroll please—absolutely nothing. No synchronization whatsoever. The researchers concluded that any cycle overlap was exactly what you'd expect from random chance.

Other research piled on:

• A 2017 period-tracking app study with data from over 1,500 women found no evidence of the phenomenon

• A 2019 review of the scientific literature determined that methodological flaws in early studies created an illusion of synchrony

• A study of female athletes living and training together showed no evidence of cycle convergence

Current scientific consensus: Period syncing is probably about as real as your ex's promise to change.

If It's Not Real, Why Does Everyone and Their Sister Believe It?

Despite what the science says, try telling a group of women who swear their cycles are synced that it's just a statistical coincidence. You might get hit with a collective eye roll strong enough to alter the Earth's rotation. So why does this myth have more staying power than a super-plus tampon on a light day?

• Confirmation Bias: We notice when things confirm what we already believe and conveniently forget when they don't. When your period arrives the same time as your roommate's, you high-five about it. When your periods are two weeks apart, you don't exactly send out a newsletter.

• The Overlap Illusion: Here's some math (don't worry, it won't be on the test): Menstrual cycles range from 21-35 days. With that much variation, cycles that start out different will naturally overlap at some point—kind of like how you'll eventually run into your chatty neighbor if you both go on enough walks around the block.

• The Power of Shared Experiences: Let's be real - talking about periods has historically been about as welcomed as bringing a skunk to a garden party. The ability to share this experience openly with other women creates a meaningful bond. "We're synced!" feels a lot more special than "Our cycles randomly overlapped due to statistical probability!"

• Memory Selectivity: That weekend when all three roommates were simultaneously hunting for chocolate and heating pads makes a better story than "we all got our periods at different times this month, as usual."

As Dr. Alexandra Alvergne from the Oxford study puts it: "The experience many women have isn't imaginary—it's just that it's no more common than would be expected by chance." In other words, it's like thinking you have ESP because you thought about your mom right before she called—when you forget all the times you thought about her and she didn't call.

Flying Jane is committed to evidence-based approaches to period care while honoring the diverse experiences of all who menstruate. Our products are designed to support you through every phase of your cycle, synchronized or not.

Tell us: Have you experienced what felt like period syncing? How do you feel knowing the research suggests it might be coincidental? Drop your thoughts in the comments!