January 20, 2022

Does Your Period Really Sync With Close Friends?

Is it the moon, pheromones or coincidence?

woman tracking her cycle on her calendar

Almost every woman can tell the same story: She was living at home or in her college dorm, and her menstrual cycle synced up with another woman’s.

It’s a widely known wives’ tale, and many theories suggest that outside factors can push menstrual cycles to shift. But, does scientific evidence actually exist to back it up? Ob/Gyn Stacie Jhaveri, MD, says no.

“For healthy people living together, proximity doesn’t change cycle timing or frequency,” she says. “Periods just don’t work that way.”


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

What is the ‘menstrual myth’?

Stemming from a 1971 study published in Nature, the menstrual synchronization myth — called the McClintock Effect — suggests that pheromones or other factors can influence and shift periods for women who live together.

The results, based on observations of 135 Wellesley College students, have long been questioned. While a few studies had similar findings, many who duplicated Martha McClintock’s study think there were methodological errors, as well as statistical errors, in the analysis.

Throughout the decades, numerous studies have been debunking this myth over and over, including a 2006 Human Nature study that showed that menstrual cycles don’t align reliably after a year of living together.

Do pheromones or the moon’s phases have anything to do with my period?

Alongside the McClintock Effect, researchers have investigated whether the phases of the moon can push a woman’s period to start earlier or later in the month.

“Although the moon’s pull affects the ocean’s tides, there’s no verifiable evidence to date that the moon can affect the ebb and flow of your menstrual cycle,” says Dr. Jhaveri.

Besides moon phases, researchers wondered if human pheromones and periods can be linked together. Pheromones are chemicals released by animals that influence the behavior of others of the same species. Among animals and insects, a lot of evidence exists to support the power of pheromones to impact and change hormonal behaviors.

“It’s possible that the same effect exists in humans, but there’s no research to support that claim,” says Dr. Jhaveri. “Pheromones are largely emitted from the armpits and the groin, but think about the habits of modern-day society. Maybe there’s something there, but if you’re washing it all off when you shower, the pheromones aren’t going to have much effect.”

When mathematics come into play

Science may not confirm a chemical or hormonal reason to explain why your period might match up with a roommate or close friend, but there is a mathematical explanation: It’s simply a matter of time. Over time, a woman who has a three-week cycle and another who has a five-week cycle will eventually see their periods overlap.

“It’s anecdotal that you’re likely to remember the times you had bad cramps at the same time your roommate did more than the times you didn’t,” says Dr. Jhaveri. “You will overlap and diverge because women have different cycle lengths.”

If you live with someone for at least a year, your cycles are likely to happen to occur together a few times.


What really can affect your period?

While science can’t prove whether living with someone or the pull of the moon impact your cycle, there are a few things that can change the timing of your period:

  • Birth control pills. The pill alters the levels of progesterone and estrogen in your body to control when — and if — you have a period. You can manipulate when your period arrives, so it’s essentially a fake period. Note that other medications can affect your period, too.
  • Extreme stress. Constant worry or anxiety over life or work problems can sometimes delay your period or bring it on early.
  • Chronic illness. Living with constant health problems, as well as taking certain medications, can make your period irregular.
  • Anorexia/bulimia. Highly restrictive control over caloric intake — either too high or too low — can impact whether you even have a period.
  • Exercise. Your period can disappear if you don’t fuel your body properly during intense exercise.

Although many women may feel an elemental connection with roommates or close friends, it’s probably just a coincidence when your periods happen to sync up.


Related Articles

Male with eyes closed sitting hunched over, pinching area between their eyes
January 29, 2024
Headache and Fatigue: 11 Possible Causes That Can Trigger Both

Many factors, like dehydration, a cold or even your medication, can result in these common symptoms

woman in discomfort lying down on couch
November 5, 2023
What Is ‘Period Flu’? How Your Period Can Cause Flu-Like Symptoms

Hormonal changes are the likely culprits behind the aches and fatigue before your period

female getting a shot in arm
July 26, 2023
Will a COVID-19 Vaccine Throw Your Period Off?

Irregularities in cycle length and flow aren’t a cause for concern

woman with hormonal acne along cheek and jaw
July 25, 2023
The Breakout Breakdown: Why You Get Acne Around Your Period

Hormone fluctuations impact oil and sebum production, creating painful, tender pimples

female at gynecologists' appointment
June 28, 2023
Can You Go to Your Gynecologist Appointment When You’re on Your Period?

Typically, you can keep your appointment, let your gynecologist know and let your worries go

Person holding tampon by string.
May 9, 2023
What’s the Best Tampon Size To Use?

It depends on your menstrual flow, and a little trial and error

woman checking menstrual cycle on calendar
April 19, 2023
8 Reasons Why Your Period Is Late

Stress, extreme diet and exercise, PCOS and, of course, pregnancy could be responsible

Woman sitting on a couch browsing on her laptop
April 6, 2023
Yes, Weight Loss Can Impact Your Menstrual Cycle

If your period hasn’t come for three months, it’s best to see a doctor

Trending Topics

close up of keto gummies
Do Keto Gummies Work for Weight Loss? Are They Safe?

Research is inconclusive whether or not these supplements are helpful

Person in yellow tshirt and blue jeans relaxing on green couch in living room reading texts on their phone.
Here’s How Many Calories You Naturally Burn in a Day

Your metabolism may torch 1,300 to 2,000 calories daily with no activity

Older person postioned sideways showing dowager hump.
Dowager’s Hump: What It Is and How To Get Rid of It

The hump at the base of your neck may be caused by osteoporosis or poor posture