To menstruate often means navigating a maze of truth and misconception. Can someone swim during their period? Yes, they can. Does menstrual scent lure bears? It does not. There is one long-standing rumor, however, that many find appealing: the belief that people who spend significant time together will have their menstrual cycles align, a concept known as menstrual synchrony. Over the years, several friends have insisted that my cycle influenced theirs.
I remember hearing that when I was growing up, says Dr Rachel Jensen, Darney-Landy fellow at the American College of Obstetricians and Gynecologists. She notes that the idea resonates because it evokes a sense of closeness. The thought that our bodies could harmonize with those around us feels comforting and unifying.
Despite this emotional appeal, the body does not function in that way. Below is what is known about this widespread misconception.
Is menstrual synchrony real
It is not supported by science.
The concept gained traction in the early 1970s when Dr Martha McClintock published the first study suggesting that students living in the same dormitory showed convergence in their cycles. This observation became known as the McClintock Effect.
Research in the 1990s appeared to support her findings, with some studies proposing that pheromones or other scent signals might speed up or delay cycles.
More recent studies, however, have been conducted with stronger research methods, and these have not found reliable evidence of synchrony among people living together, says Dr Jewel Kling, chair of womens health at the Mayo Clinic in Arizona.
Scientists have also not identified any biological pathway that could cause such an effect. There is no known biological mechanism that would make menstrual cycles sync, Jensen says.
Why do so many people believe in menstrual synchrony
According to Dr Salena Zanotti, OB GYN at the Cleveland Clinic, the belief remains widespread.
If cycles appear to align, experts say the explanation lies more in cognitive bias and probability than physiology.
People tend to remember the cycles of those they are close with, Jensen explains. When two cycles overlap, the coincidence becomes noticeable. Because cycle lengths naturally vary, the chance that two will occasionally coincide is statistically high. Studies show that overlap occurs at the rate expected by probability alone, Jensen says.
What influences menstrual cycle timing
Experts note that many factors can affect the timing and duration of a menstrual cycle. These include:
- Body composition: higher BMI is linked to cycle irregularity, says Kling.
- Age: cycles may fluctuate during adolescence and near menopause, Jensen notes.
- Psychological stress: depression can disrupt cycle patterns.
- Medication: including hormonal birth control.
- Medical conditions: such as thyroid disease, polycystic ovarian syndrome, and menopause.
- Lifestyle: smoking, alcohol, caffeine, diet, and physical activity.
Other widespread menstrual myths
Zanotti says many menstrual misconceptions stem from cultural beliefs, such as the idea that periods are unclean or shameful.
She notes another common myth: that using tampons or menstrual cups affects virginity, which is not true.
Jensen adds that there is no medical reason to avoid sex or exercise during a period. Both are safe, though the risks of pregnancy and sexually transmitted infections still exist. Physical activity can also help reduce symptoms such as cramps or mood shifts.
While myths often circulate easily, important facts remain less discussed. Kling points out that conditions like painful periods, abnormal bleeding, and premenstrual physical or emotional symptoms are extremely common. Up to 85 percent of women experience some form of menstrual related condition, she says, and a significant portion find it disruptive.
Zanotti emphasizes that menstrual discomfort should not be accepted as inevitable. Periods are a natural part of life, she says. If someone experiences severe or persistent symptoms, seeking medical care can provide support and treatment options.
Although the belief in menstrual synchrony is generally harmless, Jensen reminds that following inaccurate health advice can have real consequences. If you hear something from social media or a friend, it is wise to check with a medical professional before accepting or sharing it, she says.