To be someone who menstruates means continuously trying to untangle fact from fiction. Is it true that you can’t swim on your period? No. Does the scent of a person menstruating attract bears? Also no.
There is one period rumor I’ve always kind of enjoyed, though: when women are in close proximity for long enough, their menstrual cycles will eventually sync up, also known as “menstrual synchrony”. I’ve had several friends over the years claim that my period had yanked them on to my cycle.
“I remember hearing that from family members when I was younger,” says Dr Rachel Jensen, Darney-Landy fellow at the American College of Obstetricians and Gynecologists. Jensen says she understands why this belief is so popular: “The idea that our bodies would synchronize with those we are close to is comforting and connecting.”
But the body doesn’t actually work that way. Below, what you need to know about this common myth.
Is menstrual synchrony real?
No.
The idea gained a lot of attention in the early 1970s, when Dr Martha McClintock published the first scientific paper on menstrual synchrony. In it, she observed students living in a college dorm, and determined that women who live in close proximity or share a common environment experience a convergence of their menstrual cycles. This became known as the McClintock Effect.
A number of subsequent studies in the 1990s confirmed McClintock’s finding. Some suggested that the shift may be the result of “olfactory cues” or pheromones which accelerate or delay the menstrual cycle.
But more recent studies that have been “more rigorously designed” have “generally failed to show any synchrony between menstrual cycles in women living together,” says Dr Jewel Kling, chair of women’s health at the Mayo Clinic in Arizona.
And research has failed to show how the body would even trigger this effect. “There isn’t a biological mechanism for menstrual syncing,” says Jensen.
Why do so many people believe in menstrual synchrony?
“Many women think this is true,” says Dr Salena Zanotti, OB-GYN at the Cleveland Clinic.
If it seems like people’s periods are syncing up, that’s the result of information biases and statistics rather than biology.
We are more likely to know and remember the menstrual timing of those we are close with, Jensen says. This means that if our cycles sync up, we are more likely to notice.
Since menstrual cycles vary in time and length, it’s statistically likely that the cycles of two people will eventually overlap, Jensen says: “Studies show that cycles sync up at the same rate as we would expect based on mathematical probability due to chance”.
What affects menstrual cycle timing?
Many factors affect the timing and duration of one’s menstrual cycle, experts say. These include:
Body composition: a high BMI is associated with irregular cycles, says Kling.
Age: “Menses can be irregular in adolescents and as people approach menopause,” says Jensen.
Psychological stress: depression can disrupt a person’s cycle.
Medication, such as birth control.
Medical conditions, such as thyroid disease, polycystic ovarian syndrome or menopause.
Lifestyle factors, such as smoking, alcohol and caffeine consumption, diet and physical activity.
What are other common menstrual myths?
Many menstrual myths are cultural, says Zanotti, like the idea that periods are dirty or embarrassing.
She also points to the myth that using a tampon or a menstrual cup means that one is not a virgin. (Not true.)
Nor is it true that people should not have sex or exercise while on their period, says Jensen. “Both are safe, though people should be aware that there is still a risk of STIs or pregnancy while on their period,” she says, adding that exercise can help with certain period symptoms like cramps or mood changes.
Such menstrual myths seem to propagate freely, while some facts remain under-discussed. Kling says that menstrual-related conditions such as painful menses (dysmenorrhea), abnormal uterine bleeding, and physical and psychological premenstrual symptoms are very common. “Up to 85% of women experience some menstrual-related syndrome,” she says. “And 40% report being significantly bothered by them.”
It doesn’t have to be this way, says Zanotti. “Periods are a normal way of life,” she says. “They do not have to be very painful and very heavy.” If one struggles with their cycle, she suggests seeing a medical provider to help manage it.
Although the myth of menstrual synchrony is relatively harmless, Jensen notes that “there can be serious consequences if people follow inaccurate health advice.”
“If you see or hear something on social media or from a friend, it is always a good idea to check with your doctor before acting on it or even passing it on,” she says.
