Living in close quarters with your lady friends has many benefits, but studies show that menstrual synchrony—synced-up periods triggered by pheromones—may not be one of them.

In her seminal 1971 study, psychologist Martha McClintock concluded that synced cycles are related to the exchange of pheromones between women in close social contact.






However, a whole crop of studies have popped up since then that contradict the “McClintock effect”—and some that claim to disprove the existence of pheromones as a whole. An Israeli research team responsible for the widest-ranging studies of human menstrual synchrony found no conclusive evidence of the phenomenon; another tightly controlled lab rat experiment disproved an existing two-pheromone synchrony model.

Just last year, McClintock’s colleague Jeffrey Schank co-authored the longest menstrual synchrony study yet, which followed a group of 186 Chinese students living in dorms for an entire year. Synch-ups did happen—but Schank concluded these were random overlaps that were bound to happen over such a long period (pun totally intended) of time.

To top it all off, after correcting for statistical and methodological errors in the initial study (and numerous studies supporting synchrony), several researchers stated that McClintock’s results were statistically inconclusive.


One uterus that'll never synch up.

In recent years, McClintock’s research has been geared toward a slightly altered definition of menstrual synchrony: it’s not so much about flawlessly linked periods, but rather how social factors affect the ovulation cycle as a whole. In 1998, her research team found that women in the beginning of their menstrual cycle secrete compounds that affect the release of luteinizing hormone (which influences the length of the ovulation cycle) in other women—and a Japanese study from 2000 is backing ‘em up.

Right now, researchers are split roughly fifty-fifty on the issue—and we can’t make a call on synched-up lady times until research conclusively sides with one camp or the other.

But until then, uterus-havers, feel free to bond over the wonder and, um, joy of flowin’ together. And stay tuned for future research, because “the fact that [synchrony] is rare,” McClintock says, “doesn’t mean that it doesn’t exist.”


Images via and

Maggie Carr has written about TV, feminism, fashion, and other kinds of lady business for BUST and Thought Catalog, among others. She's never not tweeting about Kanye West at @racecarr.

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