Menstrual synchrony: Fact or fiction?

Hey Alice,

Okay, so my mother does not believe, as I do, that when a group of women live closely together (i.e., in a dorm setting) that their menstrual cycles become roughly similar, due to the release of pheromones. I'm pretty sure that I heard this somewhere, but I can't find anything to back it up. I swear I'm not making it up, but my mom doesn't believe me.

Thanks for your help.

— Hopes She's Right

Dear Hopes She's Right,

You and your mother aren’t the only ones debating the facts surrounding menstrual synchrony (the tendency of women's menstrual cycles to converge). A heavy flow of controversy has existed since 1971, when a researcher studied the menstrual cycles of menstruating women living in the same residence hall. The findings suggested that there were factors, such as pheromones, that influenced the timing of a person’s period, causing it to shift and synchronize among women who live together. Researchers who have tried to replicate this study indicated that there may have been some methodological errors in the original study design. Furthermore, recent research on menstrual synchrony doesn't support the 1971 finding. What’s likely happening is that individuals with different menstrual cycle lengths live together long enough that there are times when their periods occur at the same time.  

While it’s unlikely that pheromones are shifting the timing of menstruation, there are some other factors that might have an impact:

  • Birth control pills: The birth control pill operates by altering the levels of progesterone and estrogen in the body, thereby influencing if, and when, menstruation occurs.
  • Extreme stress: Having high levels of stress, worry, or anxiety can lead early or late periods.
  • Chronic illness: If living with a chronic illness or taking certain medications, it may cause periods to be irregular.
  • Eating disorders: Anorexia, bulimia, binge eating, and other calorie-controlled patterns of eating can impact the timing of periods or whether it even comes.

List adapted from Cleveland Clinic.

Until more is known about good ol’ Aunt Flo, it’s difficult to definitively say whether menstrual cycles can sync up. In the meantime, you can check out the various studies on the topic, or you can start your own investigation among your close friends to see how you all align.

Here’s to getting on the same page, if not the same cycle!

Last updated Jul 05, 2019
Originally published Jun 22, 2001

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