Do Women Who Live Together Have Coinciding Menstrual Cycles?

Women On A TandemThere are dozens of menstruation myths out there, ranging from the bizarre to the prosaic. Some of the more ridiculous fallacies include the belief that you shouldn’t wash your hair or have cold drinks when you’re on your period, that you are more likely to be attacked by a bear or shark when menstruating, and that you must carefully avoid all physical exertion once a month (if only that were true!). Thankfully you’ve got me to help you to separate the fact from the fiction (as far as coinciding menstruation is concerned anyway).

Coinciding menstrual cycles are also known as the ‘McClintock effect’, after American psychologist Martha McClintock’s Nature paper on the subject in 1971. The theory is that women’s cycles synchronise if they live together – supposedly due to the activity of mysterious chemicals called pheromones. Other suggested reasons for menstrual synchronisation included the effect of the moon (there is no link between lunar and menstrual cycles – women are not werewolves), social interactions, and the influence of chemicals from other women’s armpit sweat. Therefore, women who share homes with other women should expect to have their periods at the same time. Right?

Well, actually, no. There have been several studies that have investigated female proximity and menstruation, and any synchronisation is likely to be down to pure chance rather than pheromones. The length of a women’s normal menstrual cycle can be anything from 21 to 35 days, time of flow can last from 4 to 9 days, and some women choose to regulate their cycles by taking the contraceptive pill. Therefore, it would not be uncommon for a group of women living together to have some coincidental crossover, thus sometimes creating a false impression of biological synchronicity. A major study that was published in Nature in 2006 demonstrated that there was no menstrual synchronisation for 99 women living in two dormitories over five months; and this negative result has been repeated for other studies including lesbian couples and room-mates.

It therefore looks pretty certain that this menstrual cycle belief is just one more example of odd folklore.

Another old wives’ tale dispelled!

Answer by Becky Martin. Question sent from Eugene via Facebook

Yang, Z., & Schank, J. (2006). Women do not synchronize their menstrual cycles Human Nature, 17 (4), 433-447 DOI: 10.1007/s12110-006-1005-z
Stern K, & McClintock MK (1998). Regulation of ovulation by human pheromones. Nature, 392 (6672), 177-9 PMID: 9515961
MCCLINTOCK, M. (1971). Menstrual Synchrony and Suppression Nature, 229 (5282), 244-245 DOI: 10.1038/229244a0

Image credit: janwillemsen on flickr

Article by Becky Martin

June 11, 2014

Becky Martin worked as an emergency planner before deciding to live dangerously and do a PhD in disaster management at the University of Southampton instead. Occasionally she stops contemplating potential impending doom and bakes some cupcakes instead. Tweet all your catastrophe questions to her @CalamityCake.

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