Menstrual Cycles Among Female Roommates: Is Synchronization Fact or Myth?

This is my second year living in an apartment with three other girls, and it's been a fun (and interesting!) experience that I wouldn't change for anything.  My roommates are open about pretty much everything, which usually provides for some hilarious conversations.

Today, my one roommate asked if I was on my period because she had gotten hers several days early and she figured my menstrual cycle was "messing her schedule up." When I told her I hadn't gotten mine yet, she was confused.  A few hours later, she came up to me and explained that one of our other roommates had gotten hers, so that explained why she got hers early.  Yep, just a normal day at my apartment.

So this whole conversation got me thinking: does menstrual synchrony even exist?  We'd been operating on this assumption for two years now that our menstrual cycles were "synced up." We've actually discussed how one of our menstrual cycles may be controlling the schedules of everyone else in the apartment.  Is this even true?  

In searching for answers, I found a 1971 study done by Martha McClintock of the Psychology Deparment at Harvard.  The study (which was published in Nature) consisted of 135 participants between the ages of 17 and 22 who lived together in a women's college dormitory.  The subjects were asked several questions related to their menstrual cycle at three points throughout the school year (like the duration of their cycle, when it started, etc).  Room arrangements and proximity between certain subjects was also taken into account.  They were asked how much time they spent with males and which girls in the dorm they spent the most time with.  Women were considered "close friends" by the McClintock if they both said they spent a lot of time with one another.  The results of the study showed there was a strong correlation of synchronization between roommates and close friends.  

In the study, McClintock discussed synchronization of female mice and female primates in studies done before hers.  She believed that this had to do with pheromones, or kind of chemical release that acts a signal to members of the same species. According to McClintock, there could be a possible third variable causing the synchronization, like the seasonal changes in type of food the women were eating (considering they were all living at college together, the seasonal changes in the food would impact anyone who ate at a common dining facility).  But in my apartment, we all eat different things.  None of us cook together because we all have different preferences and cooking abilities.  Additionally, one of my roommates is a vegetarian, so she can't eat a lot of the things we would cook anyway even if we were to the same meals, so the pheromone argument holds more weight with me. 

ph 1.jpg

Then, I found this review by H. Clyde Wilson, a professor in the Department of Anthropology at the University of Missouri.  Basically, it refutes the result of McClintick's 1971 study based on faulty experimental design.  He explains that, even though two experiments and three studies showed the same results as McClintock, four other studies did not show similar results.  According to Wilson, the three biggest problems that usually plague menstrual synchrony studies are:

(1) failure to recognize that a probable one-half of the  pairs  in  a sample synchronize  by  chance

(2)  miscalculation  of the  absolute  difference between initial  menses  onsets  

(3)  exclusion  from  the  sample  of those subjects  or some onsets  of subjects  in  order  to  fit  the  number  of  onsets  to  the  specifications  of  the  research 

Plus, there's still a lot of speculation about whether or not pheromones actually exist in humans.  Disproving the existence of human pheromones would probably discount McClintock's argument altogether.

So, with that being said, I'm not sure that I found a definitive answer to my question as it seems to be a debate that is still ongoing.  In the meantime, I'll try to shift the conversations in my apartment away from such controversial scientific debates such as this to slightly easier discussions, like whose turn it is to take out the trash.


I have notice this as well among my friends. Once, there was 4 of us on our cycle starting in the same week. We ended up fighting and breaking ways for about 2 weeks before we could stomach seeing each other again, it was quite hilarious. Although, I do think that it might be something as a scientific as pheromones or maybe something as simple as psychology. It seems to me that the mind is a powerful thing, and the more we focus and think about something the more possible it becomes. Think of how drastic the effect in an experiment can be changed just telling the test subject what the desired results are. Interesting enough, I believe the same can be applied here as well. Knowing that you're friend is currently on her cycle, we empathize and our body responds accordingly.

It’s so interesting that someone actually chose to post a blog about this, because some of my friends and I were discussing this exact idea yesterday. I live in the dorms on a sorority floor full of girls and about 8 of the girls (at least that we knew of) began their cycle at the exact same time. It’s so strange how that seems to happen. In addition, in high school, I went to a three week dance program and even just in that short amount of the time, the same thing happened as well. I had always believed that the longer girls spent time together, the more likely they were to become synchronized. This, however, made me reconsider if the amount of time the girls spend together is even a factor. While the girls in my sorority live together the entire school year, the same synchronizing was able to happen in just a three week period. But if it’s not the amount of time spent, what is it? While doing my own research, I found an article that concluded things similarly to you. It also claimed that there was no actual scientific proof of physical or hormonal synchronization in menstruation. It’s hard to believe that this is so when so many instances of it have happened to so many individuals. Perhaps in the future, doctors or scientists will be able to tell what really causes this mysterious synchronization.

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