Best friends share everything, even that time of the month, reportedly. Over the past decades women have observed their periods syncing up with their close friends and roommates at some points in their lives. Although most women are familiar with this phenomenon, it still hasn’t been proven to be true.
The most promising study done to support menstrual synchronization was set up by Martha McClintock, published in 1971. Although she was able to produce results showing that many women were syncing up, scientists have since had trouble replicating the experiment;the study was repeated several times, but similar results were never collected.
The main reason for this was that the results, although they were affected by uncontrolled variables and therefore considered inaccurate. However, the variables help explain the phenomenon. The experiment was based on the assumption the synchronization of periods is a real thing, and it’s purpose was to show that close proximity alone was the cause. When other scientists tried to replicate McClintock’s, they failed because they didn’t account for other variables that could cause menstrual syncing.
McClintock cited two variables that likely affected her experiments’ outcome. People living in the same place often eat some or all of the same foods, so those women have similar nutrient levels which could affect the timing of their period. There’s also a connection between light/dark cycles and menstrual cycles: women exposed to light late at night at a certain time of the month are more likely to ovulate during said time (this explains connection between full moon and ovulation in history).
Strangely enough, neither of these are accepted explanations. The most popular reason for menstrual syncing is pheromones, which are chemical messages animals secrete that change the behavior of others. Sensing another women’s pheromones would cause a hormonal change in the body which would alter the menstrual cycle. However, McClintock did not find any evidence for this, and no one has been able to confirm the existence of a pheromone with such an effect.
Whether by chance or by a significant reason, most menstruating women have experienced their periods syncing up. The current theories on the matter haven’t been studied thoroughly enough for any solid answers.
Sources:
http://www.nytimes.com/2008/02/05/health/05real.html?scp=1&sq=menstrual%…
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