By Alexandra Alvergne, University of Oxford.
It is a popular belief that women who live together synchronise their menstrual cycles, and that it’s mediated by their pheromones, the airborne molecules that enable members of the same species to communicate non-verbally.
The idea originated in a study published in Nature in 1971, which recorded data on the onset of menstruation for 135 American college students living in a dormitory. The dorm had four corridors each with around 25 girls living in single and double rooms.
Based on the analysis of around eight cycles per woman, the study reported an increase in synchronisation (a decrease in the difference between onset dates) for roommates and among closest friends, but not among random pairings in the dormitory.
The author hypothesised that this was driven by the amount of time that women spent together, as this would allow for pheromone communication.
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Since then, so-called “socially mediated synchrony” has been intensely studied in various groups of women, such as roommates, co-workers, lesbian couples and women from high fertility populations, and in a number of animal species, including rats, baboons and chimpanzees.