In the year 1971, Martha McClintock claimed in one of her research papers that the periods of 135 college students living together became synchronized over time.
It is often said that if girls live together in hostels, college dormitories, or families, their periods get synchronized. The question arises what is the reality behind this fact or is it just a myth that has been going on for generations? Let's know what science says in this matter.
What is the McClintock Effect?
During the year 1971, Martha McClintock claimed in one of her research letters that the periods of 135 college students living together got synchronized with time. The research revealed that the dates of onset of periods of all the girls living in the hostel gradually came closer. McClintock attributed this to the effect of pheromones (chemical signals). She claimed that pheromones leave one woman's body and affect the periods of another woman. According to this theory, when women spend time together, pheromones affect each other's hormonal systems, which brings the dates of their periods closer.
What does the new research say?
After McClintock, many researchers tried to repeat this study and the results were mixed. Many studies supported the McClintock effect while some called it a mere coincidence. Let us know what came out in different research.
Study by Oxford University and Clue App (2017)
During 2017, Oxford University and period tracking app Clue together checked the data of about 1500 women. In this study, 360 pairs were formed, which included women with close relationships such as roommates or friends. Researchers checked at least three period cycles every winter. In 273 pairs, the difference in the dates of the start of periods increased, while in only 79 pairs this difference decreased. This means that instead of periods getting synchronized, in most cases the dates of periods became different. This study revealed that living together does not increase the chances of synchronization.
Study on Chinese college students (2006)
In 2006, Zhengwei Yang and Jeffrey Shank studied 186 Chinese college students over a year. The students were placed in dormitories in groups of 4 to 8. The researchers found that the dates of the women's periods were not synchronized. Instead, the difference in the onset of periods was due to chance. The study found that periods may overlap due to differences in their duration and length, but not due to pheromones or social proximity.
Study on Indian Medical Students (2023)
The McClintock effect was supported to some extent by a study conducted on medical students in India during 2023. This study included 62 students who lived in groups of two in the hostel. Their period dates were checked for 13 months. In the results, the dates of the onset of periods were close in 54.8% of the pairs, which the researchers considered a sign of synchrony. However, the study also acknowledged that pheromones could not be separated chemically. More research is needed to confirm this.
Why is this myth so popular?
Despite mixed results, the concept of period synchrony still makes headlines. In fact, many women remember more those occasions when their periods coincided with those of a friend or roommate. They forget those occasions when it did not happen. The average menstrual cycle is 28 days, but it can range from 21 to 40 days. If two women have cycles of different lengths, then mathematically their periods can sometimes come together.
