Periods are a natural cleansing process of the women’s body that occurs approximately every 28 to 30 days. Although the dates of periods vary from woman to woman, there is a common belief—which is very popular among women living together in PGs, hostels, flats or shared houses—that: “My periods have started, so yours will also start soon.” In scientific language, this phenomenon is called *McClintock Effect* or *Menstrual Synchrony. In fact, it has been believed for years that pheromones (a type of chemical) released by women living nearby affect each other’s menstrual cycles. But is this really a fact, or just a coincidence? Let us know what modern research and medical experts say on this matter.
What is the McClintock Effect?
According to the Cleveland Clinic, this theory related to synchronization of menstrual cycles was first introduced in 1971 by psychologist Martha McClintock. In 1971, Martha conducted a study on 135 female college students and claimed that, over time, students who were roommates or close friends had their periods move closer to each other. In other words, the ovulation times of women living nearby gradually start matching each other. According to their hypothesis, pheromones released through sweat travel through the air to the other woman’s hormonal system and activate it, causing the timing of ovulation and menstruation to change until they become completely “in sync.”
What do doctors say?
According to Dr Nupur Gupta, Senior Consultant, Department of Obstetrics and Gynecology at Fortis Memorial Research Institute, Gurgaon: “The notion that the menstrual cycles of girls or women living together in hostels, PGs or shared houses will necessarily be out of sync has not been scientifically proven. This is entirely a matter of chance. The duration of every woman’s menstrual cycle is different; hence, it is quite natural that, over time, their dates “Sometimes they can match or overlap each other.” This in no way means that their bodies or menstrual cycles are actually ‘in sync’ with each other.
A study conducted by Oxford University and period tracking app ‘Clue’ analyzed data from about 360 girls and women (who all lived together). The results showed that instead of their periods coming closer together, the gap between their menstrual cycles actually increased over time. Researchers say that no solid scientific basis has been found to prove the theory of “period syncing”. A study published in the National Library of Medicine in 2006 looked at 186 Chinese women who lived together; The results revealed that what appears to be syncing may be due mostly to a mathematical coincidence and natural variations in the menstrual cycle.
Lifestyle is the real reason
Dr. Nupur believes that menstrual dates sometimes being similar may be due to lifestyle factors rather than pheromones. Women who live together or nearby often have similar stressors. Apart from this, their eating habits and physical activity levels are also quite similar. This same routine affects their hormonal balance. Research shows that if two friends follow the same diet and workout routine, it is possible that their hormones may be affected in the same way. This is why menstrual dates sometimes match—a phenomenon people often mistake for “syncing.”
Experts say that every woman’s menstrual cycle is different; While one woman’s cycle may be 21 days, another’s may be 35 days. When two or three women with different cycle lengths spend time together, it is inevitable that their menstrual dates will coincide at some point in the month. Rather than calling it actual “sinking”, it would be more accurate to call it a “coincidence”.
