By Macaela Mackenzie. Photos: Getty Images, Hannah Choi/Allure.
Science has bad news for that biological bond of sisterhood you feel when you and your work wife realize you’re on the same period schedule: period syncing isn't real. According to a new study from period-tracking app Clue and the University of Oxford, the idea that your cycle syncs with the people you spend the most time with doesn’t actually have any scientific foundation.
The idea that menstrual cycles sync comes from a 1971 study that proposed the existence of an "alpha uterus" with such great hormonal power it could influence less dominant uteruses around it to ovulate and menstruate in unison. In the past, researchers theorized that this might have something to do with mating season: perhaps women sync up to level the playing field, making it so all women are sexually out of commission at the same time.
To test this theory with actual data, Clue looked at 360 pairs of users who volunteered for the study, including roommates, siblings, friends, mothers and daughters, partners, and colleagues. Researchers gathered data about the timing of the pairs' periods over three consecutive menstrual cycles using the Clue app. They also took into account whether pairs lived together and eliminated any pairs using hormonal birth control (meaning they were artificially adjusting their cycle).
By the end of the three successive cycles, the cycles of 273 of these 360 pairs were actually farther apart than at the beginning, and the gap between cycles narrowed for only 79 of the pairs. What's more, the average difference between all pairs' cycles was 10 days at the beginning of the study and 38 days at the end. So much for the sisterhood sync. Clue also concluded that living together didn’t seem to have any effect on whether people's cycles synced up or diverged, finding that 37 percent of the diverging pairs were roommates and only 24 percent of the syncing pairs were.
The good news is that even if your uterus isn’t showing solidarity with your crampy, PMSing kin, you still can. All it takes is a good old-fashioned "I feel your pain" and a purse stocked with ibuprofen.
This story originally appeared on Allure.
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