Does menstruation synchronize with other women?

Families with several women are sure that their rules are in sync and they all have them in the next few days. Is it true that menstruation sticks between women or is it a myth?

The theory behind the timing of menstrual cycles is that women’s pheromones interact when they are in close proximity, causing them to have their period at the same time. Period timing is also known as “menstrual synchrony” and “the McClintock effect.” It is based on the theory that when you come into physical contact with another person who is menstruating, the pheromones influence each other so that the monthly cycles align.

Some women even swear that certain “alpha women” may be the determining factor when entire groups of women experience ovulation and menstruation. Anecdotally, menstruating people accept that period timing is a real thing that happens. But medical studies don’t have a strong case to show that it happens.

science doesn’t support it

In 2006, a study made the claim that “women do not synchronize their menstrual cycles”. This study collected data from 186 women who lived in groups in a dormitory in China. Any period of synchronization that seemed to occur, the study concluded, was within the realm of mathematical coincidence.

Another big study by the University of Oxford and period tracking app company Clue was the biggest blow yet to the period synchronization theory. Data from more than 1,500 people showed that women are unlikely to be able to disrupt each other’s menstrual cycles by being in close proximity to each other.

However, a smaller 2017 study keeps the idea of menstruation timing alive by noting that 44 percent of participants who lived with other women experienced period timing. Period symptoms, such as menstrual migraine, were also more common in women who lived together. This would indicate that women could influence each other’s periods beyond the time of their menstruation.

The most prevalent theory is that it is an evolved strategy among women to cooperate with each other, to stop becoming a kind of harem for a single dominant man. The idea is that if women had synchronized cycles, they would all be fertile at the same time, so a man could not reproduce with all of them. You can’t manipulate all the females at the same time, so it was believed to be a form of cooperation between females. However, it is only a hypothesis without scientific basis.

mujeres con menstruacion

Why can’t it be shown?

The truth is that we may never be able to determine how real the timing of menstruation phenomenon is, for a number of reasons.

Menstrual timing is controversial because we don’t know for sure if the pheromones on which the theory is based can influence when the period starts. Pheromones are chemical signals that we send to other humans around us. They signify attraction, fertility, and sexual arousal, among other things. But can one woman’s pheromones tell another that menstruation should take place? It is not known.

Timing is also difficult to prove due to the logistics of women’s menstrual cycles. Although the standard menstrual cycle lasts 28 days, beginning with 5 to 7 days of your “period” during which your uterus sheds and you experience bleeding, many people don’t experience periods that way.

Cycle lengths of up to 40 days are still within the realm of “normal.” Some women have shorter cycles with only two or three days of bleeding. That makes what we consider “period timing” a subjective metric that depends on how we define “timing”.

Menstrual synchrony may appear due to the laws of probability more than anything else. If we have periods for one week a month and live with three other women, it is likely that at least two have periods at the same time. This probability complicates research on the timing of menstruation.