Many women who live for a long time, study or work together, believe that their menstruation synchronizes and begin to occur at the same time. We decided to check how scientifically it is.

The fact that women spending a lot of time together are synchronized, monthly, many have no doubt. The options for synchronization of menstruation in Google fall: synchronization of menstruation with her sister, girlfriend, daughter or girl. Questions about this are asked on the forums, for example, on "Yandex.ku" or Quora, and in women's groups there are often jokes about this. Many Believethat synchronization is explained by female pheromones that interact with each other during menstruation. There is also a theory about Alfa Matka: supposedly one of the women in the team has a dominant uterus, which through pheromones sends another a signal for the beginning of menstruation. On the phenomenon of synchronization of menstruation even exists A separate article in the English -language Wikipedia.

Although in some traditional societies the myth of synchronization of menstruation in women existed, in modern media, it spread only in the 1970s. This happened thanks to the study of the American psychologist Marta McCinton, who studied pheromones.

In 1971, McCinton published in an authoritative scientific journal Nature The results of the study in which she studied the menstrual cycles of 135 women living in one of the American colleges. McCinton found that girls who have been living together for several months in a hostel or are friends closely, the difference between the first day of the menstrual cycle is reduced, that is, their periods are practically synchronized. The author of the study suggested that this is affected by the time that women spend together, since it allows pheromones to interact more tightly to each other.

Since then, scientists began to study in detail the synchronization of menstrual cycles in different groups of women: among colleagues, neighbors, in families and lesbian pairs. Studies were also conducted on other biological forms - for example, on rats or chimpanzees. Theories began to appear why this is happening. According to itself Popular Of these, the synchronization of menstruation could appear during evolution: supposedly if women in the menstrual cycles begin at the same time, then they are also sexually accessible at the same time. And this, theorists believed, leads to the fact that for women the risk of one man is minimized in the monopoly. If all menstruation will go at the same time, then everyone will have one time for fertilization. So, a man will not be able to have sex with all at once and women will be able to enter into sexual relations with different partners, thereby maintaining genetic diversity.

In the 1970s, on the wake of Feminism gaining popularity, such a theory looked attractive. However, later the researchers began to doubt not only in the theory explaining the phenomenon, but also in the phenomenon itself. Firstly, in the McClint methodology Noticed A few gross mistakes: for example, she conducted a study on women who had the initial difference between the first days of the cycle was given and the same. In addition, McCinton did not take into account the respondent with irregular menstrual cycles, although for an essential part of the population this may be the norm. (For example, in South Korea such women in 2019 it turned out more than 14%.)

But the most important thing: the author did not check and did not take into account the fact that the synchronization of menstruation can occur due to chance.

Taking into account the errors of the methodology, new studies did not give the same results as McCinton. In 2006, a large study with 186 women was done in China. Its authors discoveredthat most of the synchronizations could occur simply due to the non-equal probability of coincidence of random events, and could not confirm the phenomenon.

In 2017, an even larger study Spent At the University of Oxford using the Clue mobile application, which helps women track menstrual cycles, ovulation and plan pregnancy. The study was examined by about 1,500 respondents, all of them were divided into 360 well -known couples. Scientists did not reveal synchronization. Although this work did not go through the stage of blind review, most of the scientific community now He thinksthat the phenomenon of the synchronization of menstrual cycles needs serious scientific justification and is too well explained by a simple accident.

The fact is that women have menstrual cycles of different lengths, the same applies to the period of menstruation itself. Because of this, at some point, the girls discover that their menstruation came closer, but after that, the menstruation will be filled again (and converge again later). Noting only periods of coincidences, women think that their menstruation coincides due to the fact that they spend a lot of time together.

This is how the scheme of random coincidence of menstruation looks like women.