It's a common belief that women who live together or who are very close can get to synchronize their menstrual cycles, is it really true? There are several studies that allow us to reach a conclusion.
A study conducted in 1971, on university students, reported this phenomenon, and affirmed that most of them believed that their cycle was synchronized and that it was something pleasant.
As a result of this first study, many more were developed, but they suffer from serious methodological errors, which makes the subject treated scientifically controversial, and what seems to happen is that the variations of the cycle make women believe that synchronization could occur between them.
To demonstrate this, in 2006, two scientists collected information from 29 groups of women who lived in the same dormitories at a university in China, for more than a year. In each room there were between 4 and 8 women, which would be ideal in terms of the conditions for the synchronization of the cycle, if pheromones were the mechanism of the same (pheromone is understood as the substance produced by a living being and that can modify the behavior of another living being, this can be transmitted through the air or by direct contact).
While the university had vacations twice a year, most of the students remained on campus. A total of 186 women participated. Some of them began to coexist a couple of years before others, but the information began to be taken at the same time. The age of the students varied between 17 and 23 years.
They were given to each one a notebook where they were asked to record the beginning of their menstruation date, which was collected every 1 or 2 weeks; the data recorded during the holiday period were requested on the first day of the start of the new semester.
Through different methods of mathematical analysis, it was concluded that the level of synchronization reported in the first study of 1971 was due to chance.
Due to the variability of the cycle itself, in certain women it was seen that for example on day 250 of the study, their cycle synchronized for at least two consecutive periods, and subsequently these diverged.
The scientists also analyzed previous studies and observed that in 1980 it had been reported in different groups of animals, such as rats, hamsters and monkeys, synchronization in heat, but also showed that these facts were due to pure chance.
Therefore, the given synchronization was the result of chance, because each woman can suffer alterations in her menstrual cycle that have nothing to do with whether her congeners are menstruating.
The normal menstrual cycle varies between 21 and 35 days, with two to six days of blood flow and an average blood loss of 20 to 60 ml, considering the menstrual cycles of each woman are variable, it is normal that casually a coincidence occurs in menstruation, but it has nothing to do with coexistence.
Leaving the theory of pheromones aside, situations of stress and anxiety generated in a workplace, study or at home can disturb the menstrual cycle and therefore the periods of different women may coincide, but it is still a merely casual coincidence.