Can women really transmit their period to each other?

The phenomenon of "menstrual synchronization" is no stranger to most female compatriots. Many people may have had the "personal experience" of synchronized menstruation between roommates, sisters, mothers and daughters, and even colleagues. Can women really transmit the disease to each other during menstruation?

Intimacy makes menstruation synchronized

In 1971, psychologist McClintock published his research in the famous scientific journal Nature, stating that women who live in the same room will have closer menstrual cycles. She selected 135 dormitory students at a women's university as research subjects and divided them into roommate group, close friend group, and random group. After six months of close contact, McClintock grouped and counted their menstrual days (the first day of menstruation) and found that the interval between menstrual days in the roommate group and the close friend group changed from 7-10 days to 3-7 days, and the cycles were becoming closer. The intervals between menstruation days in the randomized control group were 6-14 days and 5-15 days, respectively, which remained basically unchanged. Based on similar phenomena in other mammals, such as the "Whitten effect" in mice (pheromones released by male mice can synchronize the estrus periods of female mice), McClintock believes that pheromones are most likely the cause of this phenomenon.

This research result has sparked widespread discussion, and this phenomenon of menstrual cycles approaching each other is also known as the "Mc Clintock effect." In the following decades, many scientists have studied this phenomenon, and many of them have obtained results consistent with the "Mc Clintock effect." The research scope covers sisters, colleagues and even same-sex couples. The methods used in these studies are basically the same as what McClintock did back then, which is to count the differences in the dates of women's menstrual periods over a period of time.

Although many research results have shown the correctness of the "Mc Clintock Effect", some studies have also shown that there is no obvious menstrual synchronization phenomenon. In addition, the cause has not been confirmed for many years, the subsequent criticism of the research methods, and the unclear evolutionary significance have all cast doubt on the correctness of the "Mc Clintock Effect".

Question 1: What can I use to "smell" you?

Among the various studies on menstrual synchronization, we can easily capture a key word - pheromone, which is considered to be the main cause of the "Mc Clintock effect".

Pheromone is actually the transliteration of pheromone, also known as external hormone. In 1959, German biochemist Peter Karlson and Swiss entomologist Martin Luscher coined the term and defined it as "a substance secreted by one individual and received by other individuals of the same species, affecting their physiology or behavior."

There are many types of pheromones, the most well-known of which are sex pheromones. Many insects release sex pheromones to attract the opposite sex, and some orchids mimic the sex pheromones of female wasps to attract male wasps to pollinate them. Many studies currently believe that the recognition of sex pheromones is mainly related to the vomeronasal organ (VNO) rather than through the olfactory epithelium. Many mammals have a vomeronasal organ, such as elephants and mice, and their behavior has been shown to be affected by pheromones - but humans do not have a vomeronasal organ.

Thus, the magical pheromones are shrouded in mystery in front of humans. Although it is generally believed that human sweat glands (especially under the armpits) can secrete sexual pheromones such as androstenol and androstenol, whether we can actually receive such signals has long been a controversial topic. The complexity of human behavior and physiological systems makes research even more difficult.

To date, no pheromone has been clearly proven to have an effect on the human body. Such controversy makes the phenomenon of menstrual synchronization, which has long been speculated to be caused by pheromones, even more uncertain.

In 1998, McClintock published a study to prove that menstrual cycles are related to pheromones. She collected sweat extracts from the armpits of 9 women during the follicular phase (before ovulation) and luteal phase (after ovulation), and then smeared them on the upper lips of 20 women (I guess these 20 girls must have received a lot of subsidies to come...). Except for being asked not to wash their faces within 6 hours, the participants continued their lives as usual. The results showed that sweating during the follicular phase caused the participants to have their periods earlier, while sweating during the luteal phase caused their periods to be delayed. Combined with the fact that hormones in the body during the follicular phase promote ovulation while hormones in the body during the luteal phase inhibit ovulation, McClintock believes that this result proves that pheromones released at different times can affect the physiological conditions of others. However, this conclusion is a bit weak. The number of days of early and delayed menstruation (about 2 days) is a bit small, and is even similar to the fluctuation of menstrual period length - McClintock himself has to admit this.