Is there a scientific explanation for why women who are close have their period at the same time?

Question

When it comes to menstruation my housemate and I are both very irregular, yet we seem to be in sync with each other! This month we started at almost the exact time and day, despite being about 50 kilometres apart at the time, and then irregularly started again 2 weeks later, at roughly the same time

Answer 1

Social regulation of ovulation, of which the most common form is menstrual synchronicity, has been observed in women living together. It has been found in room-mates, close friends, lesbian couples and most strongly between mothers and daughters. It has also been noted in mice, hamsters and rats, as well as prosimian primates such as the ring-tailed lemur.

The pioneer in this field of research is Martha McClintock of the Department of Psychology at the University of Chicago. She first reported her observation in Nature in 1971 and it has come to be known as the McClintock effect. It is believed that chemosensory signalling involving at least two pheromones and the vomeronasal organ (VNO), also known as Jacobson's organ, is responsible for the effect.

Check out this http://www.newscientist.com/backpage.ns?id=lw892 for the rest of the story.

Answer 2

Although the exact mechanism is still unclear, it is widely suspected that this occurs due to odorless molecules called pheromones. Women (and men) secrete pheromones in a manner as common as sweating. In fact, the sweat of many mammals contains pheromone chemicals. The molecules from one woman bounce and jiggle their way airborne and waft to another. Receptors in the nose detect the pheromones and the second woman responds by shortening or lengthening her menstrual period. Gradually, over the course of a few months, the periods of all the women living together synchronize in this way.

A study (that determined all this by Martha McClintock and Kathleen Stern) indicates the sweat probably contains two chemicals: one that lengthens menstrual cycles and one that shortens them. The two substances can act together to synchronize the cycles and sometimes to disrupt them.

By the way, similar studies show that men's pheromones also affect women's menstrual periods. Women respond to these pheromones by shortening their periods and having them more regularly.
http://www.answerbag.com/q_view.php/20649

Answer 3

Studies suy it is ptheramones. It is a proven fact.
That is why really smart guys keep their girlfriends with separate apartments from their wives. Both of them having pms at the same time is not good.(:-)-<-<

Answer 4

I´m tired of people who says your questions are stupid and still they are getting points for that. I don´t know why that happens but it happens to me and my mom too.