Facts of lifeSynchronous menstruation [Archives:2005/861/Health]

July 21 2005

By Dr. Khaled alNsour
For the Yemen Times

Did you ever know that women living together for a long time tend to have their menstruation around the same time? This is true; women and girls living together for extended periods have synchronized menstruation.

This amazing phenomenon was first described in 1971 by researcher Martha McClintock, now with the University of Chicago. Synchronous menstruation has been observed among mothers, sisters, and daughters who live together, and sometimes among women who simply work together. McClintock tells of seven female lifeguards who started out one summer with widely scattered periods. Three months later they were all menstruating within four days of one another.

Pheromone research

The odor sense is very important for insects. It is used for finding food, escaping enemies and finding a mate. Odors used to send messages between individuals of the same species are called pheromones.

The class of pheromones most widely explored are the sex pheromones in insects. In most cases it is produced by a female to attract a male of the same species. The first synthesised sex pheromone was bombykol, in 1959. It is used by the silk moth. Today the science know, in more or less detail, the pheromone of more than 400 moth species and a number of other organisms.

The reason behind synchronous menstruation is that women (and men) secrete odorless molecules, called 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.

Men have an effect too

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. This was observed among women who had lengthy cycles pre-marriage and once they got married their menstrual cycles became shorter and regular.