Why does a womans menstrual cycle change when she is living with a group of women?

Studies have shown that groups of women living in close proximity gradually become synchronised with regards to their menstrual cycle.

This was first described in 1971 by researcher Martha McClintock, now with the University of Chicago, although it was more common knowledge long before then - for example in nunneries.

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.

A study of 135 residents of a women's college dorm confirmed the effect. Most of the cycle shifting occurred within the first four months and was usually complete after seven months.

The whole building didn't synchronize, just roommates and close friends although the women were unaware of what had happened. Later research has suggested that synchrony is caused by some sort of scent cue, or pheromone (an airborne hormone).

Scientists at the Sonoma State Hospital Brain Behavior Research Center in California identified several women who were believed to be "menstrual pacesetters" - they made other women conform to their cycles. The scientists placed cotton pads under the dominant women's arms for a day, and then wiped the pads on the upper lips of five female subjects three times a week. Within five months, four of the recipients were menstruating at the same time as their donors.

Interestingly, men also have an effect on women's menstrual cycles-and not just because they make women pregnant. Women who associate with males frequently find that their periods become shorter and more regular. One woman told McClintock that she had a six-month cycle length until she began hanging out with guys, at which point her periods began occurring every 4.5 weeks. When she resumed her solitary ways, her cycle lengthened again. Another round of cotton pad experiments, this time using males as donors, confirmed this. Having sex with a man at least once a week will also do the trick.

Why synchrony occurs is pretty much a total mystery. The only published theory treats it as an evolutionary holdover from prehistoric times, when it was common for men to take multiple mates and efficient reproduction was essential to the survival of the species. The author of this theory assumes that women in their brief monthly phase of peak fertility give off some pheromonic signal that drives men wild.

If his wives are on different cycles, hubby has a good chance of picking the wrong one when his nose tells him it's time to go into action, thus wasting precious bodily fluids. But if the women are all menstrually synchronized, he CAN'T pick wrong-they're all fertile. In short, synchronous menstruation compensates for congenital male cluelessness about women's bodies.

There is a little problem with this theory... surveys show sex occurs most frequently around the time of menstruation, when women are LEAST fertile!

Why Does Menstrual Cycle Change

This syncing up of your cycles is called the McClintock Syndrome.

Basically what happens is that every person emits pheremones, which are like a biological signal. Other people's bodies pick up on this and adjust. The menstural cycle is hormonal, and responds to the pheremonal signals of others.

This happened to me and my college roommates. We would all have our periods with in about a 10 day window of each other. What a happy home that was...ahaha.

If two or three women maintain close contact, eventually their periods with synchronize and come at the same relative times. B.

menstrual cycle changes when your stressed, undernourished, and any other emotional excitements and urges you feel.

being aware of your peers affect your moods, your emotions, your sensitiveness. maybe being with someone you know who can relate to you creates changes in you.

I wish someone would explain that one, too! I've noticed that myself! It's really weird!

i am looking for that answer myself my daughter got her period this year we have them one after other.

The crazy part, is that its true!!

But I sure wish that I knew why, if you find out PLEASE let me Know!!

that has NOTHING to do with it, the only time your menstrual cycle can change is when u travel why?i duno