Girls living together will have the menstrual cycles synchronized?

“Do you have a tampon? I am running out of it.”, asking Jennie.  “Take it, I am taking a few with me today as I am also having a period”, Yumi said.

 

Have you ever heard of a myth that girls living or working together will have the menstrual cycle synchronized?  Do you share the same experience?  Is it because our hormonal discharge affecting one another?  Or our brain is responding to any invisible signals, resulting in the change of our physical situation?  Perhaps it is an adaptive feature of our human reproductive system?

 

In 1971, this phenomenon drew the interest of a psychologist, Dr. Martha McClintock, to study whether “menstrual synchrony” exist.  Forty years later, after different kinds of studies, scientists believe such phenomenal to be non-exist.  But this finding seems to be contrary to our experience, how come?

 

For illustration, assuming a cycle length of 28days, the maximum that two women can be out of phrase will be 14 days.  Taking more women into the pool of statistic, the average out of phase will down to 7 days.  Given the menstruation often last for 5 days, it explains why we are always under the impression that our menstruation is overlapping with each other.