At some point in her life, every gal who lives with pals will experience this scenario:

“Does anyone have a tampon I can, um, borrow?” “Help yourself. I’m in the same zone babe.” “OMG so am I! We’re totally syncing!”

There’s a widely held belief that women who live together – or spend a lot of time together – begin menstruating on or around the same day each month. Some theorists go further and say that so-called ‘alpha females’ can hold sway over a group, effectively control their friends’ ovulation and period patterns.

And it has a name – two even: Menstrual Synchrony and the McClintock Effect.

McClintock, if you were wondering, is Martha K McClintock. As a researcher in the psych department at Harvard University in the US in 1970, she undertook a study of 135 students living together on campus at the nearby Wellesley College in Massachusetts. (She had graduated from there in 1969 alongside Hillary Rodham Clinton.)

Martha’s findings were published in Nature magazine in 1971, whereby she concluded that the women’s periods were, indeed, syncing up. She didn’t offer any concrete reasons as to why, but listed a number of possible causes including similar sleep patterns, shared stress issues and the effect of pheromones – the chemical signals that we send to the other people around us.

Fast forward 50 years and there’s a whole heap more data available to the scientific community, and more recent research does not support McClintock’s findings. In 2017, a team at Oxford University in the UK, with help from the period tracking and fertility app Clue, examined the data of more than 1,500 women and concluded that it was ‘unlikely’ that women were disrupting each other’s menstrual cycles, and that any perceived syncing was probably just down to the law of probability.

You do the math(s). If you have your period for one week of every month, and you live with three other females, chances are there will be some overlap, and two or more of you will be raiding the Juuni tampon supply at the same time.

But hey, we don’t want to debunk any of the mystery surrounding our harmony with wider cosmic rhythms, so we’ll just say, the jury’s still out.