Women’s cycles will often sync when they work or live close together.
Women’s periods correspond with phases of the moon, according to anecdote.
Both are true.
It’s called the menstrual synchrony phenomenon:
Menstrual synchrony is a phenomenon in which menstrual cycle onsets (i.e., the onset of menstruation or menses) become closer together in time than they were at an earlier time. “For example, the distribution of onsets of seven female lifeguards was scattered at the beginning of the summer, but after 3 months spent together the onset of all seven cycles fell within a 4 day period.” This phenomenon is hypothesized to occur when women live together, are related, or are close friends. Martha McClintockpublished the first study reporting the phenomenon of menstrual synchrony (sometimes referred to as the McClintock Effect) among women living together in dormitories. The term synchrony has been argued to be misleading because no study has ever found that menstrual cycles become strictly concordant, nevertheless menstrual synchrony is used to refer the phenomenon of menstrual cycle onsets becoming closer to each other over time.
Menstrual cycle synchronization is the process by which the menstrual cycle onsets of two women or more women become closer together in time than they were several months earlier.
Cutler and Law hypothesized that menstrual synchrony is caused by menstrual cycles synchronizing with lunar phases. However, neither of them agree on what phase of the lunar cycle menstrual cycles synchronize with. Cutler hypothesizes the synchronize with the full moon and Law with the new moon.According to our recent poll, 99% of women menstruated on the new moon in their last menstrual cycle. That’s 412 women out of the 423 women who participated in the poll. Looks like many of us are synchronizing our menstrual cycle with the moon cycle after all.
You’ve probably heard that in ancient times women menstruated together on the new moon and ovulated on the full moon. I’m delighted to know that the powerful connection between the moon cycle and the menstrual cycle is still very strong today.