The first paper published in 1971 showed menstrual synchrony existed. This paper showed when women spend more than 3 months together their periods will start within 4 days of each other’s. This study has not been duplicated through controlled medical studies to support that this actually is a real phenomenon. It could be an old wive’s tale but even with those there is some notion of truth.
What I have learned during the 25 years I have been a physician is not everything that happens to us medically can be proven through scientific research. —Dr. Sherry Ross
Although we have not been able to measure pheromones and the existence of them is unproven, there is little doubt they exist. Pheromones are considered to be airborne chemical signaling molecules that are released by humans, animals, and plants into the environment and they can affect the physiology and or behavior of other members of the same species.
In particular, the research on the phenomenon of menstrual synchrony was shown to be robust in for mothers and daughters as well as roommates.
I think it may be difficult to draw conclusions from studies because there are factors that cannot be measured that play a role in menstrual synchrony such as the particular nature of the relationship and the specific living arrangements of the women. —Dr. Prudence Hall
I do think the strongest piece of the [McClintock] study is that women's cycles can be affected by lunar phases in the same location in the same way and that if they are sleeping and rising at the same time, therefore exposed to the same light/dark exposure, that those two things can create synchrony via the pineal gland, which consequently moderates melatonin's effect on ovulation patterns. —Alisa Vitti
One theory I’ve heard is that it’s not the women’s pheromones that they’re responding to… but the pheromones of a nearby male. And if they all are in close proximity to the same male, perhaps that would cause them to sync to each other. Interesting theory. Kind of annoying to me - I’d rather us women sync up with each other than have some man dictating us all :) But I haven’t seen any studies to confirm this theory either. —Katherine Altneu, acupuncturist, herbalist and fertility specialist
I have studied ancient women's rituals. Women used to coexist and live together in ways that we don't today. In those times it was incredibly common for women to retreat to what they would call the "Red Tent." This ritualistic retreat was a sacred way to honor the menstrual cycle. —Paula Mallis
I was chatting with my business partner at Carriage House Birth and she shared that when she took her doula training (all women) they all seemed to sync up. The instructor of the training had gone without a moon for many years and miraculously started menstruating with the group. Amazing right? —Lindsey Bliss
Not only do I have my own personal experience and those of the women I work with in my practice, but there are historical accounts of menstrual synchrony as well. In many ancient cultures around the world there is evidence of women gathering together during their periods, and suggestions that they were actually synchronized to the alpha-woman of their tribe. Whilst the book itself is a work of fiction, The Red Tent by Anita Diamant gives a glimpse into what these gatherings may have looked like. Menstrual synchrony has also been a way of regulating social and sexual life, as found in the Suri people of Ethiopia: between culture and biology. —Jodie Milton