What makes periods sync up

More Button Icon Circle with three vertical dots. It indicates a way to see more nav menu items inside the site menu by triggering the side menu to open and close. Kate Watson. Period syncing is the idea that women who spend a lot of time together will have their menstrual cycles align.

However, scientific studies have been unable to prove that period syncing actually occurs. Pure mathematical probability is the likeliest reason why women's periods sync up.

This article was medically reviewed by Olivia P. Visit Insider's Health Reference library for more advice. Kathryn Watson is a New York-based freelance journalist covering the intersections of health, relationships, and culture.

Her work has appeared in Allure, Vox, and Healthline, among others. Find more work on her website. In one older study from , over 28 percent of participants experienced period bleeding during the new moon phase. If this data set of women held for the entire population, it would indicate that 1 in 4 women have their period during the new moon phase. However, a more recent study conducted in suggested no connection. The truth is, we might never nail down how real the phenomenon of period syncing is, for a few reasons.

Pheromones are chemical signals that we send to the other humans around us. They signify attraction, fertility, and sexual arousal, among other things. But can the pheromones from one woman signal to another that menstruation should take place? Menstrual synchrony might often appear due to the laws of probability more than anything else. If you have your period for one week out of the month, and you live with three other women, odds are at least two of you will be having your period at the same time.

This probability complicates research into period syncing. A menstrual period is vaginal bleeding that occurs at the end of the monthly menstrual cycle. This is when the female body prepares itself for…. To submit your questions email us at questions sciencefocus. Manek has also developed teaching courses for Oxford Medical School, and has penned articles for The Guardian and Pulse magazine.

FYI, this pilot study hasn't been published anywhere but the app's blog so far. After receiving over 1, responses and narrowing it down to pairs of users whose cycles occurred at similar times, they tracked three consecutive cycles for each pair. Here are their most significant findings:. Side note: We're thrilled to catch a glimpse of all the possibilities that can come from opting into research with a period-tracking app.

As the Cleveland Clinic tells us, period syncing often comes down to a simple matter of time, rather than any kind of biological phenomenon. Hormonal birth control , stress , medications, health conditions, and disordered eating can all interrupt your usual cycle. While the study from the app team and Oxford doctor never moved past the "pilot" phase and into a peer-reviewed journal, the sample size was the largest compared to past studies.

If you're interested in moving fertility and reproductive health research forward, check out what we're working on at Modern Fertility and get in on the action. So, feel free to keep on knowingly nodding when friends or family members ask to borrow a tampon.

English Taylor is a San Francisco-based writer and birth doula.