Menstrual health has long been overlooked by the scientific research community, and there are many myths, theories, beliefs and social stigmas which lack conclusive evidence. One of these is the idea of cycles lining up, or "syncing."
After our research partner Dr. Alexandra Alvergne from the University of Oxford wrote about the history of the cycle syncing theory, we asked Clue users if they thought their cycles had been syncing with another person (who also uses Clue).
Over 1,500 people replied, and told us what type of relationship they're in (friends, siblings, parent/child, partners, roommates or colleagues), if they live together and if they're on hormonal birth control.
From our small pilot study of Clue users, our data scientists found that cycles between pairs and cohabiting individuals did not align. Our statistical evidence also indicated that cycles are actually more likely to diverge, rather than sync, over time.
It's common for cycle lengths to vary, and periods usually last for several days, so it's likely that you will sometimes get your period at the same time as your friend, partner or sibling. This can give the false impression of synchronicity, and could be the reason why many people report their period syncing with others at some point in their lives.
How do you feel about our research results?
What if you get your period and you are also dating someone with a period, and you live together? Is it more likely that you will sync? We asked cohabiting lesbian, queer and trans couples about their experiences. Here's what they had to say:
"I think your findings make sense. Much is made of the idea of people with menstrual cycles 'syncing up' and it seems like often it's used as yet another way to dismiss (mainly) women when they are menstruating. In the context of romantic/sexual relationships between two people with menstrual cycles, it is used as a way to criticize our relationships, implying that it must be explosive and intense at all times in our house because two 'crazy and hormonal' people are around each other all the time.
My partner and I don't experience many adverse effects of menstruating, and we find that we have times when we have our period at the same time, but usually we don't. We're both slightly irregular, we think probably due to not needing or using contraception, so it makes sense that after several months of not being the same we would be the same for a bit. There are only so many days in a month so it makes sense that sometimes you will have the same days as the people around you!" - Hannah
"I didn't sync [with anyone] because I'm on the pill to regulate my cycle." - Anonymous
"We sync in odd ways. My cycle is very short but regular. Hers is regular but longer. She will have a few periods every year that are a week or more early — syncing with mine." - Anonymous
"We have never synced. The one time we started our period on the same day both or our cycles changed length and after that we have never been in sync again. I have only heard anecdotal evidence of friends who have seemingly synced with their sisters, but I did find it slightly surprising that there was no evidence at all in your study for synchronization." - Eloise
"I am completely synced with my partner, it's scary." - Anonymous
"I've long heard that cycles sync. I've experienced times where non-partner female people and I have synced up, but the syncing doesn't seem to endure. My partner and I have not synced but she uses a copper IUD and has a very established menstrual pattern and I am advanced in perimenopause and my cycles are not as regular as they used to be. So, I suspect 'syncing' is really a confluence of different cycles intersecting at a given time." - Anonymous
Why does this idea of menstrual synchrony persist?
Do we want to believe in it? If we sync our cycle with someone, does that mean we have a special connection? Or are we interested in cycle syncing for more practical reasons?
"After reading about your research, I suspect that one reason why some people are so into the idea of syncing is due to a need for bonding — menstruation is still so taboo in society that it's nice to be able to bond with other menstruators over something. Plus the idea of women mysteriously syncing up adds to this whole thing of 'we'll never fully understand the mysteries of the female body' which has its roots in misogyny.
I also think many people in relationships where both people menstruate are frustrated by being uncomfortable being sexual with their partner while one or both are menstruating, and so if people can cling to the idea that syncing is possible, it might make them less worried about a lack of sex for half the month, and hope instead for only a quarter of the month. Even though it is perhaps not based in science." - Hannah
Going forward, we may conduct a more comprehensive follow-up study. Perhaps a longer time-frame would provide different results.
"Yes, I have synced after 16 years" - Anonymous
We'd like to continue to do more analysis on this topic, and others in the under-researched field of menstrual and reproductive health. Do you have ideas about what we should study? Are you a scientist who would like to collaborate with Clue? Write to us at firstname.lastname@example.org
Want to know if you're in sync with a partner or friend? Track your cycle with Clue to find out.