The first time I heard about period syncing was when my mother, my sister and I were menstruating at the same time. To say the least that month was a rough month for my father, surrounded by 3 women with raging hormones. I told my friends about it, and one of my best friends pointed out that even the both of us menstruate at the same time in certain months. Since then I have attributed coincidence and probability to this phenomenon, but the internet says differently.
There is a large number of articles on menstrual syncing, and every other article has radically dissimilar opinions, facts (from their inferences), and beliefs. Everyone is entitled to their own opinions, but not their own facts.
Several studies conducted by prestigious universities and well studied individuals that point in completely different directions on menstrual synchrony.
Studies on Menstrual Synchrony
The earliest study carried out by Martha McClintock of Harvard University, in 1971, pointed out that period syncing is a scientifically probable occurrence. This study gave period syncing its name, the McClintock Effect. However since then there have only been more studies pointing to similar and different results. The McClintock study focused on a group of 135 college girls living in a dorm and studied their cycles for a year. Martha hypothesized that period syncing does occur when women are in close proximity to each other.
According to the study, “an Alpha female, or Alpha Uterus had a strong hormonal pull and that causes the other cycles around it to menstruate in unison. The pheromones in a woman's body are activated by triggers around her like, for instance when she sees her friend take a pad to the bathroom,”
However the latest studies conducted, after the advent of period tracking apps with more digital storage of information related to menstrual cycles, this hypothesis has been busted on several different occasions.
A 2006 study conducted by Zhengwei Yang, on 186 Chinese women living in dorms illustrates “...First, we collected data on menstrual cycles from 186 Chinese women living in dorms for over a year. We found that women living in groups did not synchronize their cycles. Second, we reviewed the first study reporting menstrual synchrony. We found that group synchrony in that study was at the level of chance. We then show that cycle variability produces convergences and subsequent divergences of cycle onsets and may explain perceptions of synchrony….”
Basically, they attribute a level of chance, or probability when it comes to period syncing, and explain it as a mere coincidence.
Another study conducted by the Oxford University in collaboration with the popular period tracking app Clue, using large volumes of data as their legitimising point. They received 1500 responses of which 360 pairs had semblance to period syncing, and from here Clue tracked 3 consecutive cycles.
They concluded, “273 pairs (76 percent of the sample) actually had a larger difference in cycle start dates at the end of the study than at the beginning of the study. Only 79 of the pairs behaved in the opposite way, with the gap between cycle start dates getting closer during the study. For all 360 pairs, the average difference at the beginning was 10 days, and 38 days at the end.”
I couldn’t read through their study due to some unresolved problem on their webpage but their study had been cited by several other articles due to the large volumes of data they have on menstrual cycles. They inferred that instead of syncing, cycles actually diverge, but, their study is the only proof of that.
In 2017 another study was conducted that supported the hypothesis of the original study in 1971.
The word menstruation comes from the root of Latin and Greek words meaning moon and month. Lunar cycles and fertility rhythms have been connected historically, and many still share this belief.
A study from 1986 inferred that over 28% of their population taken for study experienced period bleeding during big changes in moon phases like new moon or full moon phases. However this was later refuted in 2013.
What my Cycle Indicated
The days in red are the days I was on my period 2nd being the last day of my period and 31st being the first day of my period.The boxes highlighted in yellow are The Full-Moon Days. However since it ends and starts on the full moon day, instead of ending both times or starting both times, this could just be a coincidence. I say coincidence because most of the full moon days fall at the end or beginning of the month, and my cycle also falls at that time. Nevertheless, not everyone’s cycle falls at the same time as me. If this study were indeed true, it would mean that 1 in 4 women sync their cycles with the lunar cycle.
Why do the results radically diverge?
The radically different results could be attributed to the different data points taken for study. Lifestyle,general health and diet have a myriad different effects on the menstrual cycle. The original study studied American women, while the 2006 study studied Chinese women. Nonetheless the study conducted by Clue must have had many different data points but we cannot be sure of that fact because I cannot find or access their webpage.
Another reason is because pheromones have not been proven to affect menstrual cycles, they affect reproductive and sexual behaviour.
Moreover the menstrual cycle on average lasts for 28 days with bleeding lasting from 5-7 days. Even so, 40 day cycles and 2-3 days of bleeding are still within the realm of normalcy. For period syncing to exist it must be defined. Do we mean the syncing of the starting, ending or heaviest flow days? Till then, it will always be ascribed to the laws of probability and coincidence.
Sadly, due to the reasons I mentioned above, we may never find a clear answer to this contentious debate.
Written By: Triya Ghosh
Graphics By: Ananya Choudhury
Period Syncing: Real Phenomenon or Popular Myth? (Healthline)
Do women's cycles really sync? (Modern Fertility)
Women Do Not synchronize their periods: a study (2006 study)
Women living together have the same menstrual migraines (2017 study)
Menstrual Synchrony: The original study (1971 original study)
Moon Phases 2020 (Time and Date.com)
Clue: Period Tracking website (Hello Clue)