When it comes to their periods, many women feel a sense of interconnectedness with other women. It’s possible you’ve felt it, too: maybe after a stranger has handed you a much-needed tampon in a public restroom, or when you’ve realized your bestie’s cycle is synced with yours. But that connection may also feel bigger. For centuries women have felt a link between their bodies and nature — with the changing of the seasons or with the waxing and waning moon. Is it all myth and lore? Perhaps. But some studies may surprise you.
Is there a connection between your period and the moon cycle?
For centuries people have believed that a link exists between lunar and menstrual cycles, largely because of the similar cycle lengths. A lunar month — the length of time between two new moons — has a mean period of 29.5 days.1 And while most women’s menstrual cycles range from 23 to 35 days, many believe the average cycle length is 28 days, which is almost identical to that of the moon.
The ancient Greek philosopher Aristotle believed that menstruation took place during the waning moon.2 And even though French physician J. A. Murat reported in 1806 that the menstrual cycle is not governed by the lunar cycle,3 the idea has resurfaced time and again.
Charles Darwin alluded to it in his book “The Descent of Man, and Selection in Relation to Sex” (1871),4 though later studies refuted the concept. Nearly 100 years later, in the 1980s, the idea burgeoned again with several studies claiming “a synchronous relationship between the menstrual cycle and lunar rhythm.”5,6
In January 2021, a popular study of 22 women over the course of 32 years showed that women with menstrual cycles longer than 27 days were “intermittently synchronous with the moon’s luminance and/or gravimetric cycles.”7 The study hypothesized that “in ancient times, human reproductive behavior was synchronous with the moon,” but “our modern lifestyles have changed reproductive physiology and behavior.”7
However, three months later, a March 2021 study using menstrual cycle onset data from 529 women showed no association between menstrual cycle onset and lunar phase.8 And in 2019, a study conducted by the period tracking app Clue analyzed 7.5 million cycles from 1.5 million users and confirmed that women’s menstrual cycles don’t sync with the lunar cycle.9
Do menstrual cycles change with the seasons?
Few studies show correlation between menstrual cycles and the seasons. However, sunshine can affect the length of your cycle. One study demonstrated a trend toward a higher frequency of ovulation (97% vs. 71%) and a shorter menstrual cycle (by 0.9 days) in summer vs. winter.10
Is period syncing real?
Period syncing, also called the “McClintock effect,” is a phenomenon named after a 1971 study published by Martha K. McClintock in Nature. McClintock studied the menstrual cycles of 135 Wellesley College women and determined that the onset date of menstruation was more similar among those living together, as well as close friends.11
Several more experiments and studies supported McClintock’s claims, but then came the rebuttals. Four studies failed to replicate the results, and in 1992 a comparison of all the studies and experiments stated that menstrual synchrony was not demonstrated at all.12 Similarly, in 2006, a study of 18 pairs and 21 triples of college-age women over a five-month period also found “no conclusive evidence” for the existence of menstrual synchrony.13
While studies and debates continue, one thing is certain: Misconceptions and mistruths about menstrual cycles have long permeated cultures and societies around the globe. Thankfully, more women have access to accurate information about their reproductive health than ever before. Current education, research, clinical studies and technological developments are transforming the way we manage it — and better understand it.
- “Lengths of Lunar Months 2021,” EarthSky, (Jan 1, 2021), https://earthsky.org/astronomy-essentials/definition-what-are-lunar-months/.
- Dean-Jones, L., (1989), “Menstrual Bleeding according to the Hippocratics and Aristotle,” Transactions of the American Philological Association (1974-), 119, 177-191, https://doi.org/10.2307/284268.
- Bj√∂rn Lemmer, (2019), “No correlation between lunar and menstrual cycle – an early report by the French physician J. A. Murat in 1806-,” Chronobiology International, 36:5, 587-590, https://www.tandfonline.com/doi/abs/10.1080/07420528.2019.1583669?journalCode=icbi20.
- Darwin, Charles, “The Descent of Man, and Selection in Relation to Sex,” (1871), D. Appleton and Company, New York.
- Law S. P., (1986), “The regulation of menstrual cycle and its relationship to the moon,” Acta obstetricia et gynecologica Scandinavica, 65(1), 45-48, https://doi.org/10.3109/00016348609158228.
- Cutler, W. B., Schleidt, W. M., Friedmann, E., Preti, G., & Stine, R., (1987), “Lunar Influences on the Reproductive Cycle in Women,” Human Biology, 59(6), 959-972, http://www.jstor.org/stable/41463960.
- Helfrich-Förster C, et al., (2021), “Women temporarily synchronize their menstrual cycles with the luminance and gravimetric cycles of the Moon,” advances.sciencemag.org/content/7/5/eabe1358.
- Komada, Y., Sato, M., Ikeda, Y., Kami, A., Masuda, C., & Shibata, S., (2021), “The Relationship between the Lunar Phase, Menstrual Cycle Onset and Subjective Sleep Quality among Women of Reproductive Age,” International Journal of Environmental Research and Public Health, 18(6), 3245, https://doi.org/10.3390/ijerph18063245.
- Science Team at Clue, (2019), “The myth of moon phases and menstruation,” helloclue.com/articles/cycle-a-z/myth-moon-phases-menstruation.
- Danilenko, K. V., Sergeeva, O. Y., & Verevkin, E. G., (2011), “Menstrual cycles are influenced by sunshine,” Gynecological Endocrinology: The Official Journal of the International Society of Gynecological Endocrinology, 27(9), 711–716, https://doi.org/10.3109/09513590.2010.521266.
- McClintock, M., (1971), “Menstrual Synchrony and Suppression,” Nature, 229, 244–245, https://doi.org/10.1038/229244a0.
- H. Clyde Wilson, (1992), “A critical review of menstrual synchrony research,” Psychoneuroendocrinology, 17(6), 1992, 565-591, https://doi.org/10.1016/0306-4530(92)90016-Z.
- Ziomkiewicz, A., (2006), “Menstrual synchrony: Fact or artifact?” Human Nature, 17, 419–432, https://doi.org/10.1007/s12110-006-1004-0.
- Merriam-Webster, (n.d.)., “Hysteria,” In Merriam-Webster.com dictionary, retrieved November 11, 2021 from https://www.merriam-webster.com/dictionary/hysteria.