Study suggests menstrual-cycle syncing by women does not really happen

April 19, 2017 by Bob Yirka report
Credit: Clue blog

(Medical Xpress)—A team of researchers made up of the group behind the fertility app Clue and a group at Oxford University have tested the popularly held notion that when women live or work in close proximity for a span of time, they find their menstrual cycles begin to sync with one another. But as researchers note in their article on the Clue website, such notions appear to be completely false.

It is a commonly held notion that who live or work together, or just spend a lot of time together, find their syncing. There was even a study done in 1971 by Harvard researcher Martha McClintock tracking the menstrual cycles of female colleges students sharing a dorm. But, as the researchers with this new effort note, no other studies have found it to be true, and McClintock's work has been discredited. But sill the myth persists. To perhaps put an end to the debate, the researchers conducted a test trial with women who use the Clue app—1500 women responded to their request for assistance in a trial and out of those, 360 pairs of women were selected for inclusion. Each were in a close relationship with another woman over an extended period of time. Because the app helps women track and share their period information, the data was already available; all that was needed was for the users to share it with the researchers.

The researchers looked back three menstrual cycles for each of the pairs to see if any alignment was occurring and report that 273 of them actually had cycles that diverged—just 79 were seen to converge. They note that women who were living together were no more aligned than the other pairs. This, they insist, is further proof that the entire idea is a myth with no basis in reality.

Regarding why so many women believe the myth, the researchers suggest it has to do with chance and emotion—cycles last on average 28 days, which means a pair could, at most, be out of sync just 14 days. Simple math shows they would be out of sync on average just seven days, which could lead to a misperception of syncing, especially considering that the is so prevalent.

Explore further: Demystifying menstrual synchrony—women's subjective beliefs about bleeding in tandem with other women

Related Stories

Cinnamon may improve menstrual cyclicity in PCOS

October 31, 2014

(HealthDay)—For women with polycystic ovary syndrome (PCOS), cinnamon supplements may improve menstrual cyclicity, according to a study published in the November issue of the American Journal of Obstetrics & Gynecology.

Early and late menopause can increase risk of type 2 diabetes

July 27, 2016

Women who begin menopause before age 45 or after 55 have an increased risk of developing type 2 diabetes, according to a study of more than 124,000 women enrolled in the Women's Health Initiative, a large national trial aimed ...

Recommended for you

Technique for 'three-parent baby' revealed

April 3, 2017

Details of a pioneering IVF technique using mitochondrial replacement therapy (MRT) have been revealed, giving hope to those families with inheritable mitochondrial disorders that they may be able to have healthy children ...

Technology to screen embryos before implantation falls short

March 31, 2017

The healthy development of an embryo created through in vitro fertilization (IVF) depends on whether most, if not all, of the cells have the proper number of chromosomes. With pre-implantation genetic screening (PGS) technology, ...


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Apr 19, 2017
Among other things, the unethical practice of declaring the assertion a "myth" simply because one study was "discredited". Even if a study is "discredited", the assertion can still be true! And note the odd description of "perhaps putting an end to the debate". Isn't that described as an aim of "science"?
And note the structure of the "experiment". Among other things, using only those who used the app. That is not established as as random or wide ranging as needed! They chose pairs of women who, it seems, were in close contact with each other for some time. Then they look at only the past three months of their periods. Why so short a time? Too, there is absolutely no attempt made, it appears, to verify that the women did not have even closer contact with other women, women who didn't use the app! And, face it, if, in the vast majority of cases, the periods diverged, that doesn't mean nothing's happening! Something seems to be acting!
1 / 5 (2) Apr 19, 2017
finally was able to conceive a child to my own the year 2016 after 21 years without any issue. thi s really was the worst thing ever. It was a miracle that indeed shocked me. because i was left with no option but to use a Herbal Health Concoction that was prepared from Herbs to help the Immune. I got to find out about this from someone and i talked to the direct source about my problem. He`s name is Dwr Dexter and HE told me how some necessary few herbs will be useful as to women`s health and recovery and he had to do what knows best. He sent the Herbs to me and gave instruction on method of use. this all happened and i really have been able to say i`m glad God did this.
You can congratulate me (469) 573-2540 or mail me
but don't call at bed time..
You can get in-touch with Dexter via Email (
Really just felt like dropping this, not for all Tho.Dwight dexter
5 / 5 (1) Apr 19, 2017
No, there is no aim of science in perpetuating debates about assertions that have been proven false. And no, when there's only one study supporting an assertion that is subsequently only disproved by followup studies, that is when the assertion has been proved false, and the supporting study discredited. That in fact is precisely the entire aim of science: to disprove assertions, proving them false; to discredit support for those false assertion; to end unscientific and wasteful debates that are nothing but fallacy.


Among other things
5 / 5 (1) Apr 19, 2017

According to the 1971 McClintock study, the 1500 women in the 2017 Clue study should have showed far more women with converging cycle timing than diverging, but the opposite was true, almost 3.5:1 - to say nothing of the over 3/4 of women whose timing wasn't correlated at all.

For there to be selection bias, as you imply with your complaints about methodology, unusual menstrual cycle immunity would have to correlate with responsiveness to recruitment for the study. There is no evidence of that complex implied relationship.

This study should be repeated, since 1500 women aren't enough to be certain about over 3 billion of them alive today. But its results are clear enough that only science trolls who don't understand science, probably because science threatens their own favorite myths, would think anything but that it shows debating "menstrual cycle syncing" is at best to be resolved by those other studies.

Among other things
not rated yet Apr 19, 2017
Often skin surface microflora process human secretions into human pheromones. Kill the microflora, diminish the pheromone emitted. Alter the microflora, change the pheromone. Hygiene practices have changed since 1971. Hugs & handshakes, victory celebrations, arm in arm, all share microflora. Lacrimation enhances pheromone reception.
The trouble w/ human pheromones is that collecting them & playing around with them leads researchers themselves into difficulties. For instance, take facial skin surface lipids of an adult man. Collect 300 mgs of his "face grease" & the undetectable-to-humans stench from the collected sample becomes evident, an airborne plume of pheromone released by the collected skin surface lipid plays havoc w/ research teams without training in handling potent airborne poisons. Collaborations involving human pheromones suffer distrust, suspicion, astonishment/stupidity, arrogance, & always jealousy (where kissing partners detect saliva concentration changes).

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.