General Question

rebbel's avatar

Have you heard of the phenomenon that girl friends' periods get synchronized when they are in each other's company (for a certain period of time)? [Details inside].

Asked by rebbel (23447 points ) February 3rd, 2012

To make it more clear: Say, Ellen used to have her period at around the fifteenth of the month and Gina around the twentyfifth of the month, but after a while, when they are in close company for a period of time (months?) their start dates will be the same (about).
My girlfriend has experienced this, with multiple girl friends.
Have you heard of this?
Is it a known phenomenon?
If so, what causes it?
Can males (partners or friends of the female) also get similar symptoms (belly ache) when her period is there?

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39 Answers

dappled_leaves's avatar

I’ve heard this before, but never actually experienced it. I suspect it may just be due to the fact that no one’s cycle is of exactly the same length… so eventually they must overlap. But do they stay overlapped? I would guess not.

digitalimpression's avatar

It certainly happens with females during deployments. Keep clear of the danger zone when it happens.

Earthgirl's avatar

I have experienced this with roommates and I’ve talked to other women who have experienced it too. It seems that the theory is not firmly established to be true. It may be caused by pheromones.

Coloma's avatar

I think it’s the herd factor, put enough females together for long enough and yes, it is true, we will synchronize our breeding cycles for maximum availability. lol

Personally I have always thought women should be like dogs, two seasons a year is more than enough. I wonder if women lived with Wolves, Jackyls and Hyenas if we’d take on the pack breeding cycles. haha

janbb's avatar

Have heard it but not verified it.

EverRose11's avatar

It is true

SavoirFaire's avatar

I’ve heard of it; and though I understand that menstrual synchrony is controversial, my wife has found that it happens among her and her close friends. This is significant because my wife is incredibly regular. Her period has never shifted from the expected schedule unless she was synchronizing with another woman with whom she was close. That is, she has never experienced an irregularity when it was not also the case that a close friend was experiencing an irregularity (such that their mutual irregularities were bringing their respective cycles into sync). What really convinced us was when it happened between her and another woman who was also incredibly regular as they became close.

jazmina88's avatar

yes, it has happened with me in the past.

fundevogel's avatar

I’m skeptical, primarily because I want to know who these women are that alert each other when they’re bleeding regularly enough to confirm such a thing.

SavoirFaire's avatar

@fundevogel Understandable. In my wife’s case, she got interested after first reading about the (putative) phenomenon. Our friends tend to be pretty open people, so she just asked the women among them about it outright.

Zaku's avatar

Yes, I have both read about it, and heard it confirmed by women.

I suppose some men might end up with some related symptoms, though I wouldn’t expect it to be due to the same mechanism. Certainly, sensitive men will feel an impact when the women they live with are suffering or changing moods, one way or another.

wilma's avatar

Yes it has happened in my family with my sisters.

I also took a trip with some women friends a few years ago. I was menstruating during that time. After we had been together for two days one of the women who was menopausal and hadn’t had a period in over a year started having a period. I had to loan her some tampons because she was so unprepared for it.
The day that we all returned to our homes (in different countries) one of the other women who had not had a period for over 3 years also began to menstruate. They all blamed me for having super pheromones or something. I have no idea if this was just some strange coincidence or if there was something else going on.

Keep_on_running's avatar

Judging by some of these stories it’s possible, but I don’t know if they’ve ever proven it scientifically. To me, it sounds like what @dappled_leaves said, inevitably this will occur.

[Removed by Fluther. No giving away state (award) secrets!]

RocketGuy's avatar

It happened to the women in my dorm.

Also, my wife is synchronized with her friend and her friend’s sister-in-law. They used to get together a lot. Now us husbands have each other for company when it’s danger time.

Sunny2's avatar

I’ve heard about it, but not experienced it. Does it happen with mothers and daughters?

JilltheTooth's avatar

I grew up in a family of women (and my rather tolerant Dad.) A mother and three daughters. We used to sync up all the time. I also went to a girls’ school, and although it wasn’t talked about much rather boring a topic necessary items for such times would be in short supply at regular times. It’s not hard to explain, as we all spew out different pheromones during different times in our cycles, so we all kind of know, because we can smell it.

troubleinharlem's avatar

Definitely! I live in a girl’s dorm right now and sometimes our half of the hall will all have their periods at the same time, so it’s kind of a disaster. Other times it’s just who we hang out with the most, like my friend is up on the third floor (I’m on the second) but we get ours at around the same time.

It has something to do with the “dominant uterus” (that’d be an interesting band name), who gets the periods to go around the same times. I believe that birth control keeps you from syncing up, but I don’t think that it’s proven yet. Here’s an article about the phenomenon, called the McClintock effect.

Also, @fundevogel, it depends on the women and their relationships with each other to see how open they are about their bodily functions. With my friends, at least, sometimes we’ll say something like, “Damnit, my ovaries are trying to kill me.” Then someone else might say, “Ugh, my period’s about to start in two days, I have to go get supplies.” So, it just depends on the woman and her relationships.

SavoirFaire's avatar

@troubleinharlem Good point. It would make sense that hormonal birth control methods would prevent it insofar as those work by overriding other hormonal tendencies. My wife uses an IUD, and one of her friends didn’t start synchronizing with her until she switched from the pill to an IUD.

BhacSsylan's avatar

I’m going to go against the grain, but no, it does not exist. The fact that so many people think it does has to do with the fact that cognitive bias is extremely common and many studies use retrospective surveys, which are very prone to such biases. Here is the critical review mentioned on wikipedia, which showed that when errors in previous studies were corrected for, the evidence disappeared: A critical review of menstrual synchrony research

From the abstract: “Three errors are inherent in research based on [McClintock’s] model: (1) an implicit assumption that differences between menses onsets of randomly paired subjects vary randomly over consecutive onsets, (2) an incorrect procedure for determining the initial onset absolute difference between subjects, and (3) exclusion of subjects or some onsets of subjects who do not have the number of onsets specified by the research design. All of these errors increase the probability of finding menstrual synchrony in a sample.Menstrual synchrony is not demonstrated in any of the experiments or studies.” Emphasis mine.

And from the conclusion (sadly behind a pay wall, though if any of you are very interested I may be able to send a copy): “The two experiments of Russell et al. (1980) and Preti et al. (1986) and the three studies of Graham and McGrew (1980), Quadagno et al. (1981), and McClintock (1969, 1971) all have two or three errors that bias their results toward showing higher than expected frequencies of menses onset convergence in their samples. I have demonstrated in all samples, except McClintock’s two samples of pairs, that statistically significant levels of menstrual synchrony are not found when these errors are corrected. A comparable demonstration for McClintock’s samples of pairs is not possible because the documentation of her research is insufficient for correcting errors and conducting revised tests for menstrual synchrony. ”
Emphasis mine.

Also, the phenomenon of human pheromones has never been shown to actually exist.

JilltheTooth's avatar

@BhacSsylan: Well, maybe your period has never synced up with anyone elses, but impressive post aside, I find it way beyond the realm of statistical probability that in 35 years of experiencing menses, that syncing would happen so many times to me personally. If my sisters and I had all been away at different schools, come Christmas vacation we would all sync up, and my mom, too, no matter where we were in our cycles. When I moved into a house with 4 other women, we were all synced within 3 weeks, again, we were all at different places in our cycles. Moving into a womens dorm in College (3 different dorms, 3 different times) a group of approximately 10 women in proximity all synced up within a few weeks. Not scientific, I know, but still valid. And when you cry “Anecdotal, doesn’t count” I respond with that raspberry noise that I can’t spell. Unless, of course, it’s just me, and I am that special.

BhacSsylan's avatar

I’ll pick just one anecdote of your’s to show why your thinking is flawed, @JilltheTooth: “a group of approximately 10 women in proximity all synced up within a few weeks.”

A menstrual cycle is usually 28 days. Four weeks. It’s impossible, assuming no woman in the has an exceptionally long cycle, to separate menstruation of two women for longer then two weeks. You could have been as far apart as possible, and still be “within a few weeks”. It’s called cognitive bias, and it happens to everyone. That is the entire point of doing studies that try to get around those biases.

Oh, and the issue isn’t just that your particular point of view is flawed (it could be, you could just be that special), but that cognitive biases can effect how we parse data. You remember those times that you ‘synced up’, but not the times that you didn’t. Or thinking that having a period on back-to-back weeks is ‘synced up’, when the chances of that happening are very high or any random two women, synced or not. Etc Etc Etc. Humans are pattern-seeking animals, and we’re quite good at making up patterns that don’t exist. Again, this is the point of studies, to try and discern what actually is real from what we think is real.

dappled_leaves's avatar

@BhacSsylan ^ Exactly. Thanks for the references; now I have more than just my suspicions to use the next time it comes up.

JilltheTooth's avatar

When I said “synced up within a few weeks” I meant it took only a few weeks for our start days to be the same, not that our cycles were within a few weeks of each other. We would actually be starting with 24 hours of each other. Those of us that were short cycled, like myself, (I would typically go 23–24 days,) would go longer, and the longer cycled women, (29–32 days), would shorten up, so we would have, after 2–3 cycles a mean of about 26–27 days. We would wonder what that did to our fertility probabilities, but we weren’t trying to get pregnant at any of those times, so that was never tested.

BhacSsylan's avatar

Okay, I misunderstood you then. You still have not explained how your anecdotes, a handful of experiences over 35 years, could not be subject to the cognitive biases we all experience. Or why your experiences trump the objective evidence I have provided.

Also, here is a more recent and non-paywalled review of the literature and issues surrounding it: Menstrual Synchrony: Do Girls Who Go Together Flow Together?

tl;dr: “I’ll summarize rather than trying to cover everything published on the subject. A Scientific American article did a good job of reviewing the literature as of 2007. Suffice it to say that about half the published papers support the synchronization hypothesis and half don’t; and the half that do have been harshly criticized for their poor design and poor statistical analyses. So we haven’t reached a consensus, but it’s looking more likely that synchronization is a myth.

Also, “The paucity of evidence for human pheromones suggests that if they do exist, their effects must be too small in magnitude to be very important.”

JilltheTooth's avatar

I only gave you a handful of examples out of many more. No trumping going on, just recounting personal experience. I told you it wasn’t scientific, I admitted it was anecdotal and that I knew you’d point to that. Knock yourself out with your links and stuff.

fundevogel's avatar

So you mean I don’t have some magical uterine bond with other women? Thank god. No offense ladies but you can keep your hypothetical pheromones to yourself.

BhacSsylan's avatar

@JilltheTooth Okay, but you were still arguing that it exists because of your experiences, thus that I (and my links) were wrong. My point was in showing that personal experience can be misleading. Again, we all have biases.

JilltheTooth's avatar

@BhacSsylan : It exists in my experience, it may not in yours, or for other women. There may need to be some kind of emotional connection, or a shared type of food or something, I don’t know, but I really have a hard time believing that a couple of studies will cover the whole of the female human experience. Some women sync, other women don’t, is that such a hard thing to believe? Because I wasn’t funded and published doesn’t make my intelligent and educated observation of my own environment less valid than others. By all means, don’t believe me, call my statements “cognitive bias” or whatever, I’m just answering kind of a light question on Fluther.

BhacSsylan's avatar

Is it so hard to believe that maybe, just maybe, you’re mistaken? At that the people who have sat down and studied this thing, who have actually looked at what may be causing it and tried to figure out if it’s really happening, might be right?

And yes, it is kind of a light question. But it is one that has actually been studied and looked in to, and so I gave the general scientific consensus. You’re the one who’s saying you know better then all of the intelligent and educated observations of the people I’ve linked to. If someone were to ask a medical question about her period, and a doctor come on to give a intelligent diagnosis (the problems with internet diagnosis aside) would you say your personal subjective experience is better?

Earthgirl's avatar

BhacSsylan Perhaps you should back off and let someone have their own opinion based on their own experience. No one really needs to prove anything. It is a phenomena that is not proven or disproven yet. The jury is still out.

NuGoonie23's avatar

I played basketball with the same girls for about two years. One day we had an away game and three of the girls started their period before our game.
It was indeed the weirdest phenomenon I had ever seen.

JilltheTooth's avatar

@BhacSsylan,:Oh dear, well I’m not going on further with this as I already allowed that my experience may well not be the same as all others.See my first sentence of my last post: ” It exists in my experience, it may not in yours, or for other women.” I’m sorry you are having such a hard time with this, in my life I have learned that following blindly the results of a few studies is not prudent. Remember in the 70s there was a definitive study that proved that the consumption of chocolate did not contribute to acne? It may well have been true, but it was funded by one of the major candy companies (I don’t remember who) and did not take into account any variables on production practices, other ingredients, etc. Just one example that I’m not going to waste my time trying to find a link to. I’m old enough to not be of the “If you can’t link it, I refuse to think it” generation.
And really, why is it so important to you to prove me wrong? Rhetorical, don’t answer that.

fundevogel's avatar

@JilltheTooth If he’s anything like me, this has nothing to do with the importance of establishing how the female uterus does or doesn’t behave and everything to do with your insistence that your experience constitutes a personal reality unbeholden to the scrutiny and discoveries made regarding the workings of the rest of the world.

I should like to know, if your reality is not subject to the rules and conditions observed, tested and found consistent in the world, what is the scope of your reality? Do you move through a separate world overlapping ours that only gives the appearance of interacting with our world or is it like a bubble of reality around you personally with it’s own rules and conditions that repels the conditions of other realities from applying to you?

I know this sounds snarky and I’m not trying to be mean, but what you’re saying sounds completely absurd to me and I would like to know how you think you or anyone else can have their own reality. It smacks of a question I asked earlier about people having their own “truth”.

SavoirFaire's avatar

@BhacSsylan You’ll notice that I acknowledged the controversial aspect of menstrual synchrony in my first response. It should be noted, however, that your responses operate on the appeal to ignorance fallacy. That the phenomenon is controversial does not prove that it does not exist, just as the anecdotal evidence given here does not prove that it does exist. But no one seems to be saying “it’s definitely real, my experience proves it.” A charitable reading commits us to nothing more than “here are some reasons in favor of the hypothesis.”

JilltheTooth's avatar

Oh, good grief, @fundevogel , I peppered my responses with a bunch of “this is my experience and it may not be yours” disclaimers, and I said that I don’t put absolute faith in miscellaneous studies that are linked on the internet and you get all up in my face about my “reality”? I’m not going to get into a ridiculous discussion with you about why you should or should not find my point of view “absurd”. To put it as gently as I can, this is not about that, you’re reading way too much into it, and I’m not going to engage because you don’t like how I express myself.

Response moderated (Flame-Bait)
fundevogel's avatar

@JilltheTooth So it’s not that you have your own reality. This is a matter of you believing your interpretation of your own experience over the findings of the studies @dappled_leaves provided? I misunderstood you.

JilltheTooth's avatar

@fundevogel : You certainly extrapolate a lot from my disclaimer filled posts where I said, for example, “It exists in my experience, it may not in yours, or for other women. There may need to be some kind of emotional connection, or a shared type of food or something, I don’t know, but I really have a hard time believing that a couple of studies will cover the whole of the female human experience. Some women sync, other women don’t, is that such a hard thing to believe?” and “I told you it wasn’t scientific, I admitted it was anecdotal and that I knew you’d point to that.” These are statements that qualify what I said. I read the links and I couldn’t find where any of them said that they covered the whole of the female human experience, or took into account every possible variable.
Would it not be more absurd to state that upon further reflection I have decided to deny decades of experience and observation in favor of the assertion of a stranger on the internet who has a couple of links, and the outrage of another stranger on the internet who believes in the absolutes stated by the first stranger?
And the answer to that would be: Yes, it would be more absurd. As would continuing with this ridiculous exchange.

fundevogel's avatar

@JilltheTooth I think you misunderstood my previous post. I wasn’t attacking you. I was acknowledging my fallacious understanding of your position and attempting confirm what your actual position was. I don’t know what there is to take offense to in this.

No extrapolation at all. Just trying to clear up my misunderstanding.

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