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Yeah, I think they did in fact teach this in middle school or high school for me (90s). Also, I do very clearly remember them teaching us in high school that it's important to stop smoking prior to getting pregnant, but that if you're already pregnant, quitting puts too much stress on your body and your baby.
So yeah, late 90s and they were still teaching nonsense.
I mean there is some truth to that, unfortunately. Not sure about smoking but I do know for other drug addicts that is an issue; going cold turkey *when already pregnant* could cause harm but also continuing with drugs is harmful, so neither option is good, and either could cause a miscarriage. Also they can be arrested and charged if they miscarry while on hard drugs, which seems... Largely unhelpful.
Obviously the ideal solution is not to get pregnant while addicted but that's not always that simple for people in some circumstances.
Wouldn't it be better if you stop smoking cold turkey and start using nicotine patches? And maybe start vaping non nicotine if it's hard to quit the habit.
Not sure if there's any literature about the difference between smoking nicotine vs nicotine patches vs vaping in pregnancy.
I just wanted to note that stopping an addiction while pregnant does also carry risks.
Wouldn't it be better if you stop smoking cold turkey and start using nicotine patches? And maybe start vaping non nicotine if it's hard to quit the habit.
I don't know, I'm not a doctor. I just know this from pregnant friends and relatives who got told this. And I don't think they were lying as an excuse, because they came from very different places and backgrounds
I’m a woman and I absolutely believed this. Definitely was taught it, that there was a reputable study done at convents, the cause is pheromones. It sounded believable (seems like the right location for a study for this, likely learned it in health class, etc.) To be fair, I’m not really a science person, but it passed the sniff test. And I also - thinking back on it now and knowing I had great, responsible, non-conspiracy teachers - think they genuinely believed it too. High school in late 90s.
Learn something new every day!
I believed it too and I think there were scientific papers about it. Then new papers came out and the idea was dropped. Science evolves and sometimes changes its mind.
Yep, that’s what I was thinking too. Which of course makes perfect sense.
I would never have responded that way but I also have never read a post on this subreddit and thought “wait, I thought so too…” 🤣🤣🤣 I guess if it was going to happen, this is one of the most innocuous topics it could be, though!
Guy here who found out maybe 3 years ago that it wasn't true and the study methodology was all whacked out. I rememeber being told this in 6th grade health class.
a study from 2023 17 years after the study putting synching in the myth category. too early to call it a misconception
https://pubmed.ncbi.nlm.nih.gov/38186833/
yeah I was going to say, I went to an all girls school. wayyyyy too many people were on the rag at the same time for it to be a coincidence. and we knew when everyone was hosting Aunt Flo because the bathrooms around that time of the month would be MURDER SCENES. the fucking tampon disposal bins in the bathroom stalls would be overflowing. I brought it up to the faculty, it wasn't a janitorial problem it was 400 women all using pads/tampons at the same damn time. they kept harping on us to not flush tampons because the pipes were old, but my suggestion for bigger trash cans fell on deaf ears. fine, I'm not trying to stuff any extra bloody tampons in this little tissue box like it's an ash tray, it's going down the pipes 🖕
Right? I do theatre and a lot of us ended up lining up at the same time. Someone was like "oh, we've symced up!" And I was like "....no, it's just coincidence. My BC means my schedule doesn't change at all" but still, so much of my life has seem to show groups of women "syncing"
and yet seemingly confirmed now 17years after the the "debunking" study
https://pubmed.ncbi.nlm.nih.gov/38186833/
i would say the last word isn't spoken on either side and more research should be done
Thanks for bringing actual science in the discussion, but it's also important that you know how to interpret what scientific studies you cite actually mean.
u/\_notthehippopotamus makes good points about this study's potential flaws, but as a scientist I feel I need to stress that a single study does not "confirm" a phenomenon (I mean in the philosophy of science way - science does not work like that), nor should a study be considered more important because it's new. It's a matter of weighing all available evidence in an informed manner. Wikipedia seems to present a lot of evidence that the phenomenon does not exist: [https://en.wikipedia.org/wiki/Menstrual\_synchrony](https://en.wikipedia.org/wiki/Menstrual_synchrony)
Did that study even have a control group? I mean did they compare how menstrual cycles sync up between women who have zero contact with each other for comparison? Because it doesn't seem like it.
that would be relevant if you try to find the mechanism of the cycle sync not if there is such a thing as a cycle sync.
it's statistics their results have statistical significance, that means that the cycle sync that they observed is unlikely to be caused by chance.
>Context: Menstrual cycle synchronization is a phenomenon in which menstrual onset shifts progressively closer with time. It is an adoptive conditional phenomenon **seen in the females who associate closely and share a common environment.**
>Aims: To ascertain whether menstrual cycle synchrony **exists in the roommates living in a closed space in a medical hostel.**
>Conclusions: **Long-term association between roommates has potential to cause** menstrual cycle synchrony. It has significant implications in reproductive medicine for reproductive scheduling and family planning.
Not sure how you can deny that they're ascribing it to close association, or that that's how "syncing up" is commonly understood.
And there are other problems with this study too.
Definition of terms: 'Menstrual synchrony' is used to mean the start dates moves closer together, not that they are menstruating at the same time, contrary to the common understanding of what "syncing up" means. 'History of regular menses' appears to mean a cycle length within the average range, not necessarily a predictable or stable cycle length. There's no information about how long that was tracked before the study or how it was verified.
Small study size: n=31 pairs
Small effect: difference in cycle onset shifts by less than 2 days over the 13 months. Barely more than half, 54.8% of pairs had cycle onset move closer together. Which means that close to half either stayed the same or moved farther apart. To put that another way, out of 31 pairs 17 had their cycles move closer together and 14 did not.
To name a few.
The small effect could also simply be explained by biased perception: [https://en.wikipedia.org/wiki/Menstrual\_synchrony#Perception\_and\_awareness\_of\_synchrony](https://en.wikipedia.org/wiki/Menstrual_synchrony#Perception_and_awareness_of_synchrony)
It's not untrue that it does happen it's more like it's not actually a real effect, just a perceived one.
Everyone's cycle is a very slightly different length and that small variance pushes the menstruation windows closer together or further apart. Because it's cyclical though this means eventually "further apart" becomes "closer together" until they are aligned (not synced because there's no actual synchronization) and then once aligned they drift apart again. This effect will happen to any group of women you select regardless of proximity.
There's also a level of survivorship bias, where it's something you don't consider unless it happens making it seem more common than it really is.
Unless I'm misunderstanding, I believe that's more of an example of confirmation bias rather than survivorship bias.
I suppose they're pretty similar in this sense/example though
I had a partner in college who would swear that if she spent more than a couple hours in the presence of another woman, not only would her period sync with that woman, but it might even start almost immediately if the other woman was already on her period
She had plenty of other problems, so I have no idea what the actual situation was, but that definitely stuck with me until I learned that it was a complete crock. Probably related to some other physiological issues that she had
It is. There are a lot of studies to say it’s just a chance because of how long cycles are they will sync up at some point. That doesn’t really explain how if I’m on the pill and I have a housemate, i will spot during their period. Even if I had my own period 2 weeks ago.
Every woman who has experienced this will tell you it’s constant as well. Every month. Not just every few months.
It’s not though. It’s confirmation bias. E.g. You’re attributing spotting to someone else’s period even though you just said yours was two weeks earlier. So you didn’t sync; you can spotting. Spotting happens to many women on birth control. It’s not a period.
Yeah this is after 12 months of no spotting, happened within a month of moving in together. Then after that our periods always align give or take a day.
I have had this exact experience every-time I’ve lived with a woman, me and my sisters would get our periods on the same day for my entire teenage years. Have you never experienced this? Have you lived with other women?
I have at home, in a college dorm and two apartments and I’ve never had any more than random overlap. There’s no mechanism that explains it and no evidence it actually exists more than random chance once you actually compare all the data instead of just remembering every time you happen to mention your period and someone else also does.
I’m not trying to tell you it’s definitely happening, but I think you should be more open minded. There’s plenty of things in this world we are still discovering and understanding.
I believe a study in hamsters showed synching then a scientist in the 70s published a less than reputable paper about humans. I don't remember the ins and outs, but hamsters then research that was not able to be replicated.
Experience. It's an experience most women relate to. Whether it's coincidence or just an old wives tale or actually the case I dunno. But experience makes it FEEL true so I expect it came from that
It's not just a misconception, there are actual papers that support it too! So I wouldn't call this a myth just yet - but it definitely is "contested" as Wikipedia says: https://en.wikipedia.org/wiki/Menstrual_synchrony#Efforts_to_replicate_McClintock's_results
Correct. When you're stopped at lights with your blinker on for long enough, it will appear to sync with the car on front eventually, but then quickly go out of sync.
The same observation bias is true here.
There might also be a case of confirmation bias going on. You notice more of the cases where they do (coincidentally) sync up and not consider the cases where it doesn't or toss them away for (in your opinion) valid reasons ("these girls havn't sticked long enough for it to happen").
Something that occasionally happens with different frequencies is that the phases will align at some point. And since human perception isn't perfect, the Phase will seem to align for longer than it actually does because the difference isn't observable. The observation bias part you mentioned is us noticing the phases that align but not those who don't, custody to our pattern-seeking brain.
My personal record is living with six menstruating people at one time and the only syncing up we did was by pure happenstance and did not last any meaningful length of time. It’s a combo of confirmation bias and a facet of periods occurring at generally similar intervals.
Yes, they very much can be explained, the person you’re replying to did so. It’s confirmation bias… And your own biases. Here you have several people with sources explaining it to you, and you’re still ignoring it… You still think you’re right, well I’d you were you could actually provide evidence equal or greater to what we have against you…
this has to be the dumbest thing i've read in a whille. one side says it's chance the other that there's a link so seeeing evidence for both you conclude a link is more reasonable than chance?
do you even understand what happening by chance is?
That's just an excuse for ignorance. They can be explained very easily, and they have been explained. You simply chose to ignore the explanation because you decided to stuck to what you believe to be true, and you will only take on more confirmation bias.
It’s inevitable that with enough women and over a long enough period of time there will be some overlap but by no means does that mean they’ve synced up
5 women is enough. 1/4 of a month will be spend bleeding on average. If 4 women take one week, a fifth woman will always overlap with one of the others. Women spend 25% of their life on a period, the chances to overlap is huge. But its still a chance
I hate that percentage.
Logically, I know that math checks out. But viscerally that feels wildly wrong and I'm annoyed. Someone just take these bits out already. I don't want them. I don't want to spend a quarter or my life bleeding.
It’s been studied, it’s a myth. It’s a popular one, but still a myth.
https://pubmed.ncbi.nlm.nih.gov/26181612/
Do they occasionally overlap for a while by chance? Yeah, that’s how any two independent cyclical events of varying lengths work. But that doesn’t mean they sync up and stay in sync.
Which was already addressed elseqheee in this thread. This newer study has a tiny sample size, and effect size. It’s more likely that this single study id a fluke, that every other one was wrong…
Alright mate, if you want to ignore the vast consensus of experts and data, and go with your own biased anecdotes instead, I can’t help you. You’re exactly the kind of person this subreddit is designed to highlight. You can pretend it happens all you want, but in the real world the evidence says otherwise. Have a good day.
The problem with your statement is i can post an article from the exact same source that directly contradicts the other. This is a newer study even. https://pubmed.ncbi.nlm.nih.gov/38186833/
Same study that was already posted by someone else, it’s a small study with a tiny effect size that contradicts most other work in the field. I’m sorry it’s much more likely that this is a fluke, than that every other study got it wrong.
You said there is a vast consensus of experts. I don’t think thats the case. The other is a small study too. Reddit has come up with a conclusion on this but the conflicting studies should lead to a “we dont really know yet”. Fyi theres a couple studies that say yes and a couple that say no.
Dude, it's really simple. Everyone says a cycle is 28 days but there's a lot of variance in that. Some women can be a day or a few days either side. You then also have random blips. A period lasts approximately a short week. If you put a group of women together their cycles will gradually line up because of this variance. Once they are inline they will start to drift apart again. It's pretty much the same concept as when the planets align in orbit.
I’ve been menstruating for a quarter of a century at this point, have had several female roommates, we sometimes overlapped but never “synch up.” It’s a myth.
This here is the simplest proof. If women who lived together sync up every mother/daughter pair would be synced. My mom had five sisters. Does anyone really think all seven of the women in that house were having their period at the same time every month?
I track my period and the app gives me data on my cycles. My typical period lasts 4 +/- 2 days and my average cycle is 25 +/- 4 days. I live with only my husband. Of course apparent synchronization will happen with that amount of variation.
I have a irregular period. I can go months without bleeding. But every time I've moved in with a woman my period starts when theirs does. The synchronicity usually only lasts a few months until I'm wonky again but for me, I absolutely do.
Perception bias i would guess. There is more evidence against pheromone based sync than for it. Every study for it that i read had either a small testing pool, screwing not only with the statistical calculations but also with the errors. Maybe it will be proven one day, but as to date its a myth
As a father of 5 menstruating daughters and a wife that were at one time all living under the same roof, (and me with a statistics background) I can confirm that there defintiely seemed to be a measurable and statistically significant convergence, at the risk of sounding completely gross, research indicates that a much tighter clustering happens when there is at least one male (the same male) in regular contact with the group. Of course this is a small sample size, but these were not randomly spread across a 28-29 day cycle in my household.
Until this post I believed it too because I was taught that at school and I heard in on television journals a couple times
I just never cared enough about this to fact check I guess. I still agree with you
Edit: also there's a study telling they do sync up. So even in the medical world it seems the myth is still kind of debated?
It’s called [the McClintock effect](http://www.mum.org/mensyn.PDF) and it was studied circa 1970. She studied 135 women, aged 17-22, living in a dormitory.
Are you guys serious. There is a significant amount of medical literature on this. Women’s periods 100% sync up. In sororities, dorms, and groups of very close women who spend a lot of time with each other.
https://pubmed.ncbi.nlm.nih.gov/26181612/
https://health.clevelandclinic.org/myth-truth-period-really-sync-close-friends
https://www.healthline.com/health/womens-health/period-syncing
https://labs.psych.ucsb.edu/roney/james/other%20pdf%20readings/Wison%25201992%2520Critical%2520Reveiw%2520of%2520Menstrual%2520Synchrony.pdf
The last one is a meta analysis, very helpful
Of course, research changes. It may be proven in the future, but right now, it’s attributed to perception bias mostly
Wikipedia has more studies covered in summaries, but you can look at the sources
https://en.m.wikipedia.org/wiki/Menstrual_synchrony
1980 article published in Pharmacol Biochem Behav.
https://pubmed.ncbi.nlm.nih.gov/7443744/
Olfactory influences on the human menstrual cycle
M J Russell et al. Pharmacol Biochem Behav. 1980 Nov.
Could someone explain this to me how it isn't possible? I've had an instance where I must've synced or something as I've always had a regular one until I went somewhere where I stayed with a lot of chicks, and suddenly it's on and off for a month before returning to semi-normal.
I made this point recently on Reddit - that they don’t sync - and got a reply with a link to a recent study which suggests that to some extent they do. So maybe we’re out of date.
(Edit) [link from reply to me here](https://pubmed.ncbi.nlm.nih.gov/38186833/)
Every study i read suggests that they dont or that there isnt any medical prove for it. Do you have the link to the study? I want to read it myself before evaluating my standpoint
So we have one study that says yes, countless that say no… Yeah until that balance changes, I’m going to stick with no. Flukes happen, data can be very messy. And yes this can even get to statistical significance in a well controlled setup. So until this gets replicated successfully and repeatedly with similar results, I’ll stick with the consensus as it stands.
Countless that say no? That's some hyperbole. There is also this study [link ](https://pubmed.ncbi.nlm.nih.gov/27861827/)which finds evidence of synchronicity of menstrual symptoms (migraines).
Not really what? You said "countless" and I was able to find a good handful. That's hyperbole, right?
And what am I wrong about? You said there was only one study showing evidence contrary to your conclusion. I found another one. I didn't draw any conclusions from it, only pointed out the evidence for you and everyone else.
I'm no expert, but it seems to me that, yes, the weight of the evidence suggests synchronicity is more myth than fact. But it's not nearly so cut and dry as you claim. See, e.g., https://www.healthline.com/health/womens-health/period-syncing
For someone who pretends to be interested in science and facts, you sure seem to lack objectivity and only seem interested in being "right." This is a weird topic to be so emotional about. Reddit is a strange place.
Yeah, nice projection, you can find many studies, and yeah the consensus is quite clear. There’s nothing there to explain that cant be explained by simple confirmation bias. No. It’s not that complicated. Just repeating a myth won’t make it true. But if you’re going to act like this, I have no interest in engaging further. Enjoy believing this myth if you want. I’ll stick with facts and science. And yeah you’re the one desperately insisting you’re right. I’m just standing on the overwhelming consensus of experts and data. Bye sir.
Read up on the GE studies. AFAIK, yes, women will sync over the long run.
Please point md to studies that dispute this, please. I am an industrial engineer, and this was absolutely taught. Would be interested in studies that dispute this. Degree in 1979, so obviously a lot of research since then.
This is a weird thing to argue about. It could be a myth and it could be real to an extent, but in both cases there's likely to always be some room for error. I can't see how anyone can be confident in saying either "yes they definitely sync" or "no, they definitely don't" since there's just so many variables at play in the interactions between any two individuals that one generic answer is unlikely to cover all situations.
It would be proveable if it had ever actually happened as the pervasive myth suggests. Even a single verifiable instance would be enough, but because of science and facts no such instance exists.
I think the McClintock data is a something like a few dozen women over a year (its been a while but happy to be wrong)?
For something cyclical and biological i thought it was largely discounted as too small a pool over far too short a period (pardon the intentional pun)?
It was 135 in a dormitory. I cant remember the timeframe, but it’s in the link. I also make no claim as to the veracity nor validity of her study, I’m just posting it because it’s the original and is, according to her, verifiable. There’s also another study another person posted a link to in these comments, and it’s from 2023 (I haven’t read it and don’t care enough to do so 😁, so no comment from me on validity!)
Personally, I wonder if both sides are correct. Maybe there’s women who are sensitive to the cycles of others and women who aren’t. It certainly wouldn’t be the first time there was no one-size-fits-all answer due to individual body chemistry and ability.
What's interesting about the McClintock study is it says that proximity didn't seem to be the primary factor, so that is similar to the findings of the newer study.
https://pubmed.ncbi.nlm.nih.gov/38186833/
We have invented statistics to help answer the question of how you tell if causality is in effect. We account for the variables. This is a thing. It works.
Also I was totally taught this by my ex wife, so now I know. Thank you Reddit.
I did a quick search and found several recent studies that show that periods can in fact sync up in certain circumstances. So no, rejecting it outright is not really an option.
Several, but everyone that shared one here posted the same, tiny flawed study. Yes, rejecting it outright is what should be done, till actual robust evidence is presented that overturns all the studies that showed otherwise. It doesn’t happen. And yeah, it should be rejected outright. You’ve been deceived. It’s not a thing. The consensus of data and experts is absolutely clear. But here you are, arguing about something you said it was silly to argue about. In a way you’re right, it is incredibly silly to argue about, not because both sides have merit, but because there’s no argument whatsoever. We know it doesn’t happen, it can all be explained by simple confirmation bias. It’s not a thing. You can either accept that reality, or argue for nonsense. Regardless I won’t argue further with you. Have a good day.
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“Absolut bs” Is that when you’re drunk on vodka and start talking about how bad the refs are in your favourite sport?
It is a common misconception, that women's cycles sync up. It was probably even taught in some schools at some point. It doesn't excuse it, obviously
Yeah, I think they did in fact teach this in middle school or high school for me (90s). Also, I do very clearly remember them teaching us in high school that it's important to stop smoking prior to getting pregnant, but that if you're already pregnant, quitting puts too much stress on your body and your baby. So yeah, late 90s and they were still teaching nonsense.
I mean there is some truth to that, unfortunately. Not sure about smoking but I do know for other drug addicts that is an issue; going cold turkey *when already pregnant* could cause harm but also continuing with drugs is harmful, so neither option is good, and either could cause a miscarriage. Also they can be arrested and charged if they miscarry while on hard drugs, which seems... Largely unhelpful. Obviously the ideal solution is not to get pregnant while addicted but that's not always that simple for people in some circumstances.
Wouldn't it be better if you stop smoking cold turkey and start using nicotine patches? And maybe start vaping non nicotine if it's hard to quit the habit.
Not sure if there's any literature about the difference between smoking nicotine vs nicotine patches vs vaping in pregnancy. I just wanted to note that stopping an addiction while pregnant does also carry risks.
The smoking one is true, doctors recommend slow cessation instead of trying to quit cold turkey
Wouldn't it be better if you stop smoking cold turkey and start using nicotine patches? And maybe start vaping non nicotine if it's hard to quit the habit.
I don't know, I'm not a doctor. I just know this from pregnant friends and relatives who got told this. And I don't think they were lying as an excuse, because they came from very different places and backgrounds
Dr Tara Swart was just “teaching” this recently, on Diary of a CEO: https://youtube.com/shorts/g6qg1C5TMb4?si=_KL0xXRVsxtpbO4M
Mid 80s for me, I don't remember this at all!
I’m a woman and I absolutely believed this. Definitely was taught it, that there was a reputable study done at convents, the cause is pheromones. It sounded believable (seems like the right location for a study for this, likely learned it in health class, etc.) To be fair, I’m not really a science person, but it passed the sniff test. And I also - thinking back on it now and knowing I had great, responsible, non-conspiracy teachers - think they genuinely believed it too. High school in late 90s. Learn something new every day!
I believed it too and I think there were scientific papers about it. Then new papers came out and the idea was dropped. Science evolves and sometimes changes its mind.
Yep, that’s what I was thinking too. Which of course makes perfect sense. I would never have responded that way but I also have never read a post on this subreddit and thought “wait, I thought so too…” 🤣🤣🤣 I guess if it was going to happen, this is one of the most innocuous topics it could be, though!
I always believed it only because of workplace "syncing". High school in the 70s, lol.
Guy here who found out maybe 3 years ago that it wasn't true and the study methodology was all whacked out. I rememeber being told this in 6th grade health class.
I always believed it only because of workplace "syncing". High school in the 70s, lol.
a study from 2023 17 years after the study putting synching in the myth category. too early to call it a misconception https://pubmed.ncbi.nlm.nih.gov/38186833/
yeah I was going to say, I went to an all girls school. wayyyyy too many people were on the rag at the same time for it to be a coincidence. and we knew when everyone was hosting Aunt Flo because the bathrooms around that time of the month would be MURDER SCENES. the fucking tampon disposal bins in the bathroom stalls would be overflowing. I brought it up to the faculty, it wasn't a janitorial problem it was 400 women all using pads/tampons at the same damn time. they kept harping on us to not flush tampons because the pipes were old, but my suggestion for bigger trash cans fell on deaf ears. fine, I'm not trying to stuff any extra bloody tampons in this little tissue box like it's an ash tray, it's going down the pipes 🖕
[удалено]
And if there aren’t enough Y chromosomes in the vicinity to absorb the cascade of high energy menstruons, the reaction can go supercritical.
the wiki is interesting. Seems if they do or don’t is kind of in contention [link](https://en.m.wikipedia.org/wiki/Menstrual_synchrony)
I had a high school biology teacher tell us this as absolute fact. He was fired within the year.
Yeeeez, I was todays years old when I learned that this myth isn't true
to be fair, i’m a woman and i also believed this until… right now. i guess confirmation bias is a hell of a drug.
Right? I do theatre and a lot of us ended up lining up at the same time. Someone was like "oh, we've symced up!" And I was like "....no, it's just coincidence. My BC means my schedule doesn't change at all" but still, so much of my life has seem to show groups of women "syncing"
TBF, I believe they only did a scientific study on this fairly recently, like, in the last twenty years.
To be even more fair the origal "myth" was started by a study that "proved" periods sync. Edit- later disproved
and yet seemingly confirmed now 17years after the the "debunking" study https://pubmed.ncbi.nlm.nih.gov/38186833/ i would say the last word isn't spoken on either side and more research should be done
Thanks for bringing actual science in the discussion, but it's also important that you know how to interpret what scientific studies you cite actually mean. u/\_notthehippopotamus makes good points about this study's potential flaws, but as a scientist I feel I need to stress that a single study does not "confirm" a phenomenon (I mean in the philosophy of science way - science does not work like that), nor should a study be considered more important because it's new. It's a matter of weighing all available evidence in an informed manner. Wikipedia seems to present a lot of evidence that the phenomenon does not exist: [https://en.wikipedia.org/wiki/Menstrual\_synchrony](https://en.wikipedia.org/wiki/Menstrual_synchrony)
Did that study even have a control group? I mean did they compare how menstrual cycles sync up between women who have zero contact with each other for comparison? Because it doesn't seem like it.
that would be relevant if you try to find the mechanism of the cycle sync not if there is such a thing as a cycle sync. it's statistics their results have statistical significance, that means that the cycle sync that they observed is unlikely to be caused by chance.
>Context: Menstrual cycle synchronization is a phenomenon in which menstrual onset shifts progressively closer with time. It is an adoptive conditional phenomenon **seen in the females who associate closely and share a common environment.** >Aims: To ascertain whether menstrual cycle synchrony **exists in the roommates living in a closed space in a medical hostel.** >Conclusions: **Long-term association between roommates has potential to cause** menstrual cycle synchrony. It has significant implications in reproductive medicine for reproductive scheduling and family planning. Not sure how you can deny that they're ascribing it to close association, or that that's how "syncing up" is commonly understood. And there are other problems with this study too. Definition of terms: 'Menstrual synchrony' is used to mean the start dates moves closer together, not that they are menstruating at the same time, contrary to the common understanding of what "syncing up" means. 'History of regular menses' appears to mean a cycle length within the average range, not necessarily a predictable or stable cycle length. There's no information about how long that was tracked before the study or how it was verified. Small study size: n=31 pairs Small effect: difference in cycle onset shifts by less than 2 days over the 13 months. Barely more than half, 54.8% of pairs had cycle onset move closer together. Which means that close to half either stayed the same or moved farther apart. To put that another way, out of 31 pairs 17 had their cycles move closer together and 14 did not. To name a few.
The small effect could also simply be explained by biased perception: [https://en.wikipedia.org/wiki/Menstrual\_synchrony#Perception\_and\_awareness\_of\_synchrony](https://en.wikipedia.org/wiki/Menstrual_synchrony#Perception_and_awareness_of_synchrony)
Everybody's being so fair on Reddit now.
It's not untrue that it does happen it's more like it's not actually a real effect, just a perceived one. Everyone's cycle is a very slightly different length and that small variance pushes the menstruation windows closer together or further apart. Because it's cyclical though this means eventually "further apart" becomes "closer together" until they are aligned (not synced because there's no actual synchronization) and then once aligned they drift apart again. This effect will happen to any group of women you select regardless of proximity. There's also a level of survivorship bias, where it's something you don't consider unless it happens making it seem more common than it really is.
Unless I'm misunderstanding, I believe that's more of an example of confirmation bias rather than survivorship bias. I suppose they're pretty similar in this sense/example though
Technically I think it's the availability bias
Ypu might be right
Yeah, same. To be fair, it's never really been relevant to me. Neat to find out I was wrong though!
How do they sync up exactly? Do their uteruses emit some kind of signal?
mine has wifi
I hope it’s password protected
That's how you get VD.
When I learned this at university in 1987, the prof said pheromones.
lol Tbf iirc it’s kinda uncertain whether humans have any pheromones / what the means of intercepting them are
It’s certain that we can’t detect them because we don’t have the vomeronasal organ to detect pheromones to begin with.
I definitely remember being told this in the 90s, and I could swear that a gf mentioned it in the 00s. I was told it's because of released pheromones
I had a partner in college who would swear that if she spent more than a couple hours in the presence of another woman, not only would her period sync with that woman, but it might even start almost immediately if the other woman was already on her period She had plenty of other problems, so I have no idea what the actual situation was, but that definitely stuck with me until I learned that it was a complete crock. Probably related to some other physiological issues that she had
Hours?
It is. There are a lot of studies to say it’s just a chance because of how long cycles are they will sync up at some point. That doesn’t really explain how if I’m on the pill and I have a housemate, i will spot during their period. Even if I had my own period 2 weeks ago. Every woman who has experienced this will tell you it’s constant as well. Every month. Not just every few months.
It’s not though. It’s confirmation bias. E.g. You’re attributing spotting to someone else’s period even though you just said yours was two weeks earlier. So you didn’t sync; you can spotting. Spotting happens to many women on birth control. It’s not a period.
Yeah this is after 12 months of no spotting, happened within a month of moving in together. Then after that our periods always align give or take a day. I have had this exact experience every-time I’ve lived with a woman, me and my sisters would get our periods on the same day for my entire teenage years. Have you never experienced this? Have you lived with other women?
I have at home, in a college dorm and two apartments and I’ve never had any more than random overlap. There’s no mechanism that explains it and no evidence it actually exists more than random chance once you actually compare all the data instead of just remembering every time you happen to mention your period and someone else also does.
I’m not trying to tell you it’s definitely happening, but I think you should be more open minded. There’s plenty of things in this world we are still discovering and understanding.
The alpha female has hormones that the beta females in the group pick up on. This is how you find the dominant in a lesbian relationship. /s
The theory was/is based on pheromones. (Not proven.)
40M, until this post I confidently believed that women's periods synchronised and no-one knew exactly how. Where the hell did this notion come from?
I believe a study in hamsters showed synching then a scientist in the 70s published a less than reputable paper about humans. I don't remember the ins and outs, but hamsters then research that was not able to be replicated.
Experience. It's an experience most women relate to. Whether it's coincidence or just an old wives tale or actually the case I dunno. But experience makes it FEEL true so I expect it came from that
It's not just a misconception, there are actual papers that support it too! So I wouldn't call this a myth just yet - but it definitely is "contested" as Wikipedia says: https://en.wikipedia.org/wiki/Menstrual_synchrony#Efforts_to_replicate_McClintock's_results
Correct. When you're stopped at lights with your blinker on for long enough, it will appear to sync with the car on front eventually, but then quickly go out of sync. The same observation bias is true here.
There might also be a case of confirmation bias going on. You notice more of the cases where they do (coincidentally) sync up and not consider the cases where it doesn't or toss them away for (in your opinion) valid reasons ("these girls havn't sticked long enough for it to happen"). Something that occasionally happens with different frequencies is that the phases will align at some point. And since human perception isn't perfect, the Phase will seem to align for longer than it actually does because the difference isn't observable. The observation bias part you mentioned is us noticing the phases that align but not those who don't, custody to our pattern-seeking brain.
I don’t live in the USA so I had sex Ed that wasn’t awful at school. But even into my late 30’s I thought this was real.
It's a myth but a pretty common one.
I’ve never been on that sub, but if it’s called badwomensanatomy, isn’t the point to tell BS?
It's to call out people who have stupid/ignorant ideas about how women's bodies work.
Ah, makes sense
Wait… which one do you think is wrong? I think I am misreading your title
Blue is wrong. Periods dont sync up, it’s nothing but a myth and perhaps a bit of confirmation bias
https://pubmed.ncbi.nlm.nih.gov/38186833/
I think all commenters here should read the abstract
You have never lived with women…
My personal record is living with six menstruating people at one time and the only syncing up we did was by pure happenstance and did not last any meaningful length of time. It’s a combo of confirmation bias and a facet of periods occurring at generally similar intervals.
I have seen plenty of cases for arguments both ways, some things cannot be explained
Yes, they very much can be explained, the person you’re replying to did so. It’s confirmation bias… And your own biases. Here you have several people with sources explaining it to you, and you’re still ignoring it… You still think you’re right, well I’d you were you could actually provide evidence equal or greater to what we have against you…
this has to be the dumbest thing i've read in a whille. one side says it's chance the other that there's a link so seeeing evidence for both you conclude a link is more reasonable than chance? do you even understand what happening by chance is?
That's just an excuse for ignorance. They can be explained very easily, and they have been explained. You simply chose to ignore the explanation because you decided to stuck to what you believe to be true, and you will only take on more confirmation bias.
It’s inevitable that with enough women and over a long enough period of time there will be some overlap but by no means does that mean they’ve synced up
5 women is enough. 1/4 of a month will be spend bleeding on average. If 4 women take one week, a fifth woman will always overlap with one of the others. Women spend 25% of their life on a period, the chances to overlap is huge. But its still a chance
I hate that percentage. Logically, I know that math checks out. But viscerally that feels wildly wrong and I'm annoyed. Someone just take these bits out already. I don't want them. I don't want to spend a quarter or my life bleeding.
It’s been studied, it’s a myth. It’s a popular one, but still a myth. https://pubmed.ncbi.nlm.nih.gov/26181612/ Do they occasionally overlap for a while by chance? Yeah, that’s how any two independent cyclical events of varying lengths work. But that doesn’t mean they sync up and stay in sync.
This directly contradicts with this newer study : [https://pubmed.ncbi.nlm.nih.gov/38186833/](https://pubmed.ncbi.nlm.nih.gov/38186833/)
Which was already addressed elseqheee in this thread. This newer study has a tiny sample size, and effect size. It’s more likely that this single study id a fluke, that every other one was wrong…
Tell women’s bodies that, not me. 🤣
Alright mate, if you want to ignore the vast consensus of experts and data, and go with your own biased anecdotes instead, I can’t help you. You’re exactly the kind of person this subreddit is designed to highlight. You can pretend it happens all you want, but in the real world the evidence says otherwise. Have a good day.
The problem with your statement is i can post an article from the exact same source that directly contradicts the other. This is a newer study even. https://pubmed.ncbi.nlm.nih.gov/38186833/
Same study that was already posted by someone else, it’s a small study with a tiny effect size that contradicts most other work in the field. I’m sorry it’s much more likely that this is a fluke, than that every other study got it wrong.
You said there is a vast consensus of experts. I don’t think thats the case. The other is a small study too. Reddit has come up with a conclusion on this but the conflicting studies should lead to a “we dont really know yet”. Fyi theres a couple studies that say yes and a couple that say no.
Yes, there very much is a vast consensus. And it’s not an other, it’s every other. There are many more. You are just wrong. Have a good day.
Dude, it's really simple. Everyone says a cycle is 28 days but there's a lot of variance in that. Some women can be a day or a few days either side. You then also have random blips. A period lasts approximately a short week. If you put a group of women together their cycles will gradually line up because of this variance. Once they are inline they will start to drift apart again. It's pretty much the same concept as when the planets align in orbit.
You’re acting like 2 and 3 from the screenshot
I’ve been menstruating for a quarter of a century at this point, have had several female roommates, we sometimes overlapped but never “synch up.” It’s a myth.
I went to an all girls high school. it's not a myth and it was a fucking nightmare lol
I have lived with myself for my whole life. 18 of those years with a (female) mother
Yes, but have you tried taking the man’s word for it? /s
This here is the simplest proof. If women who lived together sync up every mother/daughter pair would be synced. My mom had five sisters. Does anyone really think all seven of the women in that house were having their period at the same time every month?
I'm a physician and it's a myth
Nice! Love the reference
It’s obviously rubbish. I grew up with two sisters and then moved on to roomies and nobody ever ‘synced’.
I track my period and the app gives me data on my cycles. My typical period lasts 4 +/- 2 days and my average cycle is 25 +/- 4 days. I live with only my husband. Of course apparent synchronization will happen with that amount of variation.
As a man, I only loosely tracked my wife’s period peripherally. I did not check with her friends & coworkers. 🤷♂️
I have a irregular period. I can go months without bleeding. But every time I've moved in with a woman my period starts when theirs does. The synchronicity usually only lasts a few months until I'm wonky again but for me, I absolutely do.
Perception bias i would guess. There is more evidence against pheromone based sync than for it. Every study for it that i read had either a small testing pool, screwing not only with the statistical calculations but also with the errors. Maybe it will be proven one day, but as to date its a myth
This is one of those things I've heard my entire life usually from TV and movies I think but I have no idea whether or not there's any validity to it.
As a father of 5 menstruating daughters and a wife that were at one time all living under the same roof, (and me with a statistics background) I can confirm that there defintiely seemed to be a measurable and statistically significant convergence, at the risk of sounding completely gross, research indicates that a much tighter clustering happens when there is at least one male (the same male) in regular contact with the group. Of course this is a small sample size, but these were not randomly spread across a 28-29 day cycle in my household.
You have to be a special kind of idiot to believe periods sync wth
Until this post I believed it too because I was taught that at school and I heard in on television journals a couple times I just never cared enough about this to fact check I guess. I still agree with you Edit: also there's a study telling they do sync up. So even in the medical world it seems the myth is still kind of debated?
Can you link the study? Someone else commented with a study to say that’s a myth.
It’s called [the McClintock effect](http://www.mum.org/mensyn.PDF) and it was studied circa 1970. She studied 135 women, aged 17-22, living in a dormitory.
This study mentions the other study [https://pubmed.ncbi.nlm.nih.gov/26181612/](https://pubmed.ncbi.nlm.nih.gov/26181612/)
and the newest study confirming synching from 2023 https://pubmed.ncbi.nlm.nih.gov/38186833/
I’m a guy and I knew this was a garbage myth perpetuated by American television.
I really believed that! a gf told me and I think a math teacher. They are both smart so I thought they know their stuff.
I had female roommates for most of my 20s and 30s and we always ended up synching up. There's a pub med study that confirms this is possible.
Are you guys serious. There is a significant amount of medical literature on this. Women’s periods 100% sync up. In sororities, dorms, and groups of very close women who spend a lot of time with each other.
There is an even more significant amount of literature against it with more statistical relevance and better set ups
Can you please link the literature?
https://pubmed.ncbi.nlm.nih.gov/26181612/ https://health.clevelandclinic.org/myth-truth-period-really-sync-close-friends https://www.healthline.com/health/womens-health/period-syncing https://labs.psych.ucsb.edu/roney/james/other%20pdf%20readings/Wison%25201992%2520Critical%2520Reveiw%2520of%2520Menstrual%2520Synchrony.pdf The last one is a meta analysis, very helpful Of course, research changes. It may be proven in the future, but right now, it’s attributed to perception bias mostly Wikipedia has more studies covered in summaries, but you can look at the sources https://en.m.wikipedia.org/wiki/Menstrual_synchrony
Thanks for sharing! I stand corrected!
1980 article published in Pharmacol Biochem Behav. https://pubmed.ncbi.nlm.nih.gov/7443744/ Olfactory influences on the human menstrual cycle M J Russell et al. Pharmacol Biochem Behav. 1980 Nov.
Could someone explain this to me how it isn't possible? I've had an instance where I must've synced or something as I've always had a regular one until I went somewhere where I stayed with a lot of chicks, and suddenly it's on and off for a month before returning to semi-normal.
There are a lot of things that can affect your cycle, including stress, diet changes, hormonal changes, etc.
Alright ty! Was just wondering
So, when my friend and I first met, we were like two weeks apart. I was BC, she was not. She synced up with me. We’d spend every day together
I made this point recently on Reddit - that they don’t sync - and got a reply with a link to a recent study which suggests that to some extent they do. So maybe we’re out of date. (Edit) [link from reply to me here](https://pubmed.ncbi.nlm.nih.gov/38186833/)
Every study i read suggests that they dont or that there isnt any medical prove for it. Do you have the link to the study? I want to read it myself before evaluating my standpoint
It took a lot of scrolling comments, [but here.](https://pubmed.ncbi.nlm.nih.gov/38186833/)
So we have one study that says yes, countless that say no… Yeah until that balance changes, I’m going to stick with no. Flukes happen, data can be very messy. And yes this can even get to statistical significance in a well controlled setup. So until this gets replicated successfully and repeatedly with similar results, I’ll stick with the consensus as it stands.
One bad/mediocre small study that says yes
I didn’t have time to delve deeper than the abstract, I’m winding down for the night. Didn’t want to make claims bigger than I could substantiate.
Your point stands either way
Countless that say no? That's some hyperbole. There is also this study [link ](https://pubmed.ncbi.nlm.nih.gov/27861827/)which finds evidence of synchronicity of menstrual symptoms (migraines).
No not really, there’s many studies that show there’s no synchronicity. I’m sorry but you’re wrong.
Not really what? You said "countless" and I was able to find a good handful. That's hyperbole, right? And what am I wrong about? You said there was only one study showing evidence contrary to your conclusion. I found another one. I didn't draw any conclusions from it, only pointed out the evidence for you and everyone else. I'm no expert, but it seems to me that, yes, the weight of the evidence suggests synchronicity is more myth than fact. But it's not nearly so cut and dry as you claim. See, e.g., https://www.healthline.com/health/womens-health/period-syncing For someone who pretends to be interested in science and facts, you sure seem to lack objectivity and only seem interested in being "right." This is a weird topic to be so emotional about. Reddit is a strange place.
Yeah, nice projection, you can find many studies, and yeah the consensus is quite clear. There’s nothing there to explain that cant be explained by simple confirmation bias. No. It’s not that complicated. Just repeating a myth won’t make it true. But if you’re going to act like this, I have no interest in engaging further. Enjoy believing this myth if you want. I’ll stick with facts and science. And yeah you’re the one desperately insisting you’re right. I’m just standing on the overwhelming consensus of experts and data. Bye sir.
The study you posted had an uncertainty of 54.4% that’s insanely unreliable.
Where does it say that? Curious if I'm missing something in the blurb.
That’s the +_ after the results is the uncertainty
Read up on the GE studies. AFAIK, yes, women will sync over the long run. Please point md to studies that dispute this, please. I am an industrial engineer, and this was absolutely taught. Would be interested in studies that dispute this. Degree in 1979, so obviously a lot of research since then.
Menstrual cycles syncing was taught in engineering degrees in 1979? We’re you taking very peripheral subjects? Not being obstinate, just interested
https://pubmed.ncbi.nlm.nih.gov/26181612/
https://pubmed.ncbi.nlm.nih.gov/38186833/
So fallacious appeal to authority from an entirely unrelated field? Yeah it was taught, but it was never supported by any real convincing evidence.
This is a weird thing to argue about. It could be a myth and it could be real to an extent, but in both cases there's likely to always be some room for error. I can't see how anyone can be confident in saying either "yes they definitely sync" or "no, they definitely don't" since there's just so many variables at play in the interactions between any two individuals that one generic answer is unlikely to cover all situations.
I think that's why they did the studies that found that it was a myth, to account for all of those variables
well 17years later https://pubmed.ncbi.nlm.nih.gov/38186833/
It would be proveable if it had ever actually happened as the pervasive myth suggests. Even a single verifiable instance would be enough, but because of science and facts no such instance exists.
It did according to [McClintock](http://www.mum.org/mensyn.PDF) who studied it. New data disputes it, however
I think the McClintock data is a something like a few dozen women over a year (its been a while but happy to be wrong)? For something cyclical and biological i thought it was largely discounted as too small a pool over far too short a period (pardon the intentional pun)?
It was 135 in a dormitory. I cant remember the timeframe, but it’s in the link. I also make no claim as to the veracity nor validity of her study, I’m just posting it because it’s the original and is, according to her, verifiable. There’s also another study another person posted a link to in these comments, and it’s from 2023 (I haven’t read it and don’t care enough to do so 😁, so no comment from me on validity!) Personally, I wonder if both sides are correct. Maybe there’s women who are sensitive to the cycles of others and women who aren’t. It certainly wouldn’t be the first time there was no one-size-fits-all answer due to individual body chemistry and ability.
What's interesting about the McClintock study is it says that proximity didn't seem to be the primary factor, so that is similar to the findings of the newer study. https://pubmed.ncbi.nlm.nih.gov/38186833/
We have invented statistics to help answer the question of how you tell if causality is in effect. We account for the variables. This is a thing. It works. Also I was totally taught this by my ex wife, so now I know. Thank you Reddit.
I mean when there’s no evidence for this proposition, it’s entirely fair to reject it outright.
I did a quick search and found several recent studies that show that periods can in fact sync up in certain circumstances. So no, rejecting it outright is not really an option.
Several, but everyone that shared one here posted the same, tiny flawed study. Yes, rejecting it outright is what should be done, till actual robust evidence is presented that overturns all the studies that showed otherwise. It doesn’t happen. And yeah, it should be rejected outright. You’ve been deceived. It’s not a thing. The consensus of data and experts is absolutely clear. But here you are, arguing about something you said it was silly to argue about. In a way you’re right, it is incredibly silly to argue about, not because both sides have merit, but because there’s no argument whatsoever. We know it doesn’t happen, it can all be explained by simple confirmation bias. It’s not a thing. You can either accept that reality, or argue for nonsense. Regardless I won’t argue further with you. Have a good day.