Menstrual Synchrony

In reference to today’s column:

I can easily understand how a statistical fluke can give the impression of synchronicity. Statistics are slippery things even at their apparently most simple. It’s easy to see a group of women with nearly identical cycles “lining up” at one time and giving the impression that something other than chance was behind it all.

But Pepper Mill had a truly irregularly-spaced period, and she appeared to be causing the normally regular women in her group to have matching irregular periods. It was because of their complaints that she ultimately ended up on the pill as a way to “regularize” her timing. In this case, it’s hard to explain the synchronicity as just probability. Pepper’s group certainly thinks there’s something to the idea of influencing each other’s cycles.

On a similar note, I lived in a coed fraternity house when I was an undergrad. One of the women who lived there had a cycle of approximately fifty days. Seriously. Since this was normal for her, it wasn’t something she typically went around worrying about at length. A few months into the fall semester, every other woman who lived on the same floor she did started experiencing longer cycles. By the end of the year, most of them were having cycles that matched hers pretty closely. Since none of them realized that this one woman had freakishly long cycles to begin with, they all thought they were late, every month.

I would describe the row of pregnancy tests lined up on the bathroom counter every six weeks to be unbiased evidence, not subject to statistical trickery. It’s too bad we didn’t run a controlled experiment at the time. She could have published a paper.

I can only offer anecdotal evidence as well.

Lady Chance had the same dorm roomie for three years. Roomie had a cycle of two months when they started rooming together but gradually came to the one month cycle over the first year. Roomie was never on the pill through this period so that couldn’t do it. Lady Chance was on the pill and had regular cycles.

She was actually pretty ticked off about it.

I don’t know if she diverged when they went their seperate ways. How would one ask?

Oh, and am I the only one who noted that the webmaster made the bullet points in this column red? That had to be done on purpose. The default is black. Ugh.

A second thought on Menstrual Synchrony… How many of the women in these studies are on the pill… Most pill manufacturers have the pills organized by day, so you start taking the placebo pills on a sunday,triggering the start of Menses… in the original study, performed on women in college, how many women were on the pill? if a significant percentage of them were, the possible days for onset goes from 28 to 4, further skewing the statistics.



Countervaling simulposts.

Bloody confirmation bias. It’s a curse, eh?

I notice Cecil is synching with The New Scientist’s “The Last Word” column by running with this matter this week. Coincidence?

Cecil seems to be a little ahead of the game - or at least more skeptical.

<insert rimshot sound effect here>

Probably. It’s hard to tell if Cecil and New Scientist are really synching, due to the small sample size.

I experienced menses synch at a job I used to have. There were 5 women in one office, and although some were on the pill and some weren’t, eventually all of us were on the exact same cycle! It took about 18 months IIRC. Our male boss was a little freaked out, as his entire department would bitch out at the same time!

In oder for this to happen, does it mean that those of us on the pill (whose cycles could not change) had the dominant pheremones or whatever, and changed the cycles of the non-pill users?


While I agree that the scientific evidence is doubtful, the experiential evidence is overwhelming. I was part of a group that had several women meeting several times a week for several hours at a time. Not even living together, we noticed that we all bled at the same time. Several of the women did live together. Perhaps their combined pheromonic input was enough to snyc the rest of us? Now I have a several-hours meeting with only one other woman once a week, and even with that we bleed at the same time. I haven’t asked what her cycle is, I just go by the wastebasket evidence. This is about the only time I see other women, so it may be enough to tip me over. Dunno.

The dissertation on Menstrual synchrony was so long, I actually forgot the question ! I do enjoy reading the column, and some(other)times, I actually learn something ! Thanks for allowing me to join the group of (probably) very interesting people !

Welcome to the SDMB, John.

I hope you enjoy your stay.

It was very amusing to see the attempted correlation between sperm ingestion and menstrual synchrony. Obviously, a man must have figured this one out. It has been studied in office environments as well as college dormitories that women DO thend to synchronize their periods. Usually it has been demonstrated that the more dominant women start their periods first. I presume it may have something related to pheremones. I have bred dogs for 27 years, and when a bitch comes into season, if the othes are anywhere near their time, all they have to do is be around the one in season for about 3 days, and they will come into season as well. .(No sperm ingestion…) It is understood in the dog show world. If you bring a new pup into a dog environ, eventually, that pup will synch with the more dominant bitches. This is ESPECIALLY handy when you have male dogs that drive you nuts, because it is all over and done with in 3 weeks. Maybe lesbians, (if indeed this non-synchronizing is a fact) have an unusual dominance mode, or maybe they don’t excrete those pheremones, because they don’t WANT to attract a man…ever. Just a thought, so keep wishing, fellas, us women are NOT going to ingest YOUR sperm just to be in Synch. We already ARE in Synch. Sammybarb:D

Actually, you know what??? I just heard a report that mens penises grow up to three inches longer when they routinely perform oral sex on women!!! Get busy, fellas! hehe, SammyBarb:D


Thanks for the welcome. I must say I REALLY enjoyed your “Countervaling simulposts” input. I’m convinced I will enjoy my stay.

:slight_smile: john

Ok, I suppose I shall have to throw my experiences into the ring. I am the mom of two teenage girls, one lives at college but is now home for the holidays. Before she left for school, the three of us all started within 1 day of each other. While at school, daughter 1’s cycle changed. She has been home for about 4 days now, and would start next week, per her college schedule. However, since her sister and I are in such perfect synch, her schedule is showing signs of changing as well.

How long did the 5 of you stay on the same cycle? This “convergence” at 18 months could have just been the time when all of the cycles-of-differing-length among the 5 women happened to hit their periods all at the same time.

Almost two years.

I think this is a case of anecdotal evidence run amok! I work in an office with about 60 women. I have noticed that whenever two or more women start their period on the same day, synchronicity comes up. That these same women don’t start their period on the same day the next month escapes notice. I have had a completely regular, 28 day cycle all of my life. My sister has a 25 day cycle. This has not changed for either of us. After all these years, shouldn’t my sister, my niece, and all my female friends be cycling together by now? It doesn’t even really make sense to me from a biological standpoint. What would be the advantage of having all the female population be alternately at their most fertile and least fertile at the same time? Wouldn’t it make more sense, biologically, to have the female population on a staggered schedule? If not, why the variability in our cycles? More importantly, where do I sign up to get at 50 or 60 day cycle as discussed above???:cool:

I don’t know about scientific evidence, but when I was in High School, I was in a dance troop of about twenty girls. We practiced almost everyday and would spend at least three to four hours a day together.

I remember that every single girl in the troop started their period on Opening Night of the Big Dance Show. It was quite amusing to say the least.

Seems to me that synchronicity is more likely to occur if the group of women is few in number. Coming from a large office with possibly 30 women to a small office of 6, my cycle changed to match theirs. Also, the 6 were in much closer quarters.

Since my daughter (living with me) went on the pill, my cycle has changed to match hers (I’m working from home now).