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October 6, 2010 • 21 mins

There's a commonly held belief that women's periods synchronize when they spend a lot of time together. This popular theory has a scientific basis, but more recent studies suggest that it's not actually valid. Tune in and learn more in this episode.

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Speaker 1 (00:00):
Brought to you by the reinvented two thousand twelve Camray.
It's ready. Are you welcome to stump Mom never told you?
From House to works dot Com. Hello, and welcome to
the podcast. This is Molly and I'm Kristin. Kristin, we

(00:20):
spend a lot of time in the stood together, Yes
we do. This is not the introduction you want me
to make. I'm betting I know. Keep going, Molly. I
want to see where this path leads is. I think
you know where it's going to lead us. Kristen don't
know the sparkle in your eye. I'm not really sure
where it's gonna lead us. Molly, you've already asked me
to marry you on one podcast. I beg your pardon,

(00:42):
Kristen Conger. You asked me to marry you? Really? Yes?
I don't remember it that way, Kristen Conger. Everyone better
write into Kristen Conger and remind her that she is she.
She has treated our marriage proposal with such disrespect, and
now she's trying to pin this on me. She wiggled
out of it, and so now I'm going to tell
an embarrassing story about her menstruation. Okay, No, I won't guys,

(01:06):
but that's the topic of today's episode, menstruation. We love
to talk about it. Yeah, welcome back, kiss It's Mom's
stuff menstruation Hour and uh, the question today is one
that's been off offt requested by our listeners. Coming myth
out there. It's a very common. In fact, one study
said that about of women buy into this myth. Is

(01:26):
it a myth? We'll get to that that women who
spent a lot of time together, as Christen and I
do in our booth, our booth of our womb, really
closed closet area. Um side Nope, Um, the women who
spent a lot of time together get in sync with
their menstrual cycles. Because how many times have you been like, oh, gosh,

(01:47):
I have the worst cramps. I'm just mom a period
and someone will be like me too, and then you're
like like, oh my gods. Yeah um. And you know,
the men can turn around and be like, if they're
a woman full of this, they might say women say
women full of office, They're in a women full of office.
If they're an office full of women, they'll be like,

(02:08):
everyone's on their period. Watch out. So yeah, it's something
that's that's batted around a lot. Yeah, and and and Molly,
I think that you and I can both agree this
is something. It just it just happens, you know, the
the moment when you're you know, complaining to to Galpal.
I think everyone spent in this moment about your menstrual moments,

(02:29):
because I feel like it is something of a hardcore
bonding moment when you know, in the in the in
the peak of your mentrual discomfort, a friend leans over
and says, girlfriend, same thing's happening to me. Yeah, exactly
makes you feel a little less alone because as we
just how als we have discussed about menstruation, it's a

(02:51):
private thing. No one talks about it. The fact that
you could even be just sharing it with someone kind
of comforting. And plus you know who to borrow tampons from.
To get to the root of whether or not women
do in fact sync up their minstrual cycles, we had
to go back to nineteen seventy one. This all starts
in nineteen seventy one with Martha McClinton. Yes, and she

(03:14):
was just an undergraduate, which is pretty impressive to me,
and as many undergraduates, dude, she noticed, Hey, all these
ladies who lived together, they tend to have their parents
at the same time. I think, like in a dorm setting,
women's dorm, Yeah, I mean in college. I mean I
think that's when you first maybe start to really notice
the fact that this can happen. Yeah once once you start, yeah,
you move out of your parents house and you're living

(03:35):
with other women, although if you're living with your mom,
that can affect things. Anyway, Martha noticed it when she
was at the Storm because it was an all female dorm.
Women overload boom. She decides to investigate and she publishes
her study in nineteen seventy one um Base and the
basis of her study was to ask a hundred thirty

(03:56):
five college girls to recall their periods start dates um
and the period before that start date at three times
during the year. So she had a total of six
period start dates, and she found that as the year
went on, the start dates got closer and closer together.
And I what I love about a menstrual synchrony study, Christen,

(04:17):
is that there usually has to be a really detailed
analysis of what the dorm looked like and just how
close the women were and where the common areas were,
and who was sharing a room with who, and who's
and whose friends with whom and how close of friends
are they? Yeah, it's it's very much turning uh college
drama into a paper starts because it's like, here's like

(04:39):
all the dorm here's who didn't like each other, here's
who had to live together anyway, did their periods sync up?
And so in that first nineteen seventy one study, McClintic
finds that, yes, they get closer together, that something is
affecting these women so that their menstrual periods start an end.
At the same time, she wasn't quite sure what it
was right and from just to be specific, from April

(05:00):
to October. Throughout the study, the close friends, the girls
who are and the girls who were living together, their
periods aligned two days closer um, which she found to
be a pretty significant result. And thanks to this, we
should say, thanks to the sensation that was this nineteen
seventy one study published in the journal Nature menstrual synchronization

(05:23):
also referred to as the McClintic effect. We will not
leave McClintic behind for this entire podcast. She she has
a recurring character just duck away. She might be the
starring role. I shouldn't call her recurring character. Now, let
me throw out some of the reasons she thought this
was happening, because she wasn't sure in nineteen seventy one
what was causing that. She considered perhaps it was the
fact they all ate in a common cafeteria, because there

(05:46):
are some species that it's more about times of plenty
that that changes their cycles more than than close proximity.
But she had also studied rats, and it was close
proximity that affected the rats. Um. She thought maybe the
moon had something to do with it, particularly if women.
If these women were like having steady groups late at
night and they were exposed to more light than they

(06:07):
would be if they had been asleep, like she thought,
maybe the light dark cycles were affecting them to write
because they've found what in like certain monkey species, they're
mentioned their men sees there a stress cycles are heavily
influenced by the moon, which she was wild sometimes we
will refer to menstruation as our moon cycle. Um. She

(06:29):
thought maybe it was just the amount of time people
spent together, which is why she asked all the girls
in the study to evaluate, like their best friend, the
person they saw the most the roommate, because maybe it
was just like during sleep that that the roommate was
influencing this. She thought maybe it might be men. So
she asked all the girls about relationship statuses, and then
one thing she throws in, you know, these ten reasons
where she's trying to figure out what's going on, she

(06:51):
mentioned pheromones. And pheromones are kind of controversial in whether
they exist in humans or not. Yeah, they No one
has ever really come to a conclusion about pheromones. It's
something that we can't really explain. But they're basically hormonal
signals that our bodies supposedly give off that influence that

(07:13):
other people have a physiological reaction to. And a lot
of times when we talk about pheromones, it's related to attraction,
Like you send off some kind of lusty signal to
John Hamm and he he picks up on it. Yeah,
and it's it's kind of controversial just because the mechanism
for picking up pheromones hasn't been definitively found in humans.

(07:35):
But I think we've talked about, like on our Lust podcast,
some animals you can see the organ that can pick
up these unconscious signals that we're all sending so um.
So she continues this work on pheromones and other people
are you know, at the same time that she's working
on these pheromones. I think people are confirming her study.
And then in n mcclinic comes up with a or

(07:57):
comes out with, I should say, a far allow up
study really driving home this ovulation pheromone connection, where she
says absolutely the pheromones that women produce have an effect
on other women's ovulation cycles. And she thinks that what
we're doing is sending each other messages about wins a

(08:19):
good time to have a baby, because if you look
at these ancient populations, then it's to your advantage to
be a mother with a bunch of other mothers. Your
brood has a better chance of surviving versus these broods
that it's just one one kid. Yeah, and it depends
on what phase uh in your cycle you're in, whether
you're in the luteal phase or the fellicular phase, basically

(08:41):
like how close you are to drop in that how
pregnant can you get? So I have to say she
says that women in the study didn't even know if
they were in the control group of the real group,
but I have to say, I don't know if the
study sounds very appealing for me to do, because what
it involves is taking a swab from an armpit of
a woman who is in one of these phases that

(09:03):
Kristen mentioned and giving it to another woman and seeing
if that swab, smelling that swab based on based on
where these women were, did it didn't affect their menstrual cycle. Yeah,
and mclinic says absolutely, she said, depending on she swabbed
for two different pheromones based on the where the women

(09:23):
were in their menstrual cycle, and she said that one
pheromone produced before ovulation would shorten the ovarian cycle of
the woman who you know was wearing this this underarm
patch around which her odorless. Again pho, it's like smell
right right, Um, it's not like you know, they're wearing

(09:43):
like someone's dirty laundry. But then the second pheromone, which
was produced at ovulation, would lengthen their cycles like this
is not a good time to get pregnant, way a
little longer. So she's found that you can affect menstruation
both ways. You can both shorten the side goal and
lengthen the cycle, depending on which pheromone produced at which

(10:04):
part of your cycle you can you're smelling, So she says, yes,
this is definite proof of both pheromones and of menstrual synchronization, right,
And we should say too that sixty percent of the
female participants experienced some kind of change alteration in their cycles,
but some women did not, so there was still kind

(10:26):
of this this other question of well, what is kind
of going on here? Why aren't the pheromones affecting everyone equally?
But still six percent pretty significant proportion. It's pretty significant.
So you know, throughout throughout this time, the Clintic is
doing all sorts of work with pheromones. One thing she
found is that, um, when when women smell a nursing

(10:46):
mother's pheromones, they too, uh, they experience more sexual desire.
But thought being that, uh, you know, they can smell
that another woman's had a baby and is nursing it.
It's a healthy baby, the woman's nursing healthfully, and we
want a baby. I want a baby, so I'm going
to feel so much sexual desire. I mean, they didn't
even measure whether it's been one baby. They asked them,
if you are with a man, do you feel like

(11:08):
having more sex. They were like yes. They were like,
if you are single, are you having more sexual fantasies?
The women were like yes. So this work um on pheromones.
I think it's really notable because it evaluates women's health
in a way that I don't think is evaluated that
often in the academic world. How often on this podcast
have we said women are understudied. They're not doing research

(11:30):
on women. They'll do the research on men, but not women.
So here's an example of how one woman's work has
really influenced a lot of a lot of work on
you know, sexual desire and opulation and when's the best
time to get pregnant. So I think that's pretty cool.
But but McClintic has some foes, friendly foes, I suppose

(11:52):
friendly foes, but mcclinic. Not everyone completely bought mcclintics synchrony theory.
In two thousand five, we have a pair of researchers
from the University of California and also from North Sichuan
Medical College in the People's Republic of China. They publish

(12:12):
a study and it's got a pretty pretty straightforward title. Molly,
you ready for this? Smack own? In my opinion. All right,
So the name of the study, published in the journal
Human Nature Winter two thousand six, quote, women do not
synchronize their menstrual cycles. Subtitle eat at mcclinic. I don't

(12:36):
see that subtitle on my copy. But you don't even applied.
It was pretty clear they broke down m clinics methodology
and said, I smell a rat. Here's something is not right.
I don't like how she collected her data. I don't
know like how she analyzed her data and applied statistical

(12:57):
analyzes to it. We're gonna do this again, and we're
gonna do it better. And uh, guess what, women don't synchronize.
No more bonding for you women. Stop stop talking about
your periods, ladies, and just get over it. I think
that Jeffrey Shank and marthama Clintic were actually friends, and
he actually wanted it to work out really well, but

(13:17):
once he did this research, he was like, I can't
can't support It's like, Martha, Martha, I'm sorry, Martha. I tried,
but Martha, you are wrong. Because here's here's what they do. First. First,
they do the experiment because they want to do a bigger,
better study. So they use a hundred and eighty six
Chinese women living in dorms over the course of a year,
and again you get this great layout of like the
dorm and what it's like there and whose friends with who,

(13:40):
who likes whom, who's around who's around each other a lot?
And uh So they do that and instead of just
asking a women to recall, they have the women keep journals,
which I have to say already that sounds like a
much better methodology than just getting someone to recall their
last two period start, right, Because when I think about
the last time you went to the doctor and they
were like, well, what was the date of your last period?

(14:01):
You have to scratch your head for a minute, you know,
I mean, we don't. Yeah, it can be hard to remember,
that's the point. So these women are in college, they're
keeping track of their um their period start dates. They're
all college age, and so they collect the data and
they run it through all sorts of all sorts of
data analyzes and they find, you know, yeah, sometimes you do.

(14:23):
You do start your period on the same day. Sometimes
you do see evidence of the fact that women might
be changing their cycles. But that's just because women change
their cycles. It's because there's not a set cycle length.
It can be affected by things such stress, It can
be affected by you know, diet, yeah, all these things.
So let's not let's not say that if these other
women causing this, because they really can't find anything other

(14:46):
than casual association. Right. Basically, when you take a large
group of women who are you know, sharing the same
space at some point, like you said there, they'll have
their period at the same time just by a chance,
and other times they won't, you know. And so that's
what they say. And they go back and they look
at all of the Clintic's work and they're like, this

(15:08):
is this is chance? So I guess doesn't It doesn't
diminish the amount of bonding you can do, can be more.
Instead of being like, oh, we're bonding because we're staying
so much time together, it's like, wow, we have the
good fortune to both have had our menstrual cycle at
the same time. But it's nothing more than that. Just chance,
just just chance. All the chance doesn't mean that we
have to be friendlier in the hall. Um, let's let's

(15:29):
not let's not take this too seriously. We don't need
to get married. I'd like to keep a casual distance
from you. But but you know, I think that the
reason why you said earlier in the podcast, of women
believe that they do synchronize with their girl friends, and
I think it's just because it's sort of just reflects
the findings of the Shank study that at some point

(15:52):
you have so many periods throughout your lifetime, and they're
probably so many times you know that it just slips
out somehow to a girlfriend or whoever that you are
experiencing your moon cycle, that at some point, you know,
the chances are the odds are in your favor that
at some point someone's gonna say me too exactly, and

(16:15):
you know there's and they still don't know. You know.
In the first nineteen se staid a clinic didn't even
rule out people who are on hormonal birth control because
she thought maybe they're still sending out the signals. Maybe
everyone was getting sink to the birth control person. I
can't prove it. There's it doesn't matter if you're on
birth control, if you're not. If you have ten periods
a year, twelve pairs a year, and have a main

(16:37):
periods you have, it's just chance. And I gotta say
it was I was a little sad to see them
clinic effect debunked. But at the same time too, Like
you said, Molly, it is an argument, uh against forging
false friendships on the basis of your periods. It's a
positive thing, true, And I feel like, you know, maybe

(17:00):
you have something in common with your enemy just because
you don't spend a lot of time with her, you
might still both be having a period. Yeah, just by chance.
Just by chance. The world spends on chance. So there
you have it, myth busted. Do women sync up their periods? Yeah? Maybe,
but it's just by happenstance, not because of the rainbow

(17:24):
bond of friendship between you and stars and magic. And
the jury is still out on pheromones. I mean, there
might still be something to that. But and if you
feel like your libidos take a little bit of a
dip fin hang out with some women who are breastfeeding,
that's another takeaway. Yeah, I think I think the takeaways
the McClintic is still doing pretty valuable work that, as
I mentioned, highlights women and the messages we might send

(17:46):
to each other in a really unique way. But the
question of the day to gallop how sync up? No busted.
So on that note, let's read some emals. I have
an email from Amelia on the episode about gender and instruments.

(18:08):
She writes, my father has been after me and my
two sisters for as long as I can remember to
play one very specific instrument, the susaphone. Not about an
instrument that came up in our podcast, she writes, Uh,
the susa phone is basically a giant tube, but that
wraps around the player's body A boy instrument, to be sure,
But Dad insisted, think about it. Your average Big ten

(18:30):
university needs twelve susophones on the field at every football game.
That means they need to bring in at least four
or five susophone players with every incoming freshman class. To
admissions officers who must know about these quotas, there could
be nothing more rare and desirable than a girl who
plays the susaphone. That must be the holy grail of admissions, diversity, scholarships,
and admissions courting abound. Dad never missed an opportunity to

(18:51):
point out the susaphone at parades and football games. He
would count them while listening to music. He always an
ear out for one, and as I approached college age.
He desperately bribed me to learn to play this instrument.
He figured there were only three buttons, it couldn't be
that hard. Well I never did learn to play it,
and neither have you. There my sisters. My sister and
I got into and graduated from college just fine without

(19:12):
the susophone. And I'm sure our youngest sister will. I
thought you might like to hear about a parent pressing
his daughters to break with those rigid gender roles, even
if it was for a break in tuition prices instead
of social change. Our musical greatness, and Amelia, it does
sound like we have very very similar fathers. And I'm
lucky that my father, I don't think, knows what a superphone. Um, well,

(19:34):
I've got one here from a listener in response to
an owner podcast on what constitutes an eating disorder, and
she says, I used to be a binge eater and
have now been struggling with bulimia for almost two years,
although I've avoided actually calling it that up until now.
I'm currently seeking help and getting better slowly, but surely.
I was so glad that you talked about the shame

(19:56):
involved in bolimia and other eating disorders, because that's exact
actually what it is. As someone who's been struggling with
an eating disorder, I would just like to say that
the best thing anyone can do who has a friend
that they're worried about is just be there for that person.
Like you both pointed out, there are a whole slew
of issues which underlie any eating disorder, issues surrounding control,
self image, perfectionism, et cetera. Some people are less responsive

(20:20):
to confrontation than others, but often saying that someone actually
cares about you and it's concerned for your well being
is very nice. I'm not saying that that alone will
solve all the problems that someone with eating disorders has,
but dealing with an eating disorder is a very solitary thing.
In my experience, You tend to isolate yourself, and having
someone to talk to you can help ease the feeling
of isolation. At the same time, as you to point

(20:41):
it out, no one should feel that they have to
play therapist for their friend, but the person is willing,
it can be very helpful just to support them in
the process of finding help. Admitting that you have an
eating disorder at all is very difficult. And shameful, and
finding help can be even more overwhelming. So thank you
so much from UH for the advice from someone who knows.

(21:01):
And if you would like to contact us, It's Mom
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and it's at how stuff works dot com for more

(21:23):
on this and thousands of other topics. Because it how
stuff works dot com. Want more how stuff works, check
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