If you've ever lived with other women, and none of you were on hormonal birth control, you may have discovered that your cycles slowly began to mimic each others. This is called menstrual synchrony, but many scientists will say that women who live together, menstruate together is hogwash. I've actually experienced this so there's got to be some truth to it.
In 1971, Martha McClintock studied 135 college women. She wrote down the starting date of their periods at three different times during the year. She discovered that women who lived in close-knit groups had their periods an average of 6 to 4 days apart during certain times of the year. It's said to be caused by pheromones, the release of chemical signals that influence behavior and physiology among people. Other studies conducted after this, however, showed no connection between women living together and their cycles synchronizing.
What do you think about menstrual synchrony? Have you ever lived with a woman (sister, mother, roommate) or group of women and noticed that you had your periods about the same time?
Yves Saint Laurent
I've always noticed this happens! There was about two years when my mom and I did this (she had a hysterectomy when I was in junior high, though). Later on in high school, my best friends that I hung out with every day all started to more or less have our periods at the same time. And freshman year of college, our whole floor minus the girls on the pill did! I think it has to be true.
1what's not to believe? it definitely happens.
martha mcclintock is a professor at my school! she's a really interesting lecturer!
2totally happens in my office. Between the 1st and the 10th of the month, all of us in accounting and the reception area are in full swing. This kind of helps me keep track of my cycle. It makes me laugh, cuz once my coworker starts, we're all like "damn! the curse is back!"
3Definitely. In college, my entire floor had synchronized periods for a while - it was so funny yet so NOT funny.
4I'm a believer!
5yes i've noticed this happening with some of my closest friends,but we dont live together,just hang out
6I experienced this with a close friend of mine and we didn't even live together
7I have experienced it numerous times. Strange but true!
8I work with a girl who obviously has some potent pheromones, because I used to have highly irregular periods until I started working here. Now, I have them every d*mn month, right on time with hers, save a day or two sometimes. So, yeah. I definitely believe it.
9for sure. my girls and i in high school all had ours within a week or so. even our volleyball team was synchronized. it was....interesting...to say the least!
10but then in college, my roommate and i were both on the pill, so that changed.
My best friend and I always noticed that if either one of us was a day or two late, and say I had started and she was late and then we hung out, she started the next day! We use to be about 2 weeks apart and now we are MAYBE one day apart at the longest. I was the same way with my sister when her and I still lived with our parents
11I lived in a quad for a semester, and by the last month we became screaming b*tches during the same week!
12I totally believe this happens; it happened every year in college with my roommates and me! This is such a strange phenomenon. I wonder which girl's pheromones or hormones are the more dominant ones that the other girl synchronizes up with!
13I totally believe this really happens. Ive lived in a college dorm with all girls, and Ive also lived in a house with 4 other girls. Always the first few months my period is totally whack...lasting too long, or being too early or too late. Then after 2 or 3 months is slowly falls into place with the other girls who Im living with. Its really not very fun to have 4 girls living in the same house when you are all on your period at the same time.
14shanimal-I think they just syncronize each other. When I was living with my female roommates there was one month, where we had a new roommate come in and she totally through us all off our cycles, so we were talking about. We came to the conclusion that anytime there is a disturbance (like a new roommy moving in) we all get out of sync, then slowly fall back into place with eachother.
15Definitely! This has happened with my friends back in the States, and now again with my girls in the UK - because in either place I spend loads of time with them.
16YES. SO strange. It's like what everyone else said, all the girls in my freshman dorm started at the same time.
17true.
18yup..when i was still living at home, my mom, my sister and i all got our periods within days of each other. my sister first though, so i was always prepared
19Believe in it?? I thought it was scientifically PROVEN?
20Even though I'm in school for Biomedical Science, I can say that scientists don't know everything.
Seriously, all you have to do is have more than one woman in a house or even a classroom! environment to see the differences. Since I started classes in September, my cycle hasn't been right. When I was in boarding school, there were so many scares about pregnancy, because a lot of us had never heard of this phenomenon - even girls (like me) who had never had sex were worried (which was a bit sad).
This same thing happens in the wild (think lions, etc), so no one should be at all surprised that it happens with people, too.
21hmm.. well all of us are unanimous... i wonder how come it doesn't show up in the studies though???
22yes actually with a few girls i used to work with
23my mum and I always have it in within the same week, so I totally believe it.
24When I was a teenager, my mother, sister, and I almost always started ours within a week or so of each other, and in college I always lived on smallish all-girls floors. At the start of the year, there'd be a steady supply of discarded pads and tampons in the trashcans all month, but by the end there'd be a few here and there from girls on the Pill and then BOOM! all the rest of us would go at once.
So yeah, you could say I'm a believer.
25I used to live in a dorm with 20 other women and this totally happened. My phermones must not have been too strong though, because my cycle always seemed to follow everyone elses.
26This is so true. The girls I'm around daily are all on the same track as I am :]
27So true... it has to do with pheromones and other bodily chemicals in the air and such, which affects us because of close proximity. My roommate was on the pill and my cycle synced up to hers! It was kinda weird. =P
28It's funny but I do. In my household when I was still single, I lived with my family--my sister, and 2 other girl roommates and we all have periods almost at the same time, if not, in time order. Me first, then next my sister and then so on. It also happened when I was in college living with 3 other female roommates and we definitely have periods one after the other.
29This totally happens!
30Yes, it's creepy. This happened among my close girlfriends, too, and we didn't live together. We were just close friends. Weird!
31I thought it was a fact that this happens.
32Hm, I actually do NOT believe this...or maybe my two sisters, my mom, cousin and aunt are just immune
33
All those scientists studying were probably all males! They would know!... 
34This always happens to me, my 2 sisters and mom... my poor father!
35freaky but true. we r miraculous creatures...
36this is definitely true! the benefits of it happening - you can all be b*tchy and crampy together! the downside (especially if sharing a bathroom in a dorm) - you will soon run out of tampons~!
37I definitely believe it! My daughter and I start at the same time.
38This is so true. It happened in every office I worked in.
39Seriously.. what's not to believe? I definitely believe this is true. My roommate and I got our periods within an hour of each other just the other day. In high school, all my basketball teammates got our periods within a week of each other. I never really got it the same time as my mother, but I probably spend more time with my roommate/teammates than my mother, so I definitely thing "menstrual synchrony" is real.
40Seriously.. what's not to believe? I definitely believe this is true. My roommate and I got our periods within an hour of each other just the other day. In high school, all my basketball teammates got our periods within a week of each other. I never really got it the same time as my mother, but I probably spend more time with my roommate/teammates than my mother, so I definitely thing "menstrual synchrony" is real.
41It's certainly true. Happened at home and in college. Also, I read somewhere that it was important to be synchronized way back in history because that way women were pregnant together (which helped with wet nurses, etc). Also, women in Biblical times went to a separate place during their periods... I believe they thought it was related to the moon cycles, but it would make sense if it was just the hormones!
42Firm believer in this! I went to an all girls boarding school and this was a frequent occurrence in the dorms!
43This is true- It's weird, but every month me and all the other girls on my floor in my dorm all cycle together. I remember the first week I arrived it seriously threw my body out of whack!
44My sister, best friend, and I are synced up. My sister and I live together and both have terrible PMS, so we try to go to opposite sides of the house.
45this happens with myself and all the girls in my workplace, we seem to take turns. it's like clockwork. It's kind of nice though that also we're so close, we kind of keep track of eachother so we'll know if something's wrong.
46i go to an all girls school and its so funny because everyone, i mean everyone in the entire school, is PMSing at the same time. its like i walk in in the morning and no ones talking to each other and everyone's just sitting around pouting haha, and you walk through teh hallways and hear people screaming for tampons. gotta love it!
47i didnt know people denied this happened...doesnt it happen in like every tribe in africa? where all teh women get together?
This happens to me all the time with different women.
48yes i'm a believer...my sisters,my mom and me we get it around the same time!!
49totally! my mom and i always had it together... Dad hated that week!
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