# co-habiting females - why do their periods coincide? **URL:** \ **Category:** Factual Questions\ **Created:** [November 10, 2001, 2:19am UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563 "2001-11-10T02:19:33Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Jojo](https://avatars.discourse-cdn.com/v4/letter/j/ecd19e/32.png) [@Jojo](https://boards.straightdope.com/u/Jojo)\ **Post date:** [November 10, 2001, 2:19am UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563/1 "2001-11-10T02:19:33Z")
emm…thats it. Why? Sorry if this is a dumb male question but I really don’t know why. Ive lived with groups of females in the past however and it does seem to happen. Are they more psychic or something? ---
**Author:** ![Gazoo](https://avatars.discourse-cdn.com/v4/letter/g/ce73a5/32.png) [@Gazoo](https://boards.straightdope.com/u/Gazoo)\ **Post date:** [November 10, 2001, 2:23am UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563/2 "2001-11-10T02:23:12Z")
[http://www.straightdope.com/classics/a2\_306.html](http://www.straightdope.com/classics/a2_306.html) ---
**Author:** ![Jojo](https://avatars.discourse-cdn.com/v4/letter/j/ecd19e/32.png) [@Jojo](https://boards.straightdope.com/u/Jojo)\ **Post date:** [November 10, 2001, 2:58am UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563/3 "2001-11-10T02:58:13Z")
Thanks for the link. So even Cecil thinks its a “complete mystery”. That doesn’t bode well. ---
**Author:** ![Zyada](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zyada/32/3028_2.png) [@Zyada](https://boards.straightdope.com/u/Zyada)\ **Post date:** [November 10, 2001, 3:23am UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563/4 "2001-11-10T03:23:42Z")
The “why” is still something of a mystery, however, the mechanism has been found: [Stinkin’ Synchin’](http://www.mum.org/Odor.htm#anchor49256) I’ve seen another study that found that pheremones released at one point in the menstrual cycle elongated the recipients cycle; and that other times the pheremones shortened the cycle. ---
**Author:** ![kniz](https://avatars.discourse-cdn.com/v4/letter/k/c37758/32.png) [@kniz](https://boards.straightdope.com/u/kniz)\ **Post date:** [November 10, 2001, 3:38am UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563/5 "2001-11-10T03:38:32Z")
I heard that in any group of females living together, that one was the dominant female and the other females would have periods to coincide with hers. For instance, daughters will synch with mother, and so forth. ---
**Author:** ![Guinastasia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/guinastasia/32/5751_2.png) [@Guinastasia](https://boards.straightdope.com/u/Guinastasia)\ **Post date:** [November 10, 2001, 3:59am UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563/6 "2001-11-10T03:59:25Z")
Hell, we didn’t even LIVE together, but my best friends and I would always get our periods around the same time. Maybe we should survey us female Dopers-see what times we get our periods? ---
**Author:** ![Cazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cazzle/32/75_2.png) [@Cazzle](https://boards.straightdope.com/u/Cazzle)\ **Post date:** [November 10, 2001, 4:03am UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563/7 "2001-11-10T04:03:53Z")
It’s never happened to me, in all the years I lived with my mother, or after when I shared with female friends. I guess it must happen to some, but not to all. ---
**Author:** ![Sweet\_Sota\_Girl](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@Sweet\_Sota\_Girl](https://boards.straightdope.com/u/Sweet_Sota_Girl)\ **Post date:** [November 10, 2001, 4:19am UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563/8 "2001-11-10T04:19:01Z")
> [@](#): > > \*Originally posted by Guinastasia \* > \*\*Hell, we didn’t even LIVE together, but my best friends and I would always get our periods around the same time. > Maybe we should survey us female Dopers-see what times we get our periods? \*\* You would also have to take into account those of us who are on birth control pills, and therefore have “fixed” periods. ---
**Author:** ![Guinastasia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/guinastasia/32/5751_2.png) [@Guinastasia](https://boards.straightdope.com/u/Guinastasia)\ **Post date:** [November 10, 2001, 3:05pm UTC](https://boards.straightdope.com/t/co-habiting-females-why-do-their-periods-coincide/92563/9 "2001-11-10T15:05:47Z")
I was teasing, actually.