synchronised periods

[karly]

Why do women's periods synchronize when they live together.

[gem]

I don't know exactly, but it happens without fail. A natural phenomenon. Men's facial hair also grows slower when there are no women around, apparently.

[WaldoMcFroog]

Since difference hormones are subconsciously detectable through smell etc, if one woman is ovulating, and another who isn't is in close contact, the smell of the first woman's hormones will fool the other body into thinking that it should also be ovulating, and therefore, it will start kicking into the process earlier than it would naturally... Over time they synchronise.

[5029]

Its to do with the smell of the pheramones that are excreted through the armpits. Otherwise the above answer is correct

[WaldoMcFroog]

I stand corrected 5029! :-)