13. Science still doesn’t know whether it’s true that women who live together wind up synchronizing their periods.
Although many women swear that they always wind up having their periods around the same time as their close friends, science has yet to definitively answer whether this legend is true.
14. Menstrual discharge contains more than blood.
It also contains shedded uterine tissue, which gives it a thicker and gummier consistency than blood alone.
15. Your period can also change your voice.
One study published in the journal Ethology claimed that men who listened to recordings of women’s voices were generally able to tell which women were menstruating. One would assume that their tone while menstruating was slightly more menacing than normal.
16. You can still get pregnant on your period.
It’s unlikely, but still possible, since sperm can stay alive inside the vagina for up to a week. The risk of pregnancy is highest when having sex during the end of one’s menstrual cycle.
17. If you’re bleeding, that may be a sign of pregnancy rather than menstruation.
Just because you’re bleeding doesn’t mean it’s your period. During the early stages of pregnancy, women may experience light blood flow or spotting due to a process known as “implantation bleeding.”
18. Your body mimics the symptoms of pregnancy in the days leading up to your period.
In the days leading up to when Aunt Flo knocks on the door, your body secretes hormones that cause irritability, feeling bloated, acne, and fluid retention—which are precisely the same symptoms one experiences during pregnancy.
19. Human females are one of the only mammals that go through menopause.
The other two breeds are elephants and humpback whales.
20. PMS can make you more violent.
One study of female prison inmates concluded that they are far more likely to commit violent acts in the days preceding menstruation than in the days directly after menstruation.
21. You may think more like a male while you’re menstruating.
Lowered estrogen levels during menstruation may actually enhance a woman’s “male cognitive skills,” lending a temporary cognitive advantage in areas such as spatial thinking.
22. Your period can cause an iron deficiency.
Losing all that blood means losing all that iron. You may also feel so rotten and fatigued, you don’t bother ironing your clothes.
23. You need a little bit of body fat in order to menstruate.
If your body fat plummets below 8-12%, your period will abruptly cease, if it ever began at all. Fat cells are correlated with a woman’s estrogen levels and are thus necessary in both menstruation and procreation.
24. Menstrual symptoms lead to 100 million lost work hours in America yearly.
It’s a legitimate medical excuse, one that men are never able to claim.
25. While menstruating, you may bleed from places other than your vagina.
In a very rare medical condition known as “vicarious menstruation,” women on their period may also harmlessly bleed from their mouth, ears, lungs, nose, eyes, and skin. It is not known exactly why this happens, only that it does. 
