To be physically, emotionally, and mentally healthy, a woman needs to be exposed to cyclical, normal levels of both estradiol and progesterone for 30 to 45 years of her menstruating life span. The consequence of these cyclic ovarian hormone levels is approximately monthly vaginal bleeding during which the endometrium (lining of the uterus) is shed. This is called menstruation, or a period. A menstrual cycle is normally 21 to 35 days long, including the first day of flow until the day before the next cycle begins. Humans are rather unique among female mammals in having obvious cyclical vaginal bleeding. Human cultures, however, have generally negative views about menstruation; this negativity is projected onto the half of all humans who intermittently, normally bleed. Currently, both men’s ...

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