A woman is born with a finite number of eggs, which are stored in the ovaries. The ovaries also make the hormones estrogen and progesterone, which control menstruation and ovulation. Menopause happens when the ovaries no longer release an egg every month and menstruation stops.
Menopause is considered a normal part of aging when it happens after the age of 40. But some women can go through menopause early, either as a result of surgery, such as hysterectomy, or damage to the ovaries, such as from chemotherapy. Menopause that happens before 40, regardless of the cause, is called premature menopause.