What causes menopause?

A woman is born with a finite number of eggs, which are stored in the ovaries. The ovaries also produce the hormones estrogen and progesterone, which regulate menstruation and ovulation. Menopause occurs when the ovaries are totally depleted of eggs and no amount of stimulation from the regulating hormones can force them to work.

Menopause occurs when a woman's ovaries run out of functioning eggs. At the time of birth, most females have about 1-3 million eggs, which are gradually lost throughout a woman's life. By the time of a girl's first menstrual period, she has an average of about 400,000 eggs. By the time of menopause, a woman may have fewer than 10,000. A small percentage of these eggs is lost through normal ovulation (the monthly cycle). Most die off through a process called atresia, which is not well understood.

Menopause, when it occurs between the ages of 45 and 55, is considered "natural" and is a normal part of aging. But, some women can experience menopause early, either as a result of a surgical intervention, such as hysterectomy, or damage to the ovaries, such as from chemotherapy. Menopause that occurs before the age of 45, regardless of the cause, is called premature menopause.

Normally, ovulation is triggered by a hormone called FSH, or follicle-stimulating hormone. As you approach menopause, your remaining eggs become more resistant to FSH, and your ovaries dramatically reduce their production of a hormone called estrogen. Estrogen has effects on a variety of body organs, including the blood vessels, heart, bone, breasts, uterus, urinary system, skin, and brain. Loss of estrogen is believed to be the cause of many of the symptoms associated with menopause.

At the time of menopause, the ovaries also may decrease their production of testosterone—a hormone involved in your libido, or sexual drive.