The cause of menopause is a natural decline in the levels of the female sex hormones estrogen and progesterone produced by the ovaries. Levels of these hormones increase and decrease regularly with the menstrual cycle during the fertile years, but as women reach their late 30s, the levels no longer rise as much as they once did. At this age, fewer potential eggs are ripening in your ovaries each month, and ovulation becomes less predictable.

The decline in hormone levels becomes more pronounced in the 40s. This is also the point when many women start to develop obvious symptoms including significant changes in the menstrual pattern and for some women, the other familiar signs of menopause (hot flashes, changes in mood, vaginal dryness, etc.). Over time, the ovaries produce less and less estrogen and progesterone until they shut down and you have no more periods. Usually there is a gradual tapering off of periods until they stop entirely.

Why do some women have severe symptoms while others may experience no bothersome symptoms at all? This is unclear, though it may have something to do with how fast the decline in hormone levels is; when the decline occurs faster, it may bring on more severe symptoms.

Researchers are also unsure of why there is such a wide variability in the age at which women reach menopause. While the average age is 51 for women in United States, the normal range is between 45-55 and natural menopause can occur as early as 35 or as late as 60. The difference may have something to do with the number of prospective eggs that each woman is born with: those with fewer eggs may start menopause earlier.

In addition to natural menopause, the cessation of periods can also occur due to surgical intervention. If a woman has her uterus removed, all menstruation will stop because there is no longer any uterine lining to shed each month. However, if the ovaries are left behind (a partial hysterectomy), the monthly cycle of hormone changes will continue until the levels of these hormones declines naturally and menopause occurs (often a little earlier than normal). If the ovaries are removed along with the uterus (total hysterectomy) it is called “surgical menopause” because without the ovaries, the body produces very little estrogen and progesterone and so menopause occurs immediately. The symptoms of surgical menopause can be more severe than natural menopause because instead of the hormone levels gradually declining, they plummet literally overnight.