Risk Factors

Endometriosis affects at least 5.5 million women in North America and millions more worldwide. An estimated 2% to 4% of all premenopausal adult women have detectable endometriosis, and over a third of these women experience noticeable pain. Because many women with endometriosis have no symptoms, the actual percentage of premenopausal women with the disorder may be as high as 15%. Some experts believe endometriosis may be responsible for between 45% and 70% of chronic menstrual pain in adolescence.

Age. Endometriosis can occur in women of all ages. It has been reported in girls as young as 8 (and has been documented before the onset of menstruation), and in women over 75, with the average age being between 25 and 29. Approximately 40% to 60% of women with endometriosis report symptoms before age 25.

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Ethnic Groups. Among the major ethnic groups it appears to be most common among Asian women, with Caucasians next. It is reported least frequently in African American women.

Greater Exposure to Menstruation

Women at higher risk for endometriosis tend to have greater exposure to menstruation. Those at higher risk have a shorter than normal cycle, heavier periods, and longer periods. Heavier, more frequent periods, or longer exposure may simply make the risk for retrograde menstruation more likely. (This is the condition in which menstrual flows backward and is believed to be at least partially responsible for the initial development of endometriosis.) Menopause usually brings an end to mild to moderate endometriosis, although if women with a history of endometriosis take hormone replacement therapy (HRT), the condition may be reactivated.

Not Having Children