Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Endometriosis

What Is It?

Endometrial tissue lines the inside of the uterus. In endometriosis, this tissue grows outside of the uterus.

Endometriosis may develop in the:

• Ovaries

• Outside surface of the uterus

• Pelvis and lower abdomen

• Fallopian tubes

• Spaces between the bladder, uterus and rectum

• Wall of the rectum, bladder, intestines or appendix (less commonly)

• Lung, arm, thigh and skin. (This is rare.)

Misplaced endometrial tissue behaves like endometrial tissue in the uterus. It responds to the monthly rise and fall of female hormones. It also can ooze blood during menstruation. This can cause pelvic or abdominal pain.

As misplaced endometrial tissue grows, it can interfere with a woman's fertility. It may cover or grow into the ovaries. Or it may distort or block the fallopian tubes.

Endometrial tissue on the ovaries may form into large fluid-filled cysts. These are called endometriomas.

A woman may have an increased risk of endometriosis if:

• She has a heavy menstrual flow.

• She has a short menstrual cycle (27 days or less).

• She has a close female relative with endometriosis.

A woman's risk is probably lower than average if:

• She is slightly underweight.

• She exercises regularly.

• She has had multiple pregnancies.

• She has used oral contraceptives.