No one knows for sure what causes this disease. Researchers are studying possible causes:
- Problems with menstrual period flow. Retrograde menstrual flow is the most likely cause of endometriosis. Some of the tissue shed during the period flows through the fallopian tube into other areas of the body, such as the pelvis.
- Genetic factors. Because endometriosis runs in families, it may be inherited in the genes.
- Immune system problems. A faulty immune system may fail to find and destroy or overreact to endometrial tissue growing outside of the uterus. Immune system disorders and certain cancers are more common in women with endometriosis.
- Hormones. The hormone estrogen appears to promote endometriosis. Research is looking at whether endometriosis is a problem with the body's hormone system.
- Surgery. During a surgery to the abdominal area, such as a Cesarean (C-section) or hysterectomy, endometrial tissue could be picked up and moved by mistake. For instance, endometrial tissue has been found in abdominal scars.