Endometrial tissue outside of the uterus responds to your monthly hormone cycle, just like the tissues inside your uterus. During your menstrual cycle, endometrial tissue swells with blood, which can irritate other tissues nearby and may cause scar tissue to form. In turn, the scar tissue can form abnormal connections between organs.

The symptoms of endometriosis include cyclic pain and cramps. Pain may occur during sexual intercourse or during bowel movements, depending on where the endometrial tissue has grown. Lower back, intestinal, and pelvic pain may occur as well. Endometriosis can also reduce a woman's chances of becoming pregnant. In fact, endometriosis is a common cause of infertility.