Oxford Women's Health
The endometrium is the name of the tissue that lines your uterus (womb). Endometriosis is a condition where tissue, like the endometrium, grows in other parts of the body. Usually these growths occur inside the pelvic cavity in places such as the ovaries, bowel, or a lining of the pelvic cavity and abdomen called the peritoneum. Each month, as the endometrial lining of the uterus builds up with blood that will be lost during your period, these other growths of endometrial tissue get bigger and can bleed and cause inflammation and adhesions (internal scarring).
Some women with this condition do not have many symptoms, whereas others suffer severe pain and problems such as infertility and tiredness.
Treatment includes medication that will help control the pain and inflammation, and some women may need surgery to remove the tissue growths.