Endometriosis is a chronic condition in which tissue that is similar to the lining of the uterus (endometrium) grows outside the uterus. This tissue can attach to organs such as the ovaries, fallopian tubes, bladder, bowel, the lining of the pelvis, and, in rare cases, other parts of the body.

Even though it’s outside the uterus, this tissue can still respond to hormonal changes during the menstrual cycle. That can lead to inflammation, swelling, irritation, scar tissue (adhesions), and significant pain.