Endometriosis is a painful, chronic disease that affects 1 in 10 women and girls. It occurs when tissue like that which lines the uterus (called the endometrium) is found outside the uterus (womb) -- usually in the abdomen on the ovaries, the fallopian tubes and ligaments that support the uterus. It can also be found in the pelvic cavity.

Other sites for endometrial growths include the bladder, bowel, vagina, cervix, vulva and in abdominal surgical scars. Less commonly endometriosis can be found on the arm, leg, lungs, brain and other sites.

This misplaced tissue develops into growths or lesions which respond to the menstrual cycle in the same way in the same way that the tissue of the uterine lining does: each month the tissue builds up, breaks down and sheds.

While menstrual blood flows from the uterus and out of the body through the vagina, the blood and tissue shed from endometrial growth have no way of leaving the body. This causes internal bleeding, breakdown of the blood and tissue from the lesions and inflammation, and can cause pain, infertility, scar tissue formation, adhesions and bowel problems.