What is Endometriosis?

Your uterus is lined with a type of tissue called endometrium. Each month, your body releases hormones that cause the endometrium to thicken and get ready for an egg. If you get pregnant, the fertilized egg attaches to the endometrium and starts to grow. If you do not get pregnant, the endometrium breaks down, and your body sheds it as blood. This is known as your menstrual period.

When you have endometriosis, the implants of tissue outside your uterus act just like the tissue lining your uterus. During your menstrual cycle, they get thicker, then break down and bleed. But the implants are outside your uterus, so the blood cannot flow out of your body. The implants can get irritated and painful. Sometimes they form scar tissue or fluid-filled sacs (cysts). Scar tissue may make it hard to get pregnant.

With each menstrual cycle, the implants go through the same growing, breaking down, and bleeding that the uterine lining (endometrium) goes through. This is why endometriosis pain may start as mild discomfort a few days before the menstrual period and then usually is gone by the time the period ends. But if an implant grows in a sensitive area, it can cause constant pain or pain during certain activities, such as sex, exercise or bowel movements.

Some women have no symptoms or problems. Others have mild to severe symptoms or infertility. There is no way to predict whether endometriosis will get worse, will improve, or will stay the same until menopause.