Most women who suffer from endometriosis will tell you the pain is intense. It’s a chronic condition affecting millions throughout the world. Endometriosis varies from woman to woman. Some don’t know they have it until they see a doctor about infertility. Some have mild cramping which seems normal. In others, the pain and bleeding are so bad they can’t work or attend school.

Endometriosis is a condition in which tissue – behaving like tissue lining the uterus during a menstrual period – grows in other areas of the body. This tissue thickens, breaks down and bleeds each month. But it’s outside the uterus leaving nowhere for it to exit the body. It can become trapped, irritate surrounding tissue and even bind organs together.

This growth can occur in the pelvic area, on the ovaries, vagina, cervix, vulva, bowel, rectum and bladder. It can also grow in abdominal surgical scars. Less common areas include lungs, arms and thighs.

The exact cause of endometriosis is unknown, but experts do know estrogen makes it worse. High levels of estrogen are most prominent during childbearing years. That’s why women with endometriosis tend to have it from their teens into their 40s.

There are several theories as to what causes endometriosis. One suggests all women experience some menstrual tissue backup, but an immune system or hormonal problem allows endometriosis to develop in some women. Another suggests endometrial tissue is distributed through the lymph or blood system. A genetic theory says it’s in certain families’ genes.

Regardless of the theories, there are very real symptoms of endometriosis. A common one is pain. Where it hurts depends on where the misplaced tissue is growing. Some experience pain in the lower abdomen, the rectum or vagina, or lower back. It may happen before and during a menstrual period or all the time. Some women have more pain during sex, when they have a bowel movement, or during ovulation.

Another symptom is abnormal bleeding like heavy periods, spotting or bleeding between periods, bleeding after sex, or blood in urine or stool. In other cases, the only symptom is trouble getting pregnant.

There is no cure for endometriosis, but there are treatments. For pain and bleeding, there is medication or surgery. Women hoping to get pregnant may need surgery to remove the misplaced tissue.

A more extreme measure to end severe pain is to remove the uterus and ovaries. One thing to consider, endometriosis usually stops causing problems when periods stop.

Stacy Lloyd is a writer and video producer in Phoenix, Arizona. A former television news journalist, she covered stories around the world. Currently, she produces corporate and non-profit videos and broadcast programming.