Endometriosis occurs when cells from the lining of your womb (uterus) grow in other areas of your body. This can cause pain, heavy bleeding, bleeding between periods, and problems getting pregnant (infertility).

Alternative Names
Pelvic pain - endometriosis; Endometrioma
Causes
Every month, a woman's ovaries produce hormones that tell the cells lining the uterus to swell and get thicker. Your uterus sheds these cells along with blood and tissue through your vagina when you have your period.
Endometriosis occurs when these cells grow outside the uterus in other parts of your body. This tissue may attach on your:
- Ovaries
- Bowel
- Rectum
- Bladder
- Lining of your pelvic area
It can grow in other areas of the body, too.
These growths stay in your body, they do not shed when you have your period. But, like the cells in your uterus, these growths react to the hormones from your ovaries. They grow and bleed when you get your period. Over time, the growths may add more tissue and blood. The buildup of blood and tissue in your body leads to pain and other symptoms.
No one knows what causes endometriosis. One idea is that when you get your period, the cells may travel backwards through the fallopian tubes into the pelvis. Once there, the cells attach and grow. However, this backward period flow occurs in many women. Researchers think that the immune system in women with endometriosis may cause the condition.
Endometriosis is common. Sometimes, it may run in families. Endometriosis probably starts when a woman begins having periods. However, it usually is not diagnosed until ages 25 to 35.
You are more likely to develop endometriosis if you:
- Have a mother or sister with endometriosis
- Started your period at a young age
- Never had children
- Have frequent periods, or they last 7 or more days
- Have a closed hymen, which blocks the flow of menstrual blood during the period