Endometriosis (en-doe-me-tree-O-sis) is an often-painful condition in which tissue that is similar to the inner lining of the uterus grows outside the uterus. It often affects the ovaries, fallopian tubes and the tissue lining the pelvis. Rarely, endometriosis growths may be found beyond the area where pelvic organs are located.

Endometriosis tissue acts as the lining inside the uterus would — it thickens, breaks down and bleeds with each menstrual cycle. But it grows in places where it doesn't belong, and it doesn't leave the body. When endometriosis involves the ovaries, cysts called endometriomas may form. Surrounding tissue can become irritated and form scar tissue. Bands of fibrous tissue called adhesions also may form. These can cause pelvic tissues and organs to stick to each other.

Endometriosis can cause pain, especially during menstrual periods. Fertility problems also may develop. But treatments can help you take charge of the condition and its complications.


The main symptom of endometriosis is pelvic pain. It's often linked with menstrual periods. Although many people have cramping during their periods, those with endometriosis often describe menstrual pain that's far worse than usual. The pain also may become worse over time.

Common symptoms of endometriosis include:

  • Painful periods. Pelvic pain and cramping may start before a menstrual period and last for days into it. You also may have lower back and stomach pain. Another name for painful periods is dysmenorrhea.
  • Pain with sex. Pain during or after sex is common with endometriosis.
  • Pain with bowel movements or urination. You're most likely to have these symptoms before or during a menstrual period.
  • Excessive bleeding. Sometimes, you may have heavy menstrual periods or bleeding between periods.
  • Infertility. For some people, endometriosis is first found during tests for infertility treatment.
  • Other symptoms. You may have fatigue, diarrhea, constipation, bloating or nausea. These symptoms are more common before or during menstrual periods.

The seriousness of your pain may not be a sign of the number or extent of endometriosis growths in your body. You could have a small amount of tissue with bad pain. Or you could have lots of endometriosis tissue with little or no pain.

Still, some people with endometriosis have no symptoms. Often, they find out they have the condition when they can't get pregnant or after they get surgery for another reason.

For those with symptoms, endometriosis sometimes may seem like other conditions that can cause pelvic pain. These include pelvic inflammatory disease or ovarian cysts. Or it may be confused with irritable bowel syndrome (IBS), which causes bouts of diarrhea, constipation and stomach cramps. IBS also can happen along with endometriosis. This makes it harder for your health care team to find the exact cause of your symptoms.

When to see a doctor

See a member of your health care team if you think you might have symptoms of endometriosis.

Endometriosis can be a challenge to manage. You may be better able to take charge of the symptoms if:

  • Your care team finds the disease sooner rather than later.
  • You learn as much as you can about endometriosis.
  • You get treatment from a team of health care professionals from different medical fields, if needed.


The exact cause of endometriosis isn't clear. But some possible causes include:

  • Retrograde menstruation. This is when menstrual blood flows back through the fallopian tubes and into the pelvic cavity instead of out of the body. The blood contains endometrial cells from the inner lining of the uterus. These cells may stick to the pelvic walls and surfaces of pelvic organs. There, they might grow and continue to thicken and bleed over the course of each menstrual cycle.
  • Transformed peritoneal cells. Experts suggest that hormones or immune factors might help transform cells that line the inner side of the abdomen, called peritoneal cells, into cells that are like those that line the inside of the uterus.
  • Embryonic cell changes. Hormones such as estrogen may transform embryonic cells — cells in the earliest stages of development — into endometrial-like cell growths during puberty.
  • Surgical scar complication. Endometrial cells may attach to scar tissue from a cut made during surgery to the stomach area, such as a C-section.
  • Endometrial cell transport. The blood vessels or tissue fluid system may move endometrial cells to other parts of the body.
  • Immune system condition. A problem with the immune system may make the body unable to recognize and destroy endometriosis tissue.

Risk factors

Factors that raise the risk of endometriosis include:

  • Never giving birth.
  • Starting your period at an early age.
  • Going through menopause at an older age.
  • Short menstrual cycles — for instance, less than 27 days.
  • Heavy menstrual periods that last longer than seven days.
  • Having higher levels of estrogen in your body or a greater lifetime exposure to estrogen your body produces.
  • Low body mass index.
  • One or more relatives with endometriosis, such as a mother, aunt or sister.

Any health condition that prevents blood from flowing out of the body during menstrual periods also can be an endometriosis risk factor. So can conditions of the reproductive tract.

Endometriosis symptoms often happen years after menstruation starts. The symptoms may get better for a time with pregnancy. Pain may become milder over time with menopause, unless you take estrogen therapy.



The main complication of endometriosis is trouble getting pregnant, also called infertility. Up to half of people with endometriosis have a hard time conceiving.

For pregnancy to happen, an egg must be released from an ovary. Then the egg has to travel through the fallopian tube and become fertilized by a sperm cell. The fertilized egg then needs to attach itself to the wall of the uterus to start developing. Endometriosis may block the tube and keep the egg and sperm from uniting. But the condition also seems to affect fertility in less-direct ways. For instance, it may damage the sperm or egg.

Even so, many with mild to moderate endometriosis can still conceive and carry a pregnancy to term. Health care professionals sometimes advise those with endometriosis not to delay having children. That's because the condition may become worse with time.


Some studies suggest that endometriosis raises the risk of ovarian cancer. But the overall lifetime risk of ovarian cancer is low to begin with. And it stays fairly low in people with endometriosis. Although rare, another type of cancer called endometriosis-associated adenocarcinoma can happen later in life in those who've had endometriosis.