Endometriosis (en-do-me-tree-O-sis) is a chronic (ongoing) condition in which pieces of the lining of the uterus (VOO-ter-us) become embedded in tissues outside the uterus.

What Is Endometriosis?

The endometrium (en-do-ME-tree-um) is the lining of the uterus, which is the muscular organ where a fetus * develops during pregnancy. Endometriosis is a condition in which endometrial tissue implants and grows outside the uterus. During the monthly menstrual cycle * , chemicals called hormones * cause the endometrium to grow thick in preparation for receiving a fertilized egg at the beginning of pregnancy. If the egg is not fertilized, there is no pregnancy and the endometrium is shed as blood and tissue during the monthly menstrual period.

In a woman with endometriosis, fragments of endometrial tissue develop outside the uterus. The cause of endometriosis is not fully understood. There are several theories. Some scientists think that some of the endometrial tissue that should leave the body during menstruation does not. Instead, these stray fragments find their way into other parts of the pelvic cavity. Here the stray pieces of tissue attach to other organs, such as the ovaries * or intestines * , stick organs together, or form scar tissue. Scientists theorize there may be a genetic predisposition (inherited tendency) toward developing endometriosis. Research ongoing as of 2015 seeks to determine whether stray tissues develop in some women because their immune system * , which normally destroys any unexpected material such as stray endometrium, does not function emciently. In addition, some scientists are exploring whether exposure to human-made chemicals found in the environment may trigger endometriosis in some women.

How Common Is Endometriosis?

According to the Endometriosis Association, estimates as of 2015 suggested that between 2 and 10 percent of women or 5.5 million women in North America had endometriosis.

The endometrium is the lining of the uterus. In women with endometriosis, fragments of endometrial tissue become attached to other organs outside the uterus.

The endometrium is the lining of the uterus. In women with endometriosis, fragments of endometrial tissue become attached to other organs outside the uterus. The symptoms of endometriosis may include heavy bleeding, abdominal pain, lower back pain, and tenderness and pain in the pelvic area.
Illustration by Frank Forney. © 2016 Cengage Learning®.

How Do Women Know They Have Endometriosis?

Endometrial implants or clumps of tissue outside the uterus respond to hormones in the same way as endometrial tissue inside the uterus: they grow, break down, and bleed. When endometrial tissue breaks down outside the uterus, it releases chemicals that irritate internal tissues and cause pain. Although some women with endometriosis do not have any symptoms, for others the symptoms of endometriosis include heavy bleeding during menstruation, abdominal and lower back pain, tenderness and pain in the pelvic area, diarrhea, constipation, and bleeding from the rectum * .

Endometriosis can develop in any woman who is menstruating, but it most often affects women who are between the ages of 25 years and 40 years. Endometriosis is one of the three major causes of female infertility (the inability to conceive a child) and accounts for 10 to 15 percent of all instances of female infertility. Endometriosis can keep women from becoming pregnant if stray endometrial tissue attaches to the ovaries and forms scar tissue that prevents the egg from leaving the ovary. Alternately, stray endometrial tissue can block the fallopian tubes * , which carry the egg from the ovaries to the uterus. Between 30 and 40 percent of women who have endometriosis have difficulty becoming pregnant.

How Do Doctors Diagnose and Treat Endometriosis?


Doctors may suspect that a woman has endometriosis based on her history of symptoms. Initially, a doctor may perform an ultrasound * or order magnetic resonance imaging * . These noninvasive tests use energy waves to produce a picture of the internal organs. However, to diagnose endometriosis definitively, a doctor uses a procedure called laparoscopy (lapa-ROS-ko-pee), in which a laparoscope (viewing instrument) is inserted into the abdomen or pelvic cavity through a small incision. This procedure allows the doctor to examine the abdominal or pelvic cavity for pieces of endometrium that may have become implanted on surfaces of the intestines, ovaries, and other places where they are likely to be found.


Endometriosis is treatable, but there is no cure for the condition. In mild cases, treatment may not be necessary. When treatment does become necessary, it can be complicated. The age of the woman, her general health, the severity of her condition, and whether she wants to have children must all be considered.

Hormone medications can suppress the development of endometrial tissue or cause the fragments to wither away, which may take as long as six months. Other medications may be prescribed to relieve pain. Sometimes surgery is needed to remove some of the abnormal tissue. Older women not planning to have more children may consider having a hysterectomy (his-ter-EK-to-mee) to help solve the problem. This surgery removes the uterus and sometimes other reproductive organs. Women who wish to have children and are having difficulty becoming pregnant should consult a doctor who is a fertility expert.

Can Endometriosis Be Prevented?

Endometriosis cannot be prevented. However, women may be able to lower their risks for developing the disorder by lowering the levels of the hormone estrogen in their bodies. Lowering estrogen levels may result from talking with a physician about the best uses for hormonal birth control, exercising regularly, and avoiding large amounts of alcohol, which raises estrogen levels in women.

Hormones and Endometriosis

Changing levels of hormones regulate the menstrual cycle. Estrogens, progesterone, and prostaglandins control the buildup and shedding of the endometrial lining of the uterus. Altering these hormone levels, either during pregnancy or by taking oral contraceptives (birth control pills), may help to relieve symptoms of endometriosis.

Many women with endometriosis are able to have children, and many are free of symptoms when they are pregnant. During pregnancy, the hormone balance that usually causes the monthly menstrual cycle changes. Instead of causing the endometrium to grow and then break down, different hormones work to make the lining of the uterus hospitable to the developing fetus. Therefore, the implants may be free of the hormonal effects that cause the symptoms of endometriosis.

Oral contraceptives are mixtures of reproductive hormones that, when taken every day, act to change the hormone balance in the body to prevent pregnancy. Side effects of oral contraceptives include reduced cramping and lighter menstrual periods. By altering the body's hormonal balance, they also may be effective in reducing the symptoms of endometriosis.

See also Infertility • Menstruation and Menstrual Disorders • Pregnancy


Books and Articles

Schrager, Sarina, Julianne Falleroni, and Jennifer Edgoose. “Evaluation and Treatment of Endometriosis.” American Family Physician 87, no. 2 (2013): 107–113.


End to Endo. “Endometriosis” End to Endo: Genetic Endometriosis Research Study. http://www.endtoendo.com/Endometriosis_Prevalence_End_to_Endometriosis.html (accessed October 13, 2015).

MedlinePlus. “Endometriosis.” U.S. National Library of Medicine. http://www.nlm.nih.gov/medlineplus/endometriosis.html (accessed October 13, 2015)


Endometriosis Association. 8585 North Seventy-Sixth Pl., Milwaukee, WI 53223-2600. Telephone: 414-355-2200. Website: http://www.endometriosisassn.org (accessed June 3, 2016).

National Institute of Child Health and Human Development. PO Box 3006, Rockville, MD 20847. Toll-free: 800-370-2943. Website: https://www.nichd.nih.gov/ (accessed December 11, 2015).

* fetus (FEE-tus) is an unborn human after it is an embryo, from nine weeks after fertilization until childbirth.

* menstrual cycle (MEN-stroo-al SYkul) culminates in menstruation (men-stroo-AY-shun), the discharging through the vagina of blood, secretions, and tissue debris from the uterus that recurs at approximately monthly intervals in females of reproductive age.

* hormones are chemical substances that are produced by various glands and sent into the bloodstream carrying messages that have certain effects on other parts of the body.

* ovaries (O-vuh-reez) are the sexual glands from which ova, or eggs, are released in women.

* intestines are the smooth muscle tubes through which food passes during digestion after it exits the stomach.

* immune system (im-YOON SIStem) is the system of the body composed of specialized cells and the substances they produce that help protect the body against disease-causing germs.

* rectum is the final portion of the large intestine that connects the colon to the outside opening of the anus.

* fallopian tubes (fa-LO-pee-an tubes) are the two slender tubes that connect the ovaries and the uterus in females. They carry the ova, or eggs, from the ovaries to the uterus.

* ultrasound is a diagnostic test during which sound waves are passed through the body to create images on a computer screen. Also called a sonogram.

* magnetic resonance imaging (or MRI) uses magnetic waves, instead of x-rays, to scan the body and produce detailed pictures of the body's structures.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)