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Updated: Jun 29, 2023

In endometriosis, tissue that's similar to the lining of the uterus is also growing in other places in the body. This can be very painful and could lead to infertility.

This article is pending medical review.


Written by Carolin Becker

Reviewed by Sophie Oppelt, Lea Dörner, Alessandra Papitto

Edited by Juliëtte Gossens


Endometriosis is a condition affecting around 10% of people with female reproductive organs. In this condition, tissue similar to the innermost lining of the uterus (womb), called the endometrium, grows outside the uterus in other places of the body. It can cause a range of symptoms, including pain, infertility, and heavy menstrual bleeding. Even though it's a common condition, endometriosis often goes misdiagnosed or undiagnosed. This can lead to physical and emotional suffering for those who are affected (1).

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What Is Endometriosis?

Basics of the menstrual cycle

To understand what endometriosis is, it’s helpful to know something about the menstrual cycle. In endometriosis, the lining of the womb is especially important. We explain in detail how the menstrual cycle works in this article. We’ll repeat the basics here as well.

As part of the monthly menstrual cycle, one egg is released from the ovaries during ovulation. From menstruation to ovulation, the inner lining of the uterus thickens in preparation for a fertilized egg. This inner lining is called the endometrium. It thickens so that a fertilized egg (blastocyst) can implant itself into the endometrium. From there, it can develop into an embryo and then a fetus. But if the egg that’s released during ovulation is not fertilized, the endometrium sheds and is released through the vagina. This leads to the monthly menstrual bleeding (your period).


But if you have endometriosis, endometrium also grows outside the uterus in other regions of the body. This could be the urinary tract, the bowels, the vagina or other places still (1). In these places, the endometrium also responds to your hormones. This means it also thickens and bleeds each month.

Endometrium in places other than the uterus has no way to leave the body. The tissue is trapped and can irritate the surrounding area. This can cause inflammation and pain. Sometimes, the inflammation causes the formation of scar tissue. This scar tissue can adhere to nearby organs, such as the bladder, intestines, or ovaries, causing them to stick together. These so-called adhesions can cause pain and other complications. Adhesions can distort the shape of the pelvic organs, leading to bowel or bladder dysfunction. They can also make it more difficult for the ovaries to produce and release eggs, and for the fallopian tubes to transport eggs to the uterus. This can lead to infertility (1).

Around 10% of people who can become pregnant are thought to be affected by endometriosis. But the condition is often unrecognized or misdiagnosed. That’s why the actual number might be much higher (2).

Symptoms and Signs

Symptoms of endometriosis vary from person to person. That is why it often takes a very long time for the condition to be discovered. In some people, it might not be discovered at all.

Common symptoms include:

  • Painful periods

  • Pain during sexual penetration

  • Painful urination

  • Painful bowel movements

  • Chronic worsening pain

  • Diarrhea

  • Constipation

  • Nausea

Ovarian cysts (endometriomas) can be found in more severe stages of endometriosis and can cause severe pain. These are small sacs of fluid (mostly blood) that grow in or on the ovaries.

In some cases, endometriosis can cause infertility, while others might not show any of the mentioned symptoms (1, 2).

Risk Factors and Causes

Some risk factors include having an early menarche (first period of your life), having a short menstrual cycle, hormonal imbalances, and drinking lots of alcohol (1).

Studies have suggested that you can be at a higher risk for endometriosis if someone that is genetically related to you also has the condition. If you are infertile or you have irregular period cycles, you might also be more likely to have endometriosis.

Irregular and heavy periods could be the result of high estrogen levels. Options to treat and manage these issues include estrogen-lowering medication, a healthy diet including foods such as citrus, and regular exercise (2, 3).

The cause for endometriosis is unclear to this day. But there are some theories on how the condition might develop (4).

Retrograde menstruation: “Retrograde” means backward. According to this theory, menstrual blood is not released from the body through the vagina, but flows back into the pelvic cavity via the fallopian tubes. Menstrual blood contains cells from the endometrium. These endometrial cells can then attach to organs in the pelvic cavity such as the bladder or the bowel, leading to endometriosis.

Coelomic metaplasia: The word “coelomic” relates to spaces in the body, in this cases the pelvic cavity. “Metaplasia” means a transformation of one cell type into another. This theory suggests that certain types of cells in the pelvic lining (outside the uterus) can transform into endometrial cells, leading to the development of endometriosis.

Immune system dysfunction: An abnormal immune response might contribute to the development of endometriosis. The immune system may be unable to recognize and destroy endometrial cells that have implanted outside the uterus. This would allow them to grow there, undisturbed, leading to endometriosis.

Genetic predisposition: Studies have suggested that certain genes may be linked to an increased risk of developing endometriosis (4).

It’s likely that endometriosis is caused by multiple factors. Research is being done to better understand it. While the exact cause of endometriosis is still unknown, early diagnosis and treatment can help manage symptoms and prevent long-term complications.


Diagnosis of endometriosis is crucial, because it’s a progressive disease that gets worse over time for most people. It can be difficult to diagnose endometriosis for several reasons:

  • Symptoms are not specific for endometriosis

  • Symptoms can vary from person to person

  • There is a lack of awareness about endometriosis, including among doctors and healthcare workers

  • Symptoms that go with the condition are often normalized (such as a very painful period or pain during sex)

There are also no specific, clinically proven blood tests, for example. Because the disease can occur in many parts of the body, a correct diagnosis is important for developing the right treatment strategy.

A pelvic exam, ultrasound, or MRI may help identify any abnormal growths or cysts. But because they’re so small, they are often not detectable with these methods.

The only definite way to diagnose endometriosis is via laparoscopy. During this procedure, your doctor inserts a small tube with a camera (a laparoscope) through a small incision in your belly. It’s usually only done when your doctor is planning on surgically removing the endometriosis or scar tissue. Even though it’s a small surgery, it’s still a surgery that comes with risks. That’s why scientists are working hard to find other tests that could make diagnosis easier and more pleasant for affected people (1).

One such option could be a saliva test. A study published in January 2022 found promising results for diagnosing endometriosis based on micro-RNA (little molecules that control many pathways in our body) found in the saliva of patients. The test will be available soon in several European countries. Its availability and price are still being evaluated by health authorities (3).


Before choosing a treatment, your doctor should carefully consider the symptoms you are experiencing. They should also consider the location of the disease. This way, they can try to prevent the symptoms from reoccurring.

Often, pain medication is given to provide relief from chronic pain. Hormone therapy like contraceptive pills could be used to prevent abnormal bleeding and build-up of endometrial tissue. In some cases, surgery might be an option to remove scar tissue or endometrial build-up (1, 2). It's important to know that even if you get surgery, symptoms could come back later on.


Many women worldwide are affected by endometriosis and its symptoms, including pain, heavy bleeding, and infertility. While the exact cause of endometriosis is not fully understood, treatment options are available to help manage symptoms and improve quality of life. Women and anyone else who experiences symptoms of endometriosis should speak with their healthcare provider for an accurate diagnosis and to discuss treatment options.



  1. Zondervan KT, Becker CM, Missmer SA. Endometriosis. New England Journal of Medicine. 2020;382(13):1244-1256. DOI: 10.1056/NEJMra1810764

  2. Parasar P, Ozcan P, Terry KL. Endometriosis: Epidemiology, Diagnosis and Clinical Management. Current Obstetrics and Gynecology Reports. 2017;6(1):34-41. DOI: 10.1007/s13669-017-0187-1

  3. Bendifallah S, Suisse S, Puchar A, Delbos L, Poilblanc M, Descamps P, et al. Salivary MicroRNA Signature for Diagnosis of Endometriosis. Journal of Clinical Medicine. 2022;11(3). DOI: 10.3390/jcm11030612

  4. Sourial S, Tempest N, Hapangama DK. Theories on the pathogenesis of endometriosis. International Journal of Reproductive Medicine. 2014;2014:179515. DOI: 10.1155/2014/179515

Please note: the information we provide to you here is for educational purposes only. If you’re experiencing any discomfort or have any complaints or questions about your health, please contact your doctor or other relevant health professional. We don’t provide medical advice.


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