What is Endometriosis?

Endometriosis is a chronic and painful disease


About 1 in 10 women of reproductive age has endometriosis. It occurs when tissue that normally lines the inside of the uterus starts growing outside of the uterus, where it doesn’t belong.

This out-of-place tissue, often called a lesion or an implant, can cause severe pain and inflammation throughout the month.



Click to watch the “Inner Workings of Endometriosis” video

Discover the inner workings of endometriosis

What’s actually happening inside the body of a woman with endometriosis? And why does it hurt? Watch this video to find out.


Symptoms are different for every woman, and not all women have all 3

Learn more about the variety of symptoms that women with endometriosis can experience.

Common symptoms of endometriosis include:

  • Painful periods
  • Pelvic pain in between periods
  • Pain with sex

But women with endometriosis can experience a variety of different symptoms. Their symptoms may reflect the area where endometriosis is located. Learn more here.


The exact cause is unknown

One popular theory as to what causes endometriosis is something called retrograde menstruation, which is when, during menstruation, the lining of the uterus flows in the opposite direction of the way it’s supposed to. But it’s not certain this is the cause.

Learn more about retrograde menstruation and explore other possible causes of endometriosis here.

Symptoms may depend on where the endometrial lesions are located

The location of endometrial lesions can affect what kind of symptoms a woman experiences. For example, if she has lesions on her bladder, she may have pain while urinating. Learn more about the different places lesions may develop and the symptoms they can cause here.



Click to watch a video of women discussing how endometriosis has affected them

Hear from real women with endometriosis

“I missed school. I missed events…I missed one of my best friend’s weddings.” Watch this video to hear women discuss how endometriosis has impacted them.

View transcript

Stages of endometriosis: 1, 2, 3, 4

Endometriosis is described as having 4 stages. Doctors classify these stages as:

  • Stage 1 – minimal
  • Stage 2 – mild
  • Stage 3 – moderate
  • Stage 4 – severe

But it’s important to know that these stages have nothing to do with how painful the disease is. For example, a woman with stage 1 endometriosis might have severe pain, while a woman with stage 4 has no pain at all.

Instead, the stages have to do with the size of the endometrial lesions, their location in the body, the amount of them, and their depth (whether it’s on the surface of an organ or deep within it).


Discover treatment options for endo pain

It's important to talk to your doctor about all your treatment choices.
Learn more about a specific option that could be right for you.



References: 1. American College of Obstetricians and Gynecologists. Practice bulletin no. 114: management of endometriosis. Obstet Gynecol. 2010;116(1):223-236. 2. American College of Obstetricians and Gynecologists. Frequently asked questions. FAQ013. Gynecologic problems. https://www.acog.org/~/media/For%20Patients/faq013.pdf?dmc=1. Updated October 2012. Accessed January 8, 2020. 3. Fischer JR. APGO Educational Series on Women’s Health Issues. Diagnosis & management of endometriosis: pathophysiology to practice. Association of Professors of Gynecology and Obstetrics; 2012. 4. Liu JH. Merck Manuals. Consumer Version. Women’s Health Issues. Endometriosis. https://www.merckmanuals.com/home/women-s-health-issues/endometriosis/endometriosis. Updated February 2019. Accessed January 8, 2020. 5. American Society for Reproductive Medicine. ASRM Patient Information Series. Endometriosis—a guide for patients; revised 2012. 6. Giudice LC. Clinical practice: endometriosis. N Engl J Med. 2010;362(25):2389-2398.