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Symptoms & causes

Endometriosis occurs when cells similar to those that line the uterus are found in other parts of the body, commonly a woman's pelvic and reproductive organs.[1] What happens when you have endometriosis, and its causes and symptoms, are discussed.

Topics on this page

What is endometriosis?

Endometriosis, pronounced end-o-me-tree-oh-sis (or just endo), is a progressive, chronic condition where cells similar to those that line the uterus (the endometrium) are found in other parts of the body. It most commonly occurs in the pelvis and can affect a woman's reproductive organs.

endometriosis uterus diagram

Studies suggest that endometriosis affects 1 in 10 women of reproductive age, with an estimated 176 million women worldwide having the condition.

The endometrial cells:

  • are found on organs in the pelvis
  • may start to grow and form patches or nodules on pelvic organs or on the peritoneum (the inside lining of the abdomen and pelvis; see image)
  • have the same cyclical/menstrual changes outside the uterus as inside the uterus
  • may bleed at the same time as your period (menstruation).

Endometrial cells found outside the uterus grow to form lesions or patches that bleed and leak fluid in response to your hormones at the time of the period. This leads to inflammation and scarring. These patches found outside the uterus cannot pass out of your body and remain in your pelvic cavity, on organs and other surfaces. On your ovaries, cysts called endometriomas can develop over time. These are sometimes called 'chocolate cysts' because of the darkish material they contain. On other surfaces the patches can form nodules.

What causes endometriosis?

We don't really know what causes endometriosis, and possible associations or factors can be different from woman to woman. Factors that have a role in causing endometriosis include:

  • Family history: Women who have a close relative with the condition are up to 7–10 times more likely to get endometriosis. Also, it is common with twins that both may get endometriosis, particularly if they are identical twins.[2, 3]
  • Retrograde (backwards) menstruation: When a woman has a period, the blood flows out of the vagina but also backwards along the fallopian tubes into the pelvis (called retrograde menstruation). In 90% of women, the blood, which contains endometrial cells, is absorbed or broken down by the body and causes no symptoms. However, in women with endometriosis, this endometrial tissue starts to grow, which can cause a wide range of symptoms.
  • Metaplasia: The conversion of the normal pelvic tissue into endometriosis.

Other possible factors that may have a role in causing endometriosis are:

  • having first pregnancy at an older age
  • heavy bleeding during periods, and periods lasting longer than five days
  • first period before 11 years of age
  • regularly having fewer than 27 days between periods, or having shorter regular cycles
  • changes in the immune cells
  • low body weight
  • alcohol use

In this video, Jean Hailes gynaecologist Dr Elizabeth Farrell gives a brief overview of the symptoms, management and treatment options for endometriosis.

Can I prevent endometriosis?

Endometriosis can't be prevented but is less likely to develop or progress if a woman reduces the number of menstrual cycles she experiences during her reproductive years. Factors that contribute to fewer menstrual cycles include:

  • hormonal therapy such as the combined oral contraceptive pill or progestins (may be given as tablets, an implant, an injection or an intrauterine device (IUD))
  • how many children you have – the chance of getting endometriosis may decrease with each pregnancy (this may be related to the hormone progesterone during pregnancy)
  • younger age of first pregnancy
  • breastfeeding for a longer period
  • regular exercise of more than four hours per week (this may also help with pelvic pain for endometriosis).

There may be different forms of endometriosis

  • Superficial endometriosis: here, superficial areas of disease appear on the lining of the pelvis and abdomen (called the peritoneum). These do not invade deeply into the tissues
  • Deep-infiltrating endometriosis: endometriosis lesions do invade deeply (more than 5mm) into the tissues and can lead to scarring and nodules. These can grow into nearby organs, such as the bladder, bowel and ovary
  • Ovarian disease: this may occur and is often considered a separate form of the disease. Here, burrowing lesions on and under the ovaries can lead to the development of 'chocolate cysts' or endometriomas
  • Adenomyosis is a different condition but can occur with endometriosis. In adenomyosis the cells similiar to the uterine lining can be present in the muscle wall of the uterus rather than outside the uterus.
  • Outside the pelvis: this is rare
  • Upper abdomen, eg on the diaphragm
  • In the liver, nose, eye
  • Abdominal wall, often associated with previous operation scarring.

How do you know if you have endometriosis?

The symptoms of endometriosis vary from woman to woman. Some women have many symptoms and severe pain, whereas others have no symptoms. The severity of the symptoms may not reflect the severity of the condition. The types of symptoms and their severity are likely to be related to the location of the endometrial tissue rather than the amount of endometrial cells growing.

Due to the varied symptoms, endometriosis can take a long time to diagnose (the average time to diagnosis is seven years). About a third of women with endometriosis discover they have it because they have not been able to become pregnant, or because endometriosis is found during an operation for another reason.

About three out of four women with endometriosis have pelvic pain and/or painful periods.

Symptoms can be extremely variable and may present with mild pain with periods or may be severe right from the outset of menstruation (menarche). For some women, there can be a slow and steady progression of symptoms (common); for others, symptoms may progress rapidly and affect multiple areas of the body and include non-gynaecological symptoms (less common).

Hithaishi had to convince doctors she wasn't drug seeking or had psychological issues before being diagnosed with endo. Watch the video and find out how she did it.

Symptoms you may experience

Pain is a key symptom of this condition. The pain is not related to how severe the disease is, but rather to the location of endometrial tissue.

The table below outlines the symptoms you might experience with endometriosis. Each woman with endometriosis will experience a different range of symptoms.


Pain immediately before and during a period (also called dysmenorrhoea).

Pain during or after sex (also called dyspareunia).

Abdominal, lower back and/or pelvic pain.

Pain on going to the toilet, passing urine, opening bowels.

Ovulation pain, including pain in the thigh or leg (this can also happen in women without endometriosis).

Pain that gets worse over time.

Severe pain that means you can't participate in work, school or sporting activities.


Heavy menstrual bleeding, with or without clots.

Irregular menstrual bleeding, with or without a regular cycle.

Bleeding longer than normal.

Bleeding before a period is due.

Bladder and bowel problems

Bleeding from the bladder or bowel.

Change in pattern of bowel habit, such as constipation, diarrhoea.

The need to urinate more frequently, or some other change from the normal habit.


Increased abdominal bloating, with or without pain at the time of the period.


Tiredness or lack of energy, especially around the time of the period.

Mood changes

Anxiety and depression due to ongoing pain.

Reduced quality of life

Taking days off work, study or school because of an inability to function normally.

Vaginal discomfort

Pelvic floor muscle spasm or tightening occuring because of fear of pain previously experienced with intercourse or tampon use.

Symptoms during menopause

Usually, endometriosis does go away after menopause. Uncommonly, it can return with the use of menopausal hormone therapy, or MHT (formerly called hormone replacement therapy, or HRT), especially if there is no progestogen component. Even more rarely, it can return for no reason without any hormonal treatment.

When to get help

Get help when period pain is stopping normal daily activities. For example when:

  • you are missing work, school or recreational activities
  • medicines used for period pain don't help reduce the pain
  • you need to stay in bed due to pain
  • symptoms are getting worse
  • you feel upset by your symptoms
  • your ability to cope mentally decreases.

This web page is designed to be informative and educational. It is not intended to provide specific medical advice or replace advice from your health practitioner. The information above is based on current medical knowledge, evidence and practice as at May 2019.


  • 1
    Giudice LC. Clinical practice: Endometriosis. N Engl J Med. 2010 Jun 24;362(25):2389–98.
  • 2
    Ahn SH, Monsanto SP, Miller C, Singh SS, Thomas R, Tayade C. Pathophysiology and immune dysfunction in endometriosis. Biomed Res Int. 2015;795976:1–12.
  • 3
    Carvalho L, Podgaec S, Bellodi-Privato M, Falcone T, Abrão MS. Role of eutopic endometrium in pelvic endometriosis. J Minim Invasive Gynecol. 2011 Jul–Aug;18(4):419–27.
  • 4
    Riazi H,Tehranian N, Ziaei S, Mohammadi E, Hajizadeh E, Montazeri A. Clinical diagnosis of pelvic endometriosis: a scoping review. BMC Women's Health. 2015;15:(39) 1–12.
Last updated: 04 June 2021 | Last reviewed: 15 May 2019

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