What endometriosis is
Endometriosis is a disease in which tissue similar to the lining of the womb grows outside the womb. This tissue can cause inflammation, pain and scarring in the pelvis and, less often, in other parts of the body. The World Health Organization estimates that it affects about 10% of women and girls of reproductive age worldwide, or around 190 million people (WHO fact sheet, 15 October 2025).
It is a chronic condition. Its severity varies widely: some people have few or no symptoms, while for others it affects work, relationships and mental health.
The symptoms
The WHO lists the main symptoms as:
- severe pain during periods;
- heavy menstrual bleeding;
- chronic pelvic pain;
- pain during or after sex, or when opening the bowels or passing urine;
- abdominal bloating and nausea;
- difficulty getting pregnant.
The WHO also notes effects on mental health, such as anxiety and depression, which are linked to living with chronic pain. Painful periods are common and are not always a sign of endometriosis; pain that stops normal activities is a reason to seek advice.
Why diagnosis takes so long
According to the WHO, the average time from the first symptoms to a diagnosis is 4 to 12 years. Several factors contribute. Period pain is often treated as normal, symptoms overlap with other conditions, and the traditional way of confirming the diagnosis is surgery.
The WHO describes two routes. Diagnosis can be made by laparoscopic surgery, in which a camera is used to look inside the abdomen, or clinically, from symptoms and imaging such as ultrasound or MRI. New, less invasive tests are under development, including symptom checklists, blood tests and tests using saliva or menstrual blood, but they are not yet part of standard practice everywhere.
Endometriosis and fertility
Endometriosis is one of the recognised causes of infertility, listed by both the WHO and the NHS among the main identifiable causes (see how common is infertility?). Inflammation and scarring can affect the ovaries, the fallopian tubes and the pelvis. Many people with endometriosis still conceive without treatment; others need fertility treatment, including IVF.
Treatment options
There is currently no cure. Treatment aims to control symptoms and, where relevant, to improve the chance of pregnancy. The WHO lists:
- pain relief, including non-steroidal anti-inflammatory drugs (NSAIDs) and other painkillers;
- hormonal medicines, which can reduce or stop periods and slow the growth of the tissue;
- aromatase inhibitors in some cases;
- surgery to remove endometriosis tissue;
- fertility treatments for those trying to conceive.
The WHO also mentions physiotherapy and cognitive behavioural therapy as ways of managing pain and improving quality of life. The right combination depends on symptoms, age, and whether pregnancy is wanted, which is why treatment plans differ so much between patients.
What the research is looking at
Endometriosis has long been under-researched relative to how common it is. Current work focuses on non-invasive diagnosis, the biology of how the tissue grows outside the womb, and better long-term treatments. When reading news about a "breakthrough", it is worth checking what kind of study it is: early laboratory and animal findings often do not translate into treatments. Our guide to reading a reproduction study explains what to look for.
Related conditions
Endometriosis is sometimes confused with polycystic ovary syndrome, which is a different condition with different symptoms and causes. See PCOS explained for how the two differ.
This article summarises official guidance and is not medical advice. If you have symptoms such as severe period pain or pain that affects daily life, talk to a GP or gynaecologist.
Preparing for an appointment
Because diagnosis often takes years, people with suspected endometriosis are frequently advised to arrive at appointments with clear information. A simple diary of symptoms over two or three cycles helps: when pain occurs, how severe it is, whether it stops normal activities, how heavy bleeding is, and which painkillers have been tried. It is reasonable to ask whether referral to a gynaecologist, or to a specialist endometriosis centre, would be appropriate, especially if symptoms persist despite treatment.
Endometriosis and daily life
The WHO describes endometriosis as a condition with significant social, public health and economic implications, because chronic pain and fatigue can affect education, work and relationships. Adjustments at school or work, such as flexible hours during bad days, can make a real difference, and many patient organisations provide guidance for employers as well as patients.
Trying to conceive with endometriosis
For people with endometriosis who want to become pregnant, the general guidance on preparing for pregnancy still applies, from folic acid to stopping smoking (see before trying for a baby). Some hormonal treatments for endometriosis act as contraceptives, so treatment plans usually change when pregnancy is wanted. A specialist can explain when surgery or fertility treatment may help.
Common misunderstandings
- "Period pain is always normal." Some discomfort is common, but pain that stops normal activities, or does not respond to usual painkillers, deserves medical attention.
- "Pregnancy cures endometriosis." Symptoms may ease during pregnancy for some people, but pregnancy is not a treatment and symptoms often return.
- "Surgery always solves it." Surgery can relieve symptoms for many patients, but endometriosis can come back, and the WHO is clear that there is currently no cure.
- "It only affects fertility." For many people the main problem is pain and its effect on daily life, whether or not they want children.