Overview
Endometriosis is a condition where tissue similar to the lining of the uterus grows outside the uterus, commonly on the ovaries, fallopian tubes, and pelvic tissues. Each month this tissue responds to hormonal changes, causing inflammation, pain, and scarring. It is a significant cause of period pain, chronic pelvic pain, and infertility.
How common is it?
Endometriosis affects around 1 in 10 women of reproductive age worldwide, equivalent to approximately 1.5 million women in the UK.
Causes and risk factors
The exact cause is not fully understood. The most accepted theory involves retrograde menstruation, where menstrual blood flows backwards through the fallopian tubes into the pelvis. Genetic and immune factors also play a role.
Common risk factors
- Family history of endometriosis
- Starting periods early or having long or heavy periods
- Having a shorter than normal menstrual cycle
- Never having been pregnant
- Immune system abnormalities preventing clearance of misplaced tissue
Symptoms
- Very painful periods (dysmenorrhoea)
- Chronic pelvic pain between periods
- Pain during or after sexual intercourse
- Painful bowel movements or urination, particularly during periods
- Heavy menstrual bleeding
- Difficulty becoming pregnant
- Fatigue
- Some women have no symptoms at all
When to see a doctor
See a doctor if period pain is severe enough to interfere with daily life, pain during sex is a problem, or you are having difficulty conceiving.
Diagnosis
Assessment starts with symptoms, medical history and examination. Ultrasound and sometimes MRI help investigate suspected endometriosis, but normal imaging does not exclude it. Laparoscopy may be offered to confirm the diagnosis or treat disease. Symptom treatment can begin while investigations and referral proceed; surgery is not required before every patient can receive treatment.
Treatments
Hormonal therapy
Combined oral contraceptive pill, progestogens, and the Mirena IUS suppress ovulation and endometrial growth, reducing pain. These manage symptoms but do not cure the condition.
Surgery
Surgery to remove endometriosis may help some people, particularly when other treatments are unsuitable or ineffective. Benefits, recurrence, complications and fertility goals should be discussed with a specialist. Surgery is not automatically a better option than hormonal treatment for everyone.
Analgesics and NSAIDs
Ibuprofen and naproxen taken regularly around the menstrual period reduce pain by inhibiting prostaglandin production.
Self-care and lifestyle
- Heating pads provide symptomatic relief during painful periods
- Adapt activity to your symptoms and discuss pain-management support with your care team.
- Avoid assuming that a particular diet will treat endometriosis. Seek individual advice if symptoms or food restrictions are affecting nutrition.
- Psychological support and pain management therapy help with chronic pain
Prevention
There is no known way to prevent endometriosis. Earlier diagnosis and treatment reduce the impact on fertility and quality of life.
Sources for targeted updates
Updated: 11 September 2026. Diagnosis, treatment choice and unsupported lifestyle claims. This update covers the named sections; a full review of the remaining guide is pending.