What is endometriosis?

What is endometriosis disease?

Endometriosis is a condition where tissue similar to the uterine lining grows outside the uterus. The growths are benign, which means they are not cancerous, according to the US Office on Women's Health. If your main question is about period pain in general, our page on menstrual cramps is a good place to start, and heavy periods have a page of their own too.

What causes endometriosis is not known. The National Institute of Child Health and Human Development (NICHD), part of the US National Institutes of Health, describes two main theories: retrograde menstruation (menstrual blood flowing backward) and coelomic metaplasia (other cells changing into lining-like tissue). Neither explains every case, such as endometriosis found in the lungs. The NHS in the UK likewise says it is not known what causes it.

How is endometriosis diagnosed and treated?

Diagnosis usually starts with a pelvic exam and may continue with an ultrasound, an MRI or a trial of hormonal medicine. The US Office on Women's Health says surgery (laparoscopy) is the only way to be sure. The World Health Organization (WHO) says a clinical diagnosis can be made from symptoms and imaging such as ultrasound or MRI, so surgery is not always needed before treatment begins.

In the UK, the NHS describes a similar route: your GP examines you and may arrange an ultrasound, an MRI or a laparoscopy (keyhole surgery). Laparoscopy can confirm the diagnosis and allow some affected areas to be removed.

Tissue removed during surgery can be examined, which is where an endometriosis biopsy comes in. It is one tool among several, and it is worth asking your provider what they expect it to add in your situation.

There is no cure, but endometriosis treatments can ease symptoms. In the US, hormonal birth control is usually the first step if you are not trying to get pregnant. A GnRH agonist, a type of hormone medicine, may be prescribed if you are trying to conceive. Surgery is generally reserved for severe symptoms, for when hormones have not helped, or for fertility problems. You may read about ablation and excision when looking into surgery to treat endometriosis; it is worth asking your surgeon which approach is planned and why.

The NHS lists pain relievers such as paracetamol (acetaminophen in the US) and ibuprofen, plus hormonal treatments such as the combined pill. Surgical options in the UK include removing endometriosis or ovarian cysts and, in some cases, hysterectomy or oophorectomy (removal of the ovaries). Therapy for endometriosis can also go beyond medicine: WHO lists physiotherapy and cognitive behavioral therapy as options that can help with pain and quality of life, and the NHS lists pain and fatigue management and mental health support.

How common is endometriosis, and how long does diagnosis take?

Endometriosis and PCOS (polycystic ovary syndrome) each affect about 1 in 10 women, and endometriosis often takes 7 years or more to diagnose, according to NICE NG73 and the International PCOS Guideline (2023).

In the US, the Office on Women's Health says endometriosis may affect more than 11% of women aged 15 to 44, an estimated 6.5 million or more. Worldwide, WHO estimates that 10% of reproductive-age women, about 190 million, are affected.

WHO puts the average time to diagnosis at 4 to 12 years, a wide range that includes the 7 years or more above. That long wait is why it helps to keep a simple record of your pain days, your cycle, what you took and whether it helped, and to raise it again if you are not getting answers. These numbers describe large groups, not you, but they show that endometriosis is common and that asking again is reasonable.

What do the guidelines agree on, and where do they differ?

Taken together, the US Office on Women's Health, WHO, the NHS and NICHD give a consistent picture: endometriosis is common, its growths are benign, its cause is unknown, and there is no cure but there are treatments that ease symptoms. The two figures for time to diagnosis, 7 years or more and 4 to 12 years, both point to a long wait.

They differ on one point: whether surgery is needed to confirm it. The US Office on Women's Health names laparoscopy as the only way to be sure, while WHO says a clinical diagnosis can be made from symptoms and imaging. It is reasonable to ask your provider whether imaging is enough to start treatment in your case, or whether a laparoscopy would change the plan.

On safety, the evidence is reassuring. The Office on Women's Health does not call the condition life-threatening, though it notes complications such as blocked tubes, cysts, scar tissue and infertility, plus links to some cancers and autoimmune diseases. That is a reason to stay in touch with your provider, not a reason for alarm. This page does not rank one kind of surgery above another or say what a biopsy result means for any one woman; those are questions for the surgeon who knows your situation.

Next steps

If pelvic pain or period symptoms are disrupting your life, a good place to start is a visit to your provider (your GP in the UK) with a short record of when symptoms occur and how they affect you. Ask what tests make sense, what first treatments are available, and what to do if they do not help. See a doctor sooner if your symptoms are getting worse, or if you have any bleeding 12 months or more after your last period. Treatment is a conversation about your symptoms, your plans for pregnancy and your preferences, and you decide what fits you: it is not one size fits all.