Endometriosis is a common condition where tissue that behaves like the lining of the womb (the endometrium) is found outside the womb.

These pieces of tissue can be found in many different areas of the body, but they are most commonly found on the ovaries, on the lining of the pelvis behind the uterus and covering the top of the vagina.

The condition is estimated to affect around two million women in the UK. Most of them are diagnosed between the ages of 25 and 40.

Endometriosis is a long-term (chronic) condition that causes painful periods or heavy periods. It often also causes pain in the lower abdomen (tummy), pelvis or lower back, as well as fertility problems. It may also contribute towards a lack of energy and depression.

However, the symptoms of endometriosis can vary significantly and some women have few symptoms or no symptoms at all.

You should see your GP if you have symptoms of endometriosis so they can try to identify a cause and refer you to a specialist for a diagnosis if necessary.

Read more about the symptoms of endometriosis and diagnosing endometriosis.

What causes endometriosis?

The causes of endometriosis are not fully known, but there are several theories. The most widely accepted theory is that the womb lining does not leave the body properly during a period and embeds itself on the organs of the pelvis, although this doesn’t explain why the condition can occur in women who have had a hysterectomy.

The endometriosis cells behave in the same way as those that line the womb, so every month they grow during the menstrual cycle and bleed. Normally, before a period the hormone oestrogen causes the endometrium to thicken to receive a fertilised egg. If the egg isn’t fertilised, the lining breaks down and leaves the body as a period.

Endometriosis tissue elsewhere in the body will go through the same process of thickening and shedding, but it has no way of leaving the body. This leads to pain, swelling and sometimes fertility problems if the fallopian tubes or ovaries are damaged.

Endometriosis is rare in women who have been through the menopause as this causes oestrogen to be permanently reduced.

Read more about the causes of endometriosis.

How endometriosis is treated

There is no known cure for endometriosis. However, the symptoms can often be managed with painkillers or hormone medication, which help prevent the condition from interfering with your daily life.

Surgery to remove patches of endometriosis tissue can sometimes be used to improve symptoms and fertility.

Endometriosis can be a difficult condition to deal with, both physically and emotionally. Charities such as Endometriosis UK and Endometriosis SHE Trust UK can offer advice and support to help you cope.

Read more about treating endometriosis.

Endometriosis and pregnancy

One of the main complications of endometriosis is difficulty getting pregnant or not being able to get pregnant (infertility).

Although surgery cannot guarantee that you will be able to get pregnant, there is good evidence that removing visible areas of endometriosis with a laser or an electric current during keyhole (laparoscopic) surgery can improve your chances of having a successful pregnancy.

If you have endometriosis and you do become pregnant, the condition is unlikely to put your pregnancy at risk.

Pregnancy sometimes reduces the symptoms of endometriosis, although they often return once you have given birth and finished breastfeeding and the menstrual cycle returns to normal.

Read more about the complications of endometriosis and how infertility is treated.

Symptoms of endometriosis

Symptoms of endometriosis can vary significantly from person to person. Some women have no symptoms at all.

The most common symptoms include:

  • painful periods or heavy periods
  • pain in the lower abdomen (tummy), pelvis or lower back
  • pain during and after sex
  • bleeding between periods
  • difficulty getting pregnant

The experience of pain varies between women. Most women with endometriosis get pain in the area between their hips and the tops of their legs. Some women have this all the time, while others only have pain during their periods, when they have sex or when they go to the toilet.

Other symptoms may include:

  • long-term exhaustion and tiredness
  • discomfort when urinating or passing stools
  • bleeding from your back passage (rectum) or blood in your stools
  • coughing blood (in rare cases where the endometriosis tissue is in the lung)

How severe the symptoms are depends largely on where in your body the endometriosis is, rather than the amount of endometriosis you have. A small amount of tissue can be as painful as, or more painful than, a large amount.

You should see your GP if you have symptoms of endometriosis so they can try to identify a cause and refer you to a specialist if necessary.

Causes of endometriosis

The exact cause of endometriosis is unknown, but there are several theories about what causes it. 

Retrograde menstruation

Retrograde menstruation is when the womb lining (endometrium) flows backwards through the fallopian tubes and into the abdomen (tummy) instead of leaving the body as a period. This tissue then embeds itself on the organs of the pelvis and grows.

It is thought that retrograde menstruation happens in most women, but many are able to clear the tissue naturally without it becoming a problem. It is possible that this is how endometriosis occurs in some women.

Retrograde menstruation is the most commonly accepted theory for endometriosis. However, it does not explain why the condition can occur in women who have had a hysterectomy.


Endometriosis is sometimes believed to be hereditary, being passed down through the genes of family members. It can affect women of every ethnicity, but is less common in women of African-Caribbean origin and more common in Asian women than in white women. This suggests that genes may play a part.

Spread through the bloodstream or lymphatic system

Although it is not known how, endometriosis cells are believed to get into the bloodstream or lymphatic system (a network of tubes, glands and organs that is part of the body’s defence against infection). This theory could explain how, in very rare cases, the cells are found in remote places such as the eyes or brain.

Problems with the immune system

It is believed that some women’s immune systems are not able to fight off endometriosis effectively. Many women with endometriosis are found to have lower immunity to other conditions. However, this may be a result of the endometriosis rather than the cause of the condition.

Environmental causes

It is thought that endometriosis may be caused by certain toxins in the environment, such as dioxins, that affect the body, the immune system and the reproductive system.

However, while research suggests there is a link between endometriosis and high levels of dioxin exposure in animals, it is not currently known if this is also the case in humans.


Metaplasia is the process of one type of cell changing into another to adapt to its environment. It is this development that allows the human body to grow in the womb before birth.

It has been suggested that some adult cells may retain this ability to change, and that the shedding of menstrual blood or blood products into the pelvis during menstruation may stimulate them to transform into endometrial cells.

Diagnosing endometriosis

Treating endometriosis

There is no cure for endometriosis and it can be difficult to treat. Treatment aims to ease symptoms so the condition doesn’t interfere with your daily life.

Treatment will be given to:

  • relieve pain
  • slow the growth of endometriosis tissue
  • improve fertility
  • prevent the disease returning

Deciding which treatment

Your gynaecologist will discuss the treatment options with you and outline the risks and benefits of each.

When deciding which treatment is right for you, there are several things to consider, including:

  • your age
  • whether your main symptom is pain or difficulty getting pregnant
  • whether you want to become pregnant (some treatments may stop you getting pregnant)
  • how you feel about surgery
  • whether you’ve tried any of the treatments before

Treatment may not be necessary if your symptoms are mild and you have no fertility problems or if you’re nearing the menopause, when symptoms may get better without treatment.

Endometriosis gets better by itself without treatment in about 3 in every 10 cases, but it becomes worse without treatment in about 4 in every 10 cases.

One course of action is to keep an eye on symptoms and decide to have treatment if they get worse.

Support from self-help groups, such as Endometriosis SHE Trust UK and Endometriosis UK, can be very useful if you’re learning how to manage endometriosis.

Pain medication

Non-steroidal anti-inflammatories (NSAIDs), such as ibuprofen and naproxen, are usually the preferred painkiller used to treat the pain associated with endometriosis. This is because they act against the inflammation (swelling) caused by the condition, which may help ease pain and discomfort. It’s best to take NSAIDs the day before (or several days before) you expect the period pain.

Paracetamol can be used to treat mild pain. It’s not usually as effective as NSAIDs, but may be used if these types of drugs cause any side effects, such as nausea, vomiting and diarrhoea.

Codeine is a stronger painkiller that’s sometimes combined with paracetamol or used alone if other painkillers aren’t suitable. However, constipation is a common side effect that may aggravate the symptoms of endometriosis.

For more information, read the Endometriosis UK factsheet on pain management for endometriosis.

Hormone treatments

The aim of hormone treatments is to limit or stop the production of oestrogen in your body. This is because oestrogen encourages endometriosis tissue to grow and shed. Without exposure to oestrogen, the endometriosis tissue can be reduced, which helps ease the symptoms.

However, hormone treatment has no effect on adhesions (“sticky” areas of tissue that can cause organs to fuse together) and can’t improve fertility.

Read more about adhesions and other complications of endometriosis.

Some of the main hormone-based treatments for endometriosis include:

Evidence suggests these hormone treatments are equally effective in treating endometriosis, but they have different side effects. Although most hormone treatments reduce your chance of pregnancy while using them, only the contraceptive pill or patch and LNG-IUS are licensed to be used as contraceptives.

Progestogens and antiprogestogens are used less commonly these days because they often cause unpleasant side effects.

The combined oral contraceptive pill or patch

The combined contraceptive pill and contraceptive patch contain the hormones oestrogen and progestogen. They can help relieve milder symptoms and can be used over long periods of time. They stop eggs being released (ovulation) and make periods lighter and less painful.

These contraceptives can have side effects, but you can try different brands until you find one that suits you. Your doctor may recommend taking three packs of the pill in a row without a break to minimise the bleeding and improve any symptoms related to the bleeding.

Levonorgestrel-releasing intrauterine system (LNG-IUS)

The Mirena levonorgestrel-releasing intrauterine system (LNG-IUS) is a T-shaped contraceptive device that fits into the womb. It releases a type of progestogen hormone called levonorgestrel.

This hormone prevents the lining of your womb growing quickly, which can help reduce pain and greatly reduces or even stops periods.

The device is put into the womb by a doctor or nurse. Once in place, it can remain effective for up to five years.

Possible side effects of using LNG-IUS include irregular bleeding that may last more than six months, breast tenderness and acne.

Learn more about the IUS.

Gonadotrophin-releasing hormone (GnRH) analogues

GnRH analogues are synthetic hormones that bring on a temporary artificial menopause by reducing the production of oestrogen. They’re usually taken as a nasal spray or injection.

Menopause-like side effects of GnRH analogues include hot flushes, vaginal dryness and low libido. Sometimes low doses of hormone replacement therapy (HRT) may be recommended in addition to GnRH analogues to prevent these side effects.

They’re only prescribed on a short-term basis (normally a maximum of six months at a time) and your symptoms may return after treatment is stopped.

GnRH analogues aren’t licensed as a form of contraception, so you should still use contraception in the first month while taking them until they take full effect.

Examples of GnRH analogues include:

  • buserelin
  • goserelin
  • nafarelin
  • leuprorelin


Progestogens, such as norethisterone, are synthetic hormones that behave like the natural hormone progesterone. They work by preventing the lining of your womb and any endometriosis tissue growing quickly.

However, they have side effects such as:

  • bloating
  • mood changes
  • irregular bleeding
  • weight gain

Progestogens are usually taken daily in tablet form from days 5 to 26 of your menstrual cycle, counting the first day of your period as day one.

Progestogen tablets aren’t an effective form of contraception, so you’ll still need to use contraception while taking them if you don’t want to get pregnant.


Also known as testosterone derivatives, antiprogestogens are synthetic hormones that work in a similar way to GnRH analogues. They bring on a temporary artificial menopause by decreasing the production of oestrogen.

Side effects of antiprogestogens can include:

  • weight gain
  • acne
  • mood changes
  • the development of masculine features such as hair growth and a deepening voice

These side effects are often severe and alternative medications are more effective. This means antiprogestogens are usually only prescribed as a last resort, if other medications haven’t worked.

Like GnRH analogues, antiprogestogens are usually only prescribed for a maximum of six months at a time.

Examples of antiprogestogens include danazol and gestrinone.


Surgery can be used to remove or destroy areas of endometriosis tissue, which can help improve symptoms and fertility. The kind of surgery you have will depend on where the tissue is. The options are:

  • laparoscopy (the most commonly used and least invasive technique)
  • laparotomy
  • hysterectomy

Any surgical procedure carries risks. It’s important to discuss these with your surgeon before undergoing treatment.


Laparoscopy, also known as keyhole surgery, is a common procedure used to treat endometriosis. Small cuts (incisions) are made in your tummy so the endometriosis tissue can be destroyed or cut out.

Large incisions can be avoided because the surgeon uses an instrument called a laparoscope. This is a small tube with a light source and a camera, which relays images of the inside of your tummy or pelvis to a television monitor.

During laparoscopy, fine instruments are used to apply heat, a laser, an electric current (diathermy) or a beam of special helium gas to the patches of tissue to destroy or remove them.

The procedure is carried out under general anaesthetic, so you’ll be asleep during the procedure and won’t feel any pain as it’s carried out.

Ovarian cysts, or endometriomas, which are formed as a result of endometriosis, can also be removed using this technique.

Although this kind of surgery can relieve your symptoms and has been shown to improve fertility, problems can sometimes recur, especially if some endometriosis tissue is left behind.


A laparotomy is a more invasive operation used if your endometriosis is severe and extensive or if some of your organs have fused together.

During the procedure, the surgeon makes a wide cut along the bikini line and opens up the area to access the affected organs and remove the endometriosis tissue.

Recovery time for this type of surgery is longer than for keyhole surgery.


If keyhole surgery and other treatments haven’t worked and you’ve decided not to have any more children, a hysterectomy (removal of the womb) can be an option. However, this is rarely required.

A hysterectomy is a major operation that will have a significant impact on your body. Deciding to have a hysterectomy is a big decision that you should discuss with your GP or gynaecologist.

Hysterectomies can’t be reversed and, though unlikely, there’s no guarantee the endometriosis symptoms won’t return after the operation. If the ovaries are left in place, the endometriosis is more likely to return.

If your ovaries are removed during a hysterectomy, the possibility of needing HRT afterwards should be discussed with you. However, it’s not clear what course of HRT is best for women who have endometriosis.

For example, oestrogen-only HRT may cause your symptoms to return if any endometriosis patches remain after the operation. This risk is reduced by the use of a combined course of HRT (oestrogen and progesterone), but this can increase your risk of developing breast cancer.

However, the risk of breast cancer isn’t significantly increased until you’ve reached the normal age of the menopause. Talk to your doctor about the best treatment for you.

Complications of endometriosis