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. Doctors refer to this as retrograde menstruation.
Doctors have reported seeing this lining coming backwards along the fallopian tubes and into the tummy, and it has also been shown to be capable of growing into the lining of the pelvis on the inside of the tummy.
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.