Endometriosis is when cells similar to the ones in the lining of the womb, or uterus, are found elsewhere in the body.
Not being in the womb does not prevent these cells behaving as if they were – they build up before breaking down and bleeding.
However, unlike the blood created in the womb, which leaves a woman's body as a monthly period, this blood remains in the body, causing inflammation, pain, and the formation of cysts and scar tissue.
As endometriosis often affects the ovaries and fallopian tubes, it can also lead to problems conceiving a child. If it affects the bowels, meanwhile, it can cause problematic bowel movements.
Endometriosis is one of the most common gynaecological conditions in the UK, affecting up to 50% of women with infertility(1).
Common symptoms of endometriosis include:
Not everyone with endometriosis has symptoms, though. Some women live with the condition for years without realising it. Among those with symptoms, the intensity can also vary widely.
Endometriosis affects as many as one in 10 women of reproductive age, many of whom have no symptoms. In the UK, this equates to around two million women(2).
There are three types of endometriosis, which can occur concurrently in some patients:
Nobody is totally sure what causes endometriosis, but there are a number of theories. These include:
Endometriosis is an infection. Fiction: endometriosis is neither an infection nor a form of cancer.
It can be difficult to diagnose endometriosis because the symptoms vary widely from one person to another and can often be caused by a variety of other conditions.
If you think you might have endometriosis, the first step is to visit your GP, who may want to examine your tummy and/or vagina. To improve your chances of getting the right diagnosis, it is often worth noting down your symptoms - or even keeping a diary of them - prior to your appointment.
If they think further examinations are required, you will then be referred to a gynaecologist, who will probably suggest an ultrasound scan or a laparoscopy - a type of keyhole surgery used to identify and sometimes resolve problems in your abdominal area, which is the only sure way to find out if you have endometriosis or not.
It takes the average woman with endometriosis more than seven years to get a diagnosis(3).
There's currently no cure for endometriosis, but there are treatments that can help to ease the symptoms.
These include:
One of the main complications linked to endometriosis is that it can make it harder for women to get pregnant.
Surgery to remove endometriotic tissue can help improve your chances of getting pregnant, as well as reducing the severity of any symptoms you are experiencing. However, there's no guarantee that you'll be able to get pregnant after surgery.
Surgery for endometriosis can also sometimes cause further problems, such as infections, bleeding or damage to the affected organs, so make sure you are aware of the risks before deciding whether or not to go ahead.
Jessica Bown is a freelance writer and journalist.