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NHS Choices Condition

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The exact cause of endometriosis is unknown, but there are a number of theories:

  • retrograde menstruation
  • genetic predisposition
  • spreading through the bloodstream or lymphatic system
  • immune dysfunction
  • environmental causes
  • metaplasia

It is likely that endometriosis is caused by a combination of genetic, immune system and hormonal factors.

Retrograde menstruation

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

It is thought that retrograde menstruation happens in most women, but that they 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.

Genetic disposition

Endometriosis is sometimes believed to be hereditary, being passed down through the genes of family members. It is rare in women of African-Caribbean origin, and is more common in Asian women than in white (Caucasian) women. This suggests that genes may be involved.

Spreading 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.

Immune dysfunction

It is believed that some women's immune systems are not able to effectively fight off endometriosis. Many women with endometriosis are said to have lower immunity to other conditions. However, this may be a result of the endometriosis, rather than something that is caused by the disease.

Environmental causes

It is thought that endometriosis may be caused by certain toxins in the environment, such as dioxins (chemical byproducts) affecting the body and its immune system.


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 retain the ability they had as an embryo to transform into endometrial cells.

view information about Endometriosis on www.nhs.co.uk »

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