Causes of endometriosis

The exact cause of endometriosis is unknown, but there are several theories.

Retrograde menstruation

Retrograde menstruationis 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's thought retrograde menstruation happens in most women, butmany are able to clear the tissue naturally without it becoming a problem.

Retrograde menstruation is the most commonly accepted theory for endometriosis. However, it doesn't 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's more common in the sisters and mothers of women who have endometriosis.

It can affect women of every ethnicity, but is:

  • less common in women of African-Caribbean origin
  • more common in Asian women than in white women

This suggests genes may play a part.

Spread through the bloodstream or lymphatic system

Although it's not known how, endometriosis cells are believed to get into the bloodstream or lymphatic system(the immune system network of vessels and glands).

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's believed some women's immune systems aren't able to fight off endometriosis effectively. Many women with endometriosis arefound to have lower immunity (resistance) to other conditions. However, this may be a result of the endometriosis, rather than the cause of the condition.

Environmental causes

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

However, while research suggests there's a link between endometriosis and high levels of dioxin exposure in animals,it's 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's this development that allows the human body to grow in the womb before birth.

It's been suggested some adult cells may retain this ability to change, and the shedding of menstrual blood into the pelvis during a period may stimulate them to transform into endometrial cells.

Content supplied by the NHS Website

Medically Reviewed by a doctor on 24 Nov 2016