There are different hypotheses as to what causes endometriosis. Unfortunately, none of these theories have ever been entirely proven, nor do they fully explain all the mechanisms associated with the development of the disease.

Thus, the cause of endometriosis remains unknown.

Most scientists working in the field of endometriosis do agree, however, that endometriosis is exacerbated by oestrogen. Subsequently, most of the current treatments for endometriosis attempt to temper oestrogen production in a woman’s body in order to relieve her of symptoms.

At the moment there are no treatments, which fully cure endometriosis.

Several theories have become more accepted, and reality is that it may be a combination of factors, which make some women develop endometriosis.


Metaplasia means to change from one normal type of tissue to another normal type of tissue. It has been proposed by some that endometrial tissue has the ability in some cases to replace other types of tissues outside the uterus.

Some researchers believe this happens in the embryo, when the uterus is first forming. Others believe that some adult cells retain the ability they had in the embryonic stage to transform into reproductive tissue.

Retrograde menstruation

This theory was promoted by Dr John Sampson in the 1920s. He surmised that menstrual tissue flows backwards through the fallopian tubes (called “retrograde flow”) and deposits on the pelvic organs where it seeds and grows.

However, there is little evidence that endometrial cells can actually attach to women’s pelvic organs and grow. Years later, researchers found that 90% of women have retrograde flow. But since most women don’t develop endometriosis, some doctors have concluded that something else (perhaps an immune system problem or hormonal dysfunction) may be the trigger for endometriosis.

The Retrograde Menstruation Theory also doesn’t explain how endometriosis develops in women who’ve had a hysterectomy or a tubal ligation nor why, in rare cases, men have developed endometriosis when they’ve been treated with oestrogen after prostate surgery.

Genetic disposition

It has been demonstrated that first-degree relatives of women with this disease are more likely to develop endometriosis. And when there is a hereditary link, the disease tends to be worse in the next generation.

There are ongoing worldwide studies investigating the blood samples from sisters with endometriosis in hopes of isolating an endometriosis gene.

This is what we know so far about genetics:

Lymphatic or vascular distribution

Endometrial fragments may travel through blood vessels or the lymphatic system to other parts of the body. This may explain how endometriosis ends up in distant sites, such as the lung, brain, skin, or eye.

Immune system dysfunction

Some women with endometriosis appear to display certain immunologic defects or dysfunctions. Whether this is a cause or effect of the disease remains unknown.

Environmental influences

Some studies have pointed to environmental factors as contributors to the development of endometriosis, specifically related to the way toxins in the environment have an effect on the reproductive hormones and immune system response, though this theory has not been proven and remains controversial.

See also

» FACTS about endometriosis published by the World Endometriosis Society and WERF

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