Endometriosis is a condition in which tissue, resembling that which normally lines the uterus, grows outside the uterus and forms lesions. These lesions swell with each menstrual cycle but cannot leave the body through menstrual bleeding during that monthly cycle, causing inflammation and pain.

While the exact cause of endometriosis is not known, researchers think a combination of factors is likely to play a role. Because endometriosis is more frequent in some families than in others, the condition seems to have a genetic component. However, the development of the condition cannot be explained by genetics alone, and environmental factors may be involved.

Dioxins

Dioxin, an environmental pollutant, is the short name for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The term dioxin is also used when referring to “dioxin-like” polychlorinated biphenyls (PCBs), which have similar chemical and structural properties.

PCBs are used in transformers, capacitors, and coolers. Because of their known toxic effects on the human body and on the environment, PCBs were banned in the U.S. in 1976, but they persist in the air, water, and soil. Human exposure mainly occurs through the consumption of fish (including shellfish), meat, and dairy products.

Dioxins can disrupt the workings of the endocrine system (glands that produce hormones), affecting the hormonal balance in the body. Because hormones such as estrogen promote the growth of endometrial lesions, dioxins may be associated with an increased risk of endometriosis.

Dose-escalation studies in animals have shown that exposure to TCDD favors the spontaneous development of endometriosis in a dose-dependent manner. It also promotes the growth and survival of endometrial lesions.

Studies in people, however, have not been able to confirm a link between dioxin (TCDD) exposure and endometriosis risk.

Organochlorine pesticides

Organochlorine pesticides (OCPs) were widely used as insecticides in the mid-20th century. They are known to be a threat to human health, and most OCPs are now banned in both in the U.S. and Europe. Despite this, OCPs (like dioxins) are still found in fish and dairy products because they accumulate in organisms and persist in the food chain. They are also still in use elsewhere.

OCPs are known to have hormonal properties that are similar to estrogen. Because endometrial lesions depend on estrogen, researchers suspect that high exposure to OCPs through the environment can be a risk factor for endometriosis.

A study, published in 2013, measured the concentration of OCPs in the blood of 248 women with endometriosis. Its findings supported a link between high concentrations of two OCPs — β-hexachlorocyclohexane (β-HCH) or mirex — and an increased risk of endometriosis. The association was strongest between β-HCH and ovarian endometriosis.

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