Researchers say that two organochlorine pesticides lingering in the environment are associated with an increased risk of endometriosis.

In spite of being restricted or banned in the U.S. for several decades, two organochlorine pesticides continue to affect the health of younger women.

Researchers from the Fred Hutchinson Cancer Research Center and the University of Washington found that women exposed to these pesticides were more likely to have endometriosis. This painful condition occurs when the tissue lining the uterus grows outside the organ, and it affects more than five million American women.

In a new study, published today in the journal Environmental Health Perspectives, higher blood levels of either beta-hexachlorocyclohexane or mirex increased the risk of endometriosis by 30 to 70 percent in women ages 18 to 49.

Read More About Endometriosis Risks and Treatments »

Even though these pesticides were last used in the 1970s, it can take years for them to fully break down in the environment, which is why researchers continue to study their effects.

“Persistent environmental chemicals, even those used in the past, may affect the health of the current generation of reproductive age women,” says Kristen Upson, Ph.D., the lead study author and a postdoctoral fellow at the Epidemiology Branch of the National Institute of Environmental Health Sciences (NIEHS).

Previous research on the connection between endometriosis and these pesticides showed mixed results. However, the larger size of the current study—and the inclusion of women from the general population—allowed the researchers to better evaluate the dangers of these chemicals.

“Our findings for beta-hexachlorocyclohexane are similar to that of the prior, smaller population-based study of endometriosis,” says Upson. “The consistency of findings across population-based studies lends further support to the association between beta-hexachlorcyclohexane and endometriosis.”

In the current study, the other pesticide, mirex, showed up less frequently in women’s blood. This, the researchers write, makes it “unlikely to be a major contributor to endometriosis incidence” in the women in the study.

Other studies have found that organochlorine pesticides act similarly to the female hormone estrogen—a driving force behind endometriosis—further reinforcing the study results.

“Organochlorine pesticides have generally demonstrated estrogenic properties in [laboratory] studies and adverse reproductive effects in limited laboratory animal studies,” says Upson, “altering the function of the uterus, ovaries, and the body’s hormone production.”

Endometriosis occurs when the tissue that lines the uterus—or womb—grows in other places, such as the ovaries, fallopian tubes, or the lining of the pelvic cavity.

Women with endometriosis can experience chronic pain in the lower back and pelvis, very painful menstrual cramps, and infertility.

Discover Effective Home Remedies for Menstrual Cramps »

Reducing the risk of exposure to other chemicals—such as BPA, which is found in certain plastics—is often as simple as not using products that contain it. But because organochlorine pesticides are so widespread in the environment, avoiding them is much more difficult.

“There are certain foods, like dairy products,” says Caroline Cox, research director for the Center for Environmental Health, “where even though we haven’t used these chemicals in a pretty long time, they’re still the most commonly detected thing in that particular food.”

Organochlorine pesticides are chemically similar to fats, so they tend to accumulate in high-fat foods, especially animal products. Changing your diet, then, is one of the best ways to avoid them.

Learn More About 5 Hidden Household Dangers »

“The most common advice is to trim the fatty parts of meat off before you eat it,” says Cox. “As far as milk, you can switch to low-fat or non-fat products, rather than using the full-fat version.”

Because animal products tend to have higher levels of organochlorine pesticides, switching to a vegetarian diet can also reduce your exposure to these chemicals. If that’s too extreme, says Cox, you can try skipping meat once a week, such as on “Meatless Monday.”