May 11, 2012 -- Certain chemicals that are widely used in sunscreens and other products because they protect against UV light are associated with an increased risk of developing the gynecological condition endometriosis, a new study shows.
But the Personal Care Products Council, a group that represents cosmetics manufacturers, called the study "weak" and "unconvincing" and said it shouldn't scare people away from safe sun practices, including sunscreen use.
Sunscreen Ingredient May Mimic Estrogen
The study, which is published in Environmental Science & Technology, measured concentrations of five kinds of chemicals called benzophenones in the urine of more than 600 women who were evaluated for endometriosis.
Benzophenones are used in a variety of products because they protect against UV light. In small amounts, that helps to stabilize the formulations of products that are stored in clear containers, like nail polish. At higher concentrations, and when they are applied to the skin, they are powerful sunscreens.
Endometriosis is a painful condition that occurs when tissue from the inside of the uterus grows outside of the uterus. When this tissue grows in other parts of the body, typically spilling into the abdomen around the ovaries or fallopian tubes, it behaves as if it were still in the uterus, thickening and shedding each month in sync with a woman's menstrual cycle. Endometriosis can lead to scarring and infertility.
Studies estimate that about 1 in 10 women have the condition, and some research suggests that it is becoming more common.
Benzophenones are easily absorbed through the skin. Studies by the CDC have found benzophenones in the urine of 97% of people tested.
Scientists are concerned about benzophenones because the body may mistake them for hormones.
"These compounds are estrogenic. They mimic estrogen in the body," says researcher Kurunthachalam Kannan, PhD, a professor of public health and environmental health sciences with the New York State Department of Health's Wadsworth Center in Albany.
Kannan says benzophenone-3, which appears on sunscreen labels as oxybenzone, is even more strongly estrogenic than bisphenol-A (BPA), a chemical found in certain plastics that's recently been the subject of regulatory scrutiny.
The cause of endometriosis is not known, but the condition is fed by the female hormone estrogen. Treatment sometimes involves taking medications that lower estrogen levels.
Study Ties Benzophenones to Endometriosis
Overall, the study found that only one kind of benzophenone, a chemical known as benzophenone-1, was significantly associated with the risk that a woman would have endometriosis.
Women with the highest amounts of benzophenone-1 in their urine had a 65% greater chance of having endometriosis compared to women with the lowest levels.
Benzophenone-1 is a chemical additive that's mostly used in nail polishes, according to the cosmetics industry web site CosmeticsInfo.org, but it also forms when the body breaks down oxybenzone, the major ingredient in sunscreen.
"We find it to be a very weak study and quite unconvincing," says Linda Loretz, PhD, director of safety and regulatory toxicology for the Personal Care Products Council, a group that represents the interests of the cosmetics industry.
Loretz points out that researchers had no information about whether the women used sunscreen or how much they used, which makes it impossible to know how they were exposed to the chemicals.
"I don't think consumers should be concerned," she says. "I think safe sun practices are much more important."
Women in the study who lived in California had higher benzophenone concentrations in their urine if they were tested during the summer months.
That suggests that sunscreen is playing a role in exposure, says Sonya Lunder, MPH, a senior analyst with the Environmental Working Group (EWG) in Washington, D.C.
A separate study by the CDC also found "higher concentrations in lighter-skinned people and also in the summertime, which points to the role of sunscreen in the measurement in our bodies," Lunder says.
The Environmental Working Group publishes its own guide to sunscreen safety, and they have flagged oxybenzone, a chemical that's found in half of all sunscreens, as an ingredient that people should avoid.
"We have raised concerns about it over the past couple of years as these kinds of studies come out -- our concern level matches up with it," Lunder tells WebMD.
"The studies in people are still pretty small, pretty limited, but they are backed up by a series of laboratory studies finding that this chemical and this whole family of chemicals, really, has estrogenic effects," she says.
In addition to acting like estrogen in the body, Lunder says many people are simply sensitive to oxybenzone and that it can cause skin irritation.
The EWG says safer sunscreens are those that are mineral-based with ingredients zinc oxide or titanium dioxide as natural UV blockers.