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The idea of nail polish as a risky substance gained traction in 2006 when public health advocates began a nationwide protest concerning three compounds — often referred to as “the toxic trio” — in leading nail polish brands.

The trio consisted of a known carcinogen, formaldehyde, used as a hardening agent, and two materials linked to developmental defects: toluene, to evenly suspend color, and the plasticizer dibutyl phthalate, or DBP, to add flexibility and sheen.

Since then, many companies have voluntarily removed these compounds from their products, although, as a 2012 investigation by the California Department of Toxic Substances Control found, some simply changed their labels while continuing to use them. While the European Union has banned the use of DBP in cosmetics, the United States Food and Drug Administration has not taken any comparable regulatory action.

Janet Nudelman, co-founder of the Campaign for Safe Cosmetics, an advocacy group, said the concern was that trace amounts of these materials would be absorbed through the skin or nail or that vapors would be inhaled. “No one is saying that occasional application of nail polish will cause long-term health consequences,” she said. But certain groups may be at higher risk.

Researchers have raised direct health concerns for those who work in nail salons, for instance, leading salon operators to organize for better regulation.

Children, too, may be particularly susceptible to phthalates like DBP that pose developmental risks, and some pediatricians now warn against letting young girls, especially those young enough to chew on their fingers, wear polish.

For dedicated polish enthusiasts, Ms. Nudelman recommends doing research to find the safest brands. The Environmental Working Group maintains a searchable cosmetics database at www.ewg.org/skindeep.