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If you've ever been within sniffing distance of someone slathering on nail polish, then you're more than familiar with the sickly sweet odor that can emanate from a single tiny bottle of varnish, a result of evaporating solvents wafting through the air.

One of these chemicals is toluene, a nervous-system toxin and Volatile Organic Compound that not only helps nail polish go on smoothly and adhere evenly to the nail, but is also used as an octane booster in gasoline fuels used in internal combustion engines. In addition to causing eye irritation, headaches, dizziness, and nausea, high amounts of toluene can also lead to birth defects, developmental abnormalities, along with liver and kidney damage. In fact, studies have noted an association between toluene exposure and an increased incidence of spontaneous abortions.

Because of concerns over the damaging health effects that toluene-as well as formaldehyde and dibutyl phthalate-could pose to nail salon workers and just about every other woman on the planet, the European Union banned all three from use in cosmetics in 2004.

No such luck in the U.S. of A.-remember, the U.S. Food and Drug Association doesn't require that cosmetics products be tested for safety before they are sold-although some states, such as California, have instituted laws requiring companies to declare the use of compounds that appear on the state's Proposition 65 list of chemicals known to cause cancer, birth defects, or reproductive harm.

Tip: Toluene may appear on ingredients labels as phenylmethane, methylbenzene, or toluol.

Difficulty level: Easy