Electronic cigarettes (e-cigarettes) are portable devices that deliver nicotine through the battery-powered vaporization of a solution of nicotine, propylene glycol, vegetable glycerin, and flavor chemicals. They are sometimes introduced as harmless or safer alternatives to conventional cigarettes. Although e-cigarettes deliver nicotine without the thousands of toxic substances contained in conventional cigarettes,
1,2 the nicotine content of e-cigarettes can lead to addiction. It is unclear whether e-cigarettes are safer than conventional cigarettes because the toxic effects of e-cigarette components are not fully understood.