E-cigarettes are battery-powered devices that generate an inhalable aerosol that usually contains nicotine. They are designed as alternatives to traditional cigarettes.Millions of teens and young adults now use e-cigarettes. In 2019, nearly 28% of high-school students and 11% of middle-school students reported using e-cigarettes. About 8% of adults ages 18 to 24 reported using them in 2018.E-cigarettes are relatively new, and their long-term effects are not yet known. Although they may potentially be less harmful substitutes for traditional cigarettes, risks of addiction, injury, and death from e-cigarettes are becoming more apparent.Examples of types of e-cigarettesGraphic showing vape pens, pod-modsWith millions of teens and young adults using e-cigarettes, a new generation could become addicted to nicotine and face other health risks. For some adult smokers, e-cigarettes may offer a less harmful substitute for traditional cigarettes. However, long-term effects on users, second-hand exposure, and environmental effects are not yet fully known.What is it? Electronic cigarettes—or e-cigarettes—are battery-powered devices that convert a liquid, usually with nicotine, into an inhalable aerosol. They are designed as an alternative to smoking traditional cigarettes. First introduced in the United States about 15 years ago, e-cigarettes have evolved from disposable, single-use products to more sophisticated devices that can be refilled and customized (fig. 1).Figure 1. E-cigarettes can vary widely in design and appearance.E-cigarettes are popular among teens and young adults, according to the Centers for Disease Control and Prevention (CDC). In 2019, nearly 28 percent of high-school students and 11 percent of middle-school students reported using e-cigarettes. About 8 percent of young adults ages 18 to 24 reported using e-cigarettes in 2018.How does it work? Although e-cigarettes vary in design and appearance, they generally work the same way. An e-cigarette has four components: battery, cartridge or tank that holds a liquid, heating element or atomizer, and mouthpiece. Studies have identified a wide variety of chemicals in the cartridges, liquids, and aerosols, including between 60 and 113 ingredients in different liquid brands. According to CDC, the aerosol from the liquid generally contains fewer harmful chemicals than smoke from traditional cigarettes. However, risks of injury and death from e-cigarettes are becoming more apparent, and the toxicity of some ingredients in inhaled form is largely unknown.The liquid typically contains water and other solvents, nicotine, flavoring, and other substances. The liquid can also contain tetrahydrocannabinol (THC), the main psychoactive chemical in marijuana. The aerosol can contain metals, volatile organic compounds, and formaldehyde, which is a known carcinogen.The device heats the liquid, creating an aerosol. Inhalation, commonly called vaping, deposits particles in the user’s lungs (fig.