E-cigarettes are increasingly popular battery-operated devices marketed as a safer alternative to smoking conventional cigarettes. They produce flavored nicotine aerosol that looks and feels like tobacco smoke but without the tar or other chemicals produced by burning tobacco leaves. However, while e-cigarettes do not produce tobacco smoke, it is still unclear how safe they are. They still deliver nicotine, which is a highly addictive drug. Also, vapor from some e-cigarette products has been found to contain known carcinogens and toxic chemicals.