Electronic cigarettes (e-cigarettes), also known as electronic nicotine-delivery systems, are devices that produce an aerosol by heating a liquid that contains a solvent (vegetable glycerin, propylene glycol, or a mixture of these), one or more flavorings, and nicotine, although the nicotine may be omitted. The evaporation of the liquid at the heating element is followed by rapid cooling to form an aerosol. This process is fundamentally different from the combustion of tobacco, and consequently the composition of the aerosol from e-cigarettes and the smoke from tobacco is quite different. E-cigarette aerosol is directly inhaled (or “vaped”) by the user through a mouthpiece. Each device includes a battery, a reservoir that contains the liquid, and a vaporization chamber with heating element . The design of the e-cigarette was originally based on the design of conventional cigarettes but has since evolved, with later-generation devices permitting users to refill a single device with different liquids and to customize the heating element.
It is clear that the use of e-cigarettes has biologic effects and possibly health-related effects on persons who do not smoke conventional tobacco products. Although some studies suggest that smoking e-cigarettes may be less dangerous than smoking conventional cigarettes, more needs to be learned. A particular challenge in this regard is the striking diversity of the flavorings in e-cigarette liquids, since the effects on health of the aerosol constituents produced by these flavorings are unknown. At present, it is impossible to reach a consensus on the safety of e-cigarettes except perhaps to say that they may be safer than conventional cigarettes but are also likely to pose risks to health that are not present when neither product is used. Epidemiologic data indicate that e-cigarette use is growing among minors and young adults and may promote nicotine addiction in these age groups among those who would otherwise have been nonsmokers. More research is needed to understand the effectiveness of e-cigarettes as a smoking-cessation tool, to identify the health risks of e-cigarette use, and to make these products as safe as possible. Even as this research is under way, regulations that make e-cigarettes unavailable to children is warranted, as are public health initiatives that discourage nonsmokers from smoking conventional cigarettes or using e-cigarettes.