Question: How do electronic cigarettes produce the vapor inhaled by users of these products?
Answer: According to the cited reference, “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. (Dinakar C and O’Connor GT. The health effects of electronic cigarettes. 2016 NEJM 375:1372-1381)