Science and the evolving electronic cigarette.

OBJECTIVE: Electronic cigarettes (ECIGs) have continued to gain popularity among the general public since their introduction in 2003. While all ECIGs work by heating a liquid solution into an aerosol that is then inhaled by the user, there are differences in engineering characteristics and appearance of the devices as well as how the liquid is stored and heated, its nicotine concentration, its ratio of propylene glycol and/or vegetable glycerin, and the flavorants added to the liquid. Some of the research areas previously examined with ECIGs include aerosol toxicant yield, user puffing behavior, physiological effects, subjective effects, abuse liability, and effects on smoking cessation. CONCLUSION: Much of this work used earlier device models that delivered very little nicotine to the user, and additional research needs to be conducted using consistent and reliable devices, assays, and methodologies in order to gain a clearer understanding of ECIGs and their implications for individual and public health. Furthermore, the effects that ECIGs have on smoking cessation and among vulnerable populations must be addressed empirically.