Electronic cigarettes: what are they and what do they do?

Abstract

Electronic cigarettes (ECIGs) use electricity to power a heating element that aerosolizes a liquid containing solvents, flavorants, and the dependence-producing drug nicotine for user inhalation. ECIGs have evolved rapidly in the past 8 years, and the changes in product design and liquid constituents affect the resulting toxicant yield in the aerosol and delivery to the user. This rapid evolution has been accompanied by dramatic increases in ECIG use prevalence in many countries among adults and, especially, adolescents in the United States. The increased prevalence of ECIGs that deliver nicotine and other toxicants to users' lungs drives a rapidly growing research effort. This review highlights the most recent information regarding the design of ECIGs and their liquid and aerosol constituents, the epidemiology of ECIG use among adolescents and adults (including correlates of ECIG use), and preclinical and clinical research regarding ECIG effects. The current literature suggests a strong rationale for an empirical regulatory approach toward ECIGs that balances any potential ECIG-mediated decreases in health risks for smokers who use them as substitutes for tobacco cigarettes against any increased risks for nonsmokers who may be attracted to them.

Keywords: electronic cigarette; review; tobacco control.

Figure 1

Examples of open and closed electronic cigarette systems.

Figure 2

Parts of an open electronic cigarette system.

Figure 3

Current (past 30 days) ECIG use trends among U.S. adults, high school students, and middle school students.^,,,

Figure 4

Mean (+ SEM) plasma nicotine concentration from different human laboratory studies and different products with blood sampled before and immediately after a 10-puff product use bout. Combustible cigarette data are from 32 tobacco cigarette smokers using their usual brand of combustible cigarette. ECIG A is a “cigalike” product called “Blu” loaded with two different concentrations of liquid nicotine (16 or 24 mg/mL, both containing 20% propylene glycol and 50% vegetable glycerin). Data are from 23 tobacco cigarette smokers with 7 days experience with the product. ECIG B is a “cigalike” product called “V2cigs” and ECIG C is a “tank” product called “EVIC” with an “EVOD” heating element; both were loaded with an 18 mg/mL liquid containing 34% propylene glycol and 66% vegetable glycerin. Data are from 23 experienced electronic cigarette users. ECIG D is a 3.3-V “Ego” battery fitted with a 1.5-Ω dual-coil cartomizer (“Smoktech”) and filled with ~1 mL of a 70% propylene glycol/30% vegetable glycerin liquid that varied by liquid nicotine concentration (0, 8, 18, or 36 mg/mL). Data are from 16 experienced electronic cigarette users. Taken together, the figure shows the wide variability of nicotine delivery in marketed electronic cigarettes, many of which underperform a combustible tobacco cigarette, but some of which can, in the hands of experienced users, exceed the nicotine delivery of a combustible tobacco cigarette, depending on the liquid nicotine concentration.