Table 1.

Major toxic constituents in e-cigarettes

1. Nicotine     - Reaches brain within 15 s after puff on a CC, likely similar with EC use—creates immediate pleasurable effects that reinforce use     - Not alone thought to be a human carcinogen     - Activates the sympathetic nervous system—thought to be associated with risk of myocardial ischemia, arrythmias, cardiac tissue remodeling, thrombogenesis, and endothelial dysfunction     - Comparison to CCs: Degree of exposure to nicotine varies considerably depending on device characteristics, e-liquids, and how ECs are used 2. Humectants—EC liquids usually contain propylene glycol and glycerol as solvent carriers to generate aerosols     - When overheated both humectants decompose into toxic carbonyl compounds     - Additionally, inhaled propylene glycol at concentrations in ECs can cause eye and throat irritation 3. Flavorings—dozens of flavoring compounds have been used in ECs (e.g., menthol, benzaldehyde, vanillin, diacetyl)     - These compounds are generally considered safe as food additives. The effects of inhaled flavoring compounds on the pulmonary system are less clear     - Flavorings have been found to form aldehydes and other respiratory irritants when heated

4. Carbonyl compounds—e.g., formaldehyde, acetaldehyde, acrolein     - Generated by the heating of humectants and flavorings in e-liquids, particularly in devices with battery power greater than 3 V     - Known to be carcinogenic and respiratory irritants     - Comparison to CCs: Under typical use, exposure to toxic carbonyls in ECs appears significantly less than with CC use. 5. Metals—lead, nickel, chromium, manganese, aluminum, tin, and iron have been found in EC emissions     - Originate from the heating coil or other device parts, such as wires, joints, or batteries     - Metal levels vary considerably across products and studies and are theoretically toxic to multiple organ systems.     - Comparison to CCs: Limited evidence suggests that metal exposure is greater in ECs than CCs, except for cadmium which is markedly higher in CCs.

National Academies of Sciences, Engineering, and Medicine. Public health consequences of e-cigarettes. The National Academies