E-cigarettes heat a mix of chemicals, called an e-liquid, to produce an aerosol that is inhaled by the user. E-cigarettes expose users and those close by to a variety of chemicals, many of which have specific health concerns.
18.5.2.1 E-liquids
E-liquids used in e-cigarette devices vary in their contents, mostly due to the wide variety in flavouring chemicals mixed to create e-liquid flavours. E-liquids usually contain numerous flavouring chemicals, solvents and coolants, and some contain nicotine and/or other drugs, such as those derived from cannabis.1 Some e-liquids contain naturally extracted tobacco liquids (NET liquids) mixed with other chemicals.2 See Section 18.5.3 for the chemical “ingredients” in e-liquids and Section 18.5.4 for the toxicity concerns with these chemicals.
18.5.2.2 Aerosol emissions from e-cigarettes
The emissions from an e-cigarette are an aerosol, consisting of tiny droplets of chemicals that float in gases, as described for tobacco in Section 12.4.1.1. Tobacco smoke is also an aerosol, but the types and amounts of the chemicals in tobacco emissions differ to those in e-cigarette emissions.1
E-cigarettes produce aerosol particles in similar numbers and sizes to those produced by conventional cigarettes. E-cigarette aerosol particles are typically between 11 nm and 560 nm in diameter;1,3-5 a particle size that is expected to be deposited in the small airways and alveoli (air sacs) of the lungs.1 Modelling studies predict that billions of e-cigarette aerosol particles would be deposited throughout the airways after a single two-second puff, more than double the number for conventional cigarettes, with deposition primarily in the alveoli.5,6 One study has estimated the proportion of particle deposition in specific regions of the airways as 45–60% in the alveolar region, 10–25% in the tracheobronchial region, and 20-35% in the extrathoracic region (nose, mouth, throat and voice box).7
Mainstream e-cigarette emissions are those that are drawn by the user and inhaled. Aerosols that are exhaled by the user potentially expose non-users to chemicals in the secondhand e-cigarette aerosol. Unlike cigarettes and other tobacco products that are lit, e-cigarettes produce minimal side-stream emissions (described in Section 12.4.1.2 for tobacco smoke), so secondhand aerosols mostly consist of those exhaled from users. There is conclusive evidence that e-cigarette use results in increased airborne particulate matter pollution in indoor environments.8 Significant increases in propylene glycol, glycerol, nicotine and volatile organic compounds (VOCs) have been detected after indoor e-cigarette use.1
A study comparing fresh and aged (up to 2 hours) e-cigarette aerosols showed that interactions of the particles with the indoor pollutant ozone (O3) resulted in higher levels of ultrafine particles and toxic carbonyl compounds in the aged aerosols.9 Other toxic molecules have been found to accumulate with ageing of e-cigarette aerosols, such as reactive and oxygenated species.10 These results indicate a potential health risk from inhaling secondhand e-cigarette aerosols.
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References
1. National Industrial Chemicals Notification and Assessment Scheme (NICNAS). Non-nicotine liquids for e-cigarette devices in Australia: chemistry and health concern. Australian Government Department of Health, 2019. Available from: https://www.industrialchemicals.gov.au/sites/default/files/2020-08/Non-nicotine%20liquids%20for%20e-cigarette%20devices%20in%20Australia%20chemistry%20and%20health%20concerns%20%5BPDF%201.21%20MB%5D.pdf.
2. Farsalinos KE, Gillman IG, Melvin MS, Paolantonio AR, Gardow WJ, et al. Nicotine levels and presence of selected tobacco-derived toxins in tobacco flavoured electronic cigarette refill liquids. International Journal of Environmental Research and Public Health, 2015; 12(4):3439-52. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25811768
3. Ingebrethsen BJ, Cole SK, and Alderman SL. Electronic cigarette aerosol particle size distribution measurements. Inhal Toxicol, 2012; 24(14):976-84. Available from: https://www.ncbi.nlm.nih.gov/pubmed/23216158
4. Mikheev VB, Brinkman MC, Granville CA, Gordon SM, and Clark PI. Real-time measurement of electronic cigarette aerosol size distribution and metals content analysis. Nicotine & Tobacco Research, 2016; 18(9):1895-902. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27146638
5. Manigrasso M, Buonanno G, Fuoco FC, Stabile L, and Avino P. Aerosol deposition doses in the human respiratory tree of electronic cigarette smokers. Environmental Pollution, 2015; 196:257-67. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25463721
6. Manigrasso M, Buonanno G, Stabile L, Morawska L, and Avino P. Particle doses in the pulmonary lobes of electronic and conventional cigarette users. Environmental Pollution, 2015; 202:24-31. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25796074
7. Kapiamba KF, Achterberg S, Lin TC, Whitefield PD, Huang YW, et al. Characterizing the transient emission of particles and gases from a single puff of electronic cigarette smoke. Chemical Research in Toxicology, 2025; 38(2):270-80. Available from: https://www.ncbi.nlm.nih.gov/pubmed/39818726
8. Banks E, Yazidjoglou A, Brown S, Nguyen M, Martin M, et al. Electronic cigarettes and health outcomes: systematic review of global evidence. Report for the Australian Department of Health, 2022, National Centre for Epidemiology and Population Health: Canberra. Available from: https://www.nhmrc.gov.au/sites/default/files/documents/attachments/ecigarettes/Electronic_cigarettes_and_health_outcomes_%20systematic_review_of_evidence.pdf.
9. Tian L, Woo W, and Lin YH. Chemical transformation of vaping emissions under indoor atmospheric aging processes. Chemical Research in Toxicology, 2025; 38(2):260-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/39832792
10. Woo W, Tran LN, Tian L, Canchola A, and Lin YH. Dynamic chemistry and toxicity of e-cigarette aerosols and their product waste. Chemical Research in Toxicology, 2026; 39(3):253-66. Available from: https://www.ncbi.nlm.nih.gov/pubmed/41678326