The wide range of e-cigarette device types is described in detail in Section 18.1.1.
18.5.6.1 Effects of different device settings
E-cigarettes generally use battery power to heat a metal coil that heats the e-liquid, forming an aerosol that is inhaled by the user. E-cigarette devices such as box mods and pod mods are highly customisable, with the ability to change power settings, temperature and airflow. The temperature of the heating element varies between devices and when different settings are used. Heating element temperatures range between approximately 150°C to 350°C under typical usage conditions.1 Chemical exposure from e-cigarette aerosols is affected by the power output, temperature of the heated coil and the airflow settings on the device. An increase in temperature can increase the presence of harmful free radicals, carbonyl compounds and benzene produced, as well as some metals in the emissions.2 Increasing the power settings also increased toxic emissions3 and damaging ‘free radical’ compounds in human bronchial cells exposed to e-cigarette aerosols in laboratory experiments.4
The resistance of the coil used to heat the e-liquid can vary. Low coil resistance allows more electrical current from the battery to pass through the coil and heat the e-liquid. This “sub-ohm” mode of use can change the levels of toxic chemicals in the emissions.5
While the nicotine yield (milligrams of nicotine in the smoke from one cigarette) is a useful measure of nicotine exposure from cigarettes, yield is less relevant for e-cigarettes as the same device or e-liquid mix may be used in multiple sessions, over many days or even weeks. Nicotine delivery for these devices can be measured as nicotine flux: the amount of nicotine delivered per second of use.6 Higher power settings and higher e-liquid concentrations will produce a higher nicotine flux. A study measuring nicotine flux of multiple devices found a nicotine flux range of 3.7 to 110 mg/sec with a mean of 29 mg/sec nicotine.6 With new e-cigarette devices regularly entering the market, the nicotine flux has increased over time. By 2019, nearly 40% of e-cigarettes had a nicotine flux of over 60 mg/sec.6
The toxic gas carbon monoxide was detected at low levels in e-cigarette aerosols when high power settings were used.7 Under maximal power (200W) and 4-second puff conditions, the carbon monoxide concentration in aerosols was detected at over 180 ppm, a concentration that exceeds the US National Ambient Air Quality Standards for outdoor carbon monoxide concentration (35 ppm for 1 hour). Lower power settings are recommended by the authors of this study to reduce the risk from inhaling carbon monoxide.7
Under some conditions, a low supply of e-liquid reaches the heating coil leading to an unpleasant user experience called a ‘dry puff’. Dry puff conditions lead to an increased concentration of carbonyls such as formaldehyde in the aerosols.8 If dry puff conditions were always used, this could lead to intake of formaldehyde at much higher levels than cigarettes. However, these conditions produce a taste that is aversive and therefore likely avoided by users.
A novel e-cigarette device type (ultrasonic cigarette or u-cigarette) that converts e-liquids into aerosols using sonic vibration rather than a heating coil was examined by independent researchers. They concluded that the concentrations of nicotine, aldehydes and other chemicals, as well as the toxic effect of the aerosols on cells grown in the laboratory, provide no evidence that the aerosols from u-cigarettes are less harmful than those from e-cigarettes.9
18.5.6.2 Effects of different user modes
E-cigarettes can be used in different manners. Mouth-to-lung (MTL) use involves inhaling into the mouth in one motion then into the lungs in a second motion. This action is similar to smoking a cigarette. MTL use is more common for disposable devices.
Direct-to-lung (DTL) use involves inhaling directly into the lungs one long inhalation.2 Breathing out these emissions may be referred to as cloud chasing. According to e-cigarette companies, more customisable devices that allow airflow control, or those with low resistance coils to allow more electrical current, are more commonly used for DTL mode of use. Lower nicotine concentrations are suggested for DTL use. Restricted direct-to-lung (RDL) use is described as a middle ground between MTL and DTL. The high surface area of the lungs means that direct-to-lungs use leads to a higher amount of exposure to the chemicals.2 However, DTL e-liquid mixes are usually less concentrated to compensate for this. There is some evidence that slow, deep inhalation and prolonged breath-holding increase particle transport into the small airways and alveoli and may increase the risk of inflammation and damage to the lungs.10
The concentration of toxic carbonyl compounds in the aerosols may be increased during dripping (adding e-liquid directly to the heating coil) and ‘squonking’ (where an inbuilt squeeze bottle is used to add e-liquid to the heating coil). This effect may be due to an increase in the temperature of the coil.8
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References
1. Chen W, Wang P, Ito K, Fowles J, Shusterman D, et al. Measurement of heating coil temperature for e-cigarettes with a "top-coil" clearomizer. PLoS One, 2018; 13(4):e0195925. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29672571
2. Korzun T, Lazurko M, Munhenzva I, Barsanti KC, Huang Y, et al. E-cigarette airflow rate modulates toxicant profiles and can lead to concerning levels of solvent consumption. ACS Omega, 2018; 3(1):30-6. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29399647
3. Fazeli E, Martinez B, Son Y, and Khlystov A. Flavoring compound chemical class and vaping conditions determine toxic carbonyl emissions from e-cigarettes. Chemistry Research in Toxicology, 2026; 39(3):329-38. Available from: https://www.ncbi.nlm.nih.gov/pubmed/41649144
4. Dusautoir R, Zarcone G, Verriele M, Garcon G, Fronval I, et al. Comparison of the chemical composition of aerosols from heated tobacco products, electronic cigarettes and tobacco cigarettes and their toxic impacts on the human bronchial epithelial BEAS-2B cells. Journal of Hazardous Materials, 2021; 401:123417. Available from: https://www.ncbi.nlm.nih.gov/pubmed/32763707
5. Effah F, Shaikh SB, Chalupa D, Faizan MI, Elder A, et al. High-resistance coils in E-cigarettes increase heavy metals leaching into aerosols to cause oxidants generation in human bronchial epithelial cells at air-liquid interface: A unique non-animal methodological approach on vaping studies. NAM J, 2025; 1. Available from: https://www.ncbi.nlm.nih.gov/pubmed/41614208
6. El Hourani M, Shihadeh A, Talih S, Eissenberg T, and Group CNFW. Comparison of nicotine emissions rate, 'nicotine flux', from heated, electronic and combustible tobacco products: data, trends and recommendations for regulation. Tobacco Control, 2022. Available from: https://www.ncbi.nlm.nih.gov/pubmed/35086911
7. Casebolt R, Cook SJ, Islas A, Brown A, Castle K, et al. Carbon monoxide concentration in mainstream E-cigarette emissions measured with diode laser spectroscopy. Tobacco Control, 2020; 29(6):652-5. Available from: https://www.ncbi.nlm.nih.gov/pubmed/31771993
8. Farsalinos KE, Voudris V, and Poulas K. E-cigarettes generate high levels of aldehydes only in 'dry puff' conditions. Addiction, 2015; 110(8):1352-6. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25996087
9. Omaiye EE, Luo W, McWhirter KJ, and Talbot P. Ultrasonic cigarettes: chemicals and cytotoxicity are similar to heated-coil pod-style electronic cigarettes. Chemistry Research in Toxicology, 2024; 37(8):1329-43. Available from: https://www.ncbi.nlm.nih.gov/pubmed/39051826
10. Sharma S, Meister M, He X, Wilson M, Zhang Q, et al. Puffing topography: a tool to evaluate vaping behavior and exposure risks. Inhal Toxicol, 2025; 37(9-10):439-50. Available from: https://www.ncbi.nlm.nih.gov/pubmed/40644519