The chemical composition of the electronic cigarette aerosol varies across and within manufacturers. Limited data exists regarding their chemistry. However, researchers at Johns Hopkins University analyzed the vape clouds of popular brands such as Juul and Vuse, and found "nearly 2,000 chemicals, the vast majority of which are unidentified."
The aerosol of e-cigarettes is generated when the e-liquid comes in contact with a coil heated to a temperature of roughly within a chamber, which is thought to cause pyrolysis of the e-liquid and could also lead to decomposition of other liquid ingredients. The aerosol (mist) produced by an e-cigarette is commonly but inaccurately called vapor. E-cigarettes simulate the action of smoking, but without tobacco combustion. The e-cigarette aerosol looks like cigarette smoke to some extent. E-cigarettes do not produce aerosol between puffs. The e-cigarette aerosol usually contains propylene glycol, glycerin, nicotine, flavors, aroma transporters, and other substances. The levels of nicotine, tobacco-specific nitrosamines (TSNAs), aldehydes, metals, volatile organic compounds (VOCs), flavors, and tobacco alkaloids in e-cigarette aerosols vary greatly. The yield of chemicals found in the e-cigarette aerosol varies depending on, several factors, including the e-liquid contents, puffing rate, and the battery voltage.
Metal parts of e-cigarettes in contact with the e-liquid can contaminate it with metals. Heavy metals and metal nanoparticles have been found in tiny amounts in the e-cigarette aerosol. Once aerosolized, the ingredients in the e-liquid go through chemical reactions that form new compounds not previously found in the liquid. Many chemicals, including carbonyl compounds such as formaldehyde, can inadvertently be produced when the nichrome wire (heating element) that touches the e-liquid is heated and chemically reacted with the liquid. Propylene glycol-containing liquids produced the most amounts of carbonyls in e-cigarette vapors, while in 2014 most e-cigarettes companies began using water and glycerin instead of propylene glycol for vapor production.
Propylene glycol and glycerin are oxidized to create aldehydes that are also found in cigarette smoke when e-liquids are heated and aerosolized at a voltage higher than 3 V. Depending on the heating temperature, the carcinogens in the e-cigarette aerosol may surpass the levels of cigarette smoke. Reduced voltage e-cigarettes generate very low levels of formaldehyde. A Public Health England (PHE) report found "At normal settings, there was no or negligible formaldehyde release." However, this statement was contradicted by other researchers in a 2018 study. E-cigarettes can emit formaldehyde at high levels (between five and 15 times higher than what is reported for cigarette smoke) at moderate temperatures and under conditions that have been reported to be non-averse to users. As e-cigarette engineering evolves, the later-generation and "hotter" devices could expose users to greater amounts of carcinogens.
Use
Background
There is a debate on the composition, and the subsequent health burden, of tobacco smoke compared with electronic cigarette vapor. Tobacco smoke is a complex, dynamic and reactive mixture containing around 5,000 chemicals. In 2021, researchers at Johns Hopkins University analyzed the vape aerosols of popular brands such as Juul and Vuse, and found "nearly 2,000 chemicals, the vast majority of which are unidentified." E-cigarette vapor contains many of the known harmful toxicants found in traditional cigarette smoke, such as formaldehyde, cadmium, and lead, though usually at a reduced percentage.
There are substances in e-cigarette vapor that are not found in tobacco smoke. Researchers are part of the conflict, with some opposing and others supporting of e-cigarette use. The public health community is divided, even polarized, over how the use of these devices will impact the tobacco epidemic. Some proponents of e-cigarettes think that these devices contain merely "water vapour" in the e-cigarette aerosols, but this view is refuted by the evidence.
+ List of hazardous tobacco smoke components with their cancer and non-cancer inhalation risk values. Smoke component Cancer risk (mg m−3) Institute Non-cancer risk (mg m−3) Endpoint Institute 1,1,1-Trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) 0.0001 U.S. EPA 1,1-Dimethylhydrazine 2E-06 ORNL 1,3-Butadiene 0.0003 U.S. EPA 0.002 reproduction U.S. EPA 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) 0.00026 Cal EPA 2-Amino-3-methyl-9H-pyrido[2,3-b]indole (MeAaC) 2.9E-05 Cal EPA 2-Amino-3-methylimidazo[4,5-b]quinoline (IQ) 2.5E-05 Cal EPA 2-Amino-6-methyl[1,2-a:3′,2″-d]imidazole (GLu-P-1) 7.1E-06 Cal EPA 2-Aminodipyrido[1,2-a:3′,2″-d]imidazole (GLu-P-2) 2.5E-05 Cal EPA 2-Aminonaphthalene 2E-05 Cal EPA 2-Nitropropane Cal EPA 0.02 liver, focal vacuolization and nodules U.S. EPA 2-Toluidine 0.0002 Cal EPA 3-Amino-1,4-dimethyl-5H-pyrido [4,3-b]indole (Trp-P-1) 1.4E-06 Cal EPA 3-Amino-1-methyl-5H-pyrido[4,3-b]-indole (Trp-P-2) 1.1E-05 Cal EPA 4-Aminobiphenyl 1.7E-06 Cal EPA 5-Methylchrysene 9.1E-06 Cal EPA 7H-Dibenzo(c,g)carbazole 9.1E-06 Cal EPA 2-Amino-9H-pyrido[2,3-b]indole (AaC) 8.8E-05 Cal EPA Acetaldehyde 0.0045 U.S. EPA 0.009 nasal olfactory epithelial lesions U.S. EPA Acetamide 0.0005 Cal EPA Acetone 30 neurological effects ATSDR Acetonitrile 0.06 mortality U.S. EPA Acrolein 2E-05 nasal lesions U.S. EPA Acrylamide 0.008 Acrylic acid 0.001 nasal olfactory epithelium degeneration U.S. EPA Acrylonitrile 0.00015 U.S. EPA 0.002 respiratory effects U.S. EPA Ammonia 0.1 respiratory effects U.S. EPA Aniline B2—probable human carcinogen U.S. EPA 0.001 immune-related U.S. EPA Arsenic 2.3E-06 U.S. EPA Benz[a]anthracene 9.1E-05 Cal EPA Benzene 0.0013 U.S. EPA 0.0098 decreased lymphocyte count ATSDR Benzo[a]pyrene 9.1E-06 Cal EPA Benzo[j]fluoranthene 9.1E-05 Cal EPA Beryllium 4.2E-06 Cadmium 5.6E-06 U.S. EPA Carbazole 0.0018 NATA Carbon disulfide 0.1 effects on CNS HC Carbon monoxide 10 cardiotoxic Cal EPA Chloroform 0.00043 U.S. EPA 0.1 liver changes ATSDR Chromium VI 8.3E-07 U.S. EPA 0.0001 lower respiratory effects U.S. EPA Chrysene 0.00091 Cal EPA Cobalt 0.0005 respiratory functions RIVM Copper 0.001 lung and immune system effects RIVM Di(2-ethylhexyl) phthalate 0.0042 Cal EPA Dibenzo[a,i]pyrene 9.1E-07 Cal EPA Dibenzo[a,h]acridine 9.1E-05 Cal EPA Dibenzo[a,h]anthracene 8.3E-06 Cal EPA Dibenzo[a,j]acridine 9.1E-05 Cal EPA Dibenzo[a,h]pyrene 9.1E-07 Cal EPA Dibenzo[a,l]pyrene 9.1E-07 Cal EPA Dibenzo[a,e]pyrene 9.1E-06 Cal EPA Dibenzo[c,g]carbazole 9.1E-06 Cal EPA Dimethylformamide 0.03 digestive disturbances; minimal hepatic changes U.S. EPA Ethyl carbamate 3.5E-05 Cal EPA Ethylbenzene 0.77 liver and kidney effects RIVM Ethylene oxide 0.00011 Cal EPA Ethylenethiourea 0.00077 Cal EPA Formaldehyde 0.00077 U.S. EPA 0.01 nasal irritation ATSDR Hexane 0.7 neurotoxicity U.S. EPA Hydrazine 2E-06 U.S. EPA 0.005 fatty liver changes ATSDR Hydrogen cyanide 0.003 CNS and thyroid effects U.S. EPA Hydrogen sulfide 0.002 nasal lesions U.S. EPA Indeno[1,2,3-c,d]pyrene 9.1E-05 Cal EPA Isopropylbenzene 0.4 increased kidney, adrenal gland weights U.S. EPA Lead 0.00083 Cal EPA 0.0015 not applicable U.S. EPA Manganese 5E-05 neurobehavioral U.S. EPA m-Cresol 0.17 CNS RIVM Mercury 0.0002 nervous system U.S. EPA Methyl chloride 0.09 cerebellar lesions U.S. EPA Methyl ethyl ketone 5 developmental toxicity U.S. EPA Naphthalene 0.003 nasal effects U.S. EPA N-nitrosodi-n-butylamine (NBUA) 6.3E-06 U.S. EPA N-nitrosodimethylamine (NDMA) 7.1E-07 U.S. EPA Nickel 9E-05 chronic active inflammation and lung fibrosis ATSDR Nitrogen dioxide 0.1 not applicable U.S. EPA N-nitrosodiethanolamine 1.3E-05 Cal EPA N-nitrosodiethylamine 2.3E-07 U.S. EPA N-nitrosoethylmethylamine 1.6E-06 Cal EPA N-Nitrosonornicotine (NNN) 2.5E-05 Cal EPA N-Nitroso-N-propylamine 5E-06 Cal EPA N-nitrosopiperidine 3.7E-06 Cal EPA N-nitrosopyrrolidine 1.6E-05 U.S. EPA n-Propylbenzene 0.4 increased organ weight U.S. EPA o-Cresol C- possible human carcinogen U.S. EPA 0.17 decreased body weight, neurotoxicity RIVM p-, m-Xylene 0.1 respiratory, neurological, developmental U.S. EPA p-Benzoquinone C- possible human carcinogen U.S. EPA 0.17 CNS RIVM p-Cresol C- possible human carcinogen U.S. EPA 0.17 CNS RIVM Phenol 0.02 liver enzymes, lungs, kidneys, and cardiovascular system RIVM Polonium-210 925.9 ORNL Propionaldehyde 0.008 atrophy of olfactory epithelium U.S. EPA Propylene oxide 0.0027 U.S. EPA Pyridine 0.12 odour threshold RIVM Selenium 0.0008 respiratory effects Cal EPA Styrene 0.092 body weight changes and neurotoxic effects HC Toluene 0.3 colour vision impairment ATSDR Trichloroethylene 82 HC 0.2 liver, kidney, CNS effects RIVM Triethylamine 0.007 n.a. U.S. EPA Vinyl acetate 0.2 nasal lesions U.S. EPA Vinyl chloride 0.0011 U.S. EPA
Particulate matter
Electronic cigarette aerosol contains fine and ultrafine particles of particulate matter, including particulate matter 2.5 μm or smaller in diameter (PM2.5). Studies have found that electronic cigarette aerosol can raise PM2.5 concentrations to several hundred micrograms per cubic meter (μg/m³), with measurements of 600–800 μg/m³ in vape shops and conventions and peak values exceeding 1,000 μg/m³; these levels are far above typical indoor backgrounds (8–52 μg/m³) and greatly exceed the World Health Organization’s 24‑hour PM2.5 guideline of 25 μg/m³ for outdoor air. PM2.5 is capable of penetrating deep into the lungs and entering the bloodstream, where it is associated with severe systemic inflammation, cardiovascular disease, and premature death.
Pathogens E-liquid used in e-cigarettes has been found to be contaminated with fungi and bacteria. Nicotine-containing e-liquids are extracted from tobacco that may contain impurities. Tobacco-specific impurities such as cotinine, nicotine-N'-oxides (cis and trans isomers), and beta-nornicotyrine are believed to be the result of bacterial action or oxidation during the extraction of nicotine from tobacco.
Re-used vapes, and vape sharing Bacterial pneumonia. Fungal pneumonia Viral pneumonia from vape sharing. SARS-CoV-2: Shared vaping devices are linked to COVID-19.
Chemicals E-cigarette components include a mouthpiece, a cartridge (liquid storage area), a heating element or atomizer, a microprocessor, a battery, and some of them have a LED light at the tip. They are disposable or reusable devices. Disposable ones are not rechargeable and typically cannot be refilled with a liquid. There is a diverse range of disposable and reusable devices, resulting in broad variations in their structure and their performance. Since many devices include interchangeable components, users have the ability to alter the nature of the inhaled vapor.
For the majority of e-cigarettes, many aspects are similar to their traditional counterparts, such as giving nicotine to the user. The use of an e-cigarette simulates the action of smoking, with a vapor that somewhat resembles cigarette smoke. E-cigarettes do not involve tobacco combustion, and they do not produce vapor between puffs. They do not produce sidestream smoke or sidestream vapor.
Vapor production basically entails preprocessing, vapor generation, and postprocessing. First, the e-cigarette is activated by pressing a button, or other devices switch on by an airflow sensor or other type of trigger sensor. Then, power is released to an LED, other sensors, and other parts of the device, and to a heating element or other kind of vapor generator. Subsequently, the e-liquid flows by capillary action to the heating element or other devices to the e-cigarette vapor generator. Second, the e-cigarette vapor processing entails vapor generation.