The chemical components of e-cigarettes are diverse and complex. Here's a summary of the key components identified in both e-liquids and aerosols:

1. Solvent Carriers: The primary solvents in e-liquids are propylene glycol (PG) and glycerol (GLY), also known as vegetable glycerin. These are used to produce aerosols that simulate tobacco cigarette smoke and are found in varying mixing ratios .

2. Nicotine: E-liquids can contain nicotine in varying concentrations, depending on whether they are nicotine-containing or nicotine-free .

3. Flavor Compounds: A wide variety of flavor compounds are added to e-liquids to provide different tastes. These can include traditional tobacco and menthol flavors, as well as those resembling fruits, desserts, nuts, spices, candy, and beverages .

4. Tobacco-Specific Nitrosamines (TSNAs): These are found in both e-liquids and aerosols and are harmful or potentially harmful constituents .

5. Aldehydes: These are generated during the vaporization process and can include formaldehyde, acetaldehyde, and other carbonyl compounds .

6. Metals: Trace elements such as chromium, nickel, and lead have been detected in e-cigarette aerosols .

7. Volatile Organic Compounds (VOCs): A range of VOCs, including benzene and toluene, can be present in e-cigarette emissions .

8. Phenolic Compounds: These can be part of the e-liquid and aerosol composition, affecting taste and potentially impacting health .

9. Polycyclic Aromatic Hydrocarbons (PAHs): These are found in both e-liquids and aerosols and are known carcinogens .

10. Heavy Metals: E-cigarette aerosols may contain heavy metals such as antimony and copper .

11. Tobacco Alkaloids: Besides nicotine, other tobacco alkaloids like nicotine-N'-oxides, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), and N-Nitrosonornicotine (NNN) have been identified in e-cigarettes .

12. Drugs: Illicit drugs such as cannabis, synthetic cannabinoids, and other substances have been found in some e-liquid formulations .

It's important to note that the composition of e-cigarette aerosols can differ from that of e-liquids due to chemical reactions and thermal decomposition that occur during the heating process, potentially leading to the formation of new compounds . The presence of these chemicals raises concerns about the safety of e-cigarettes, particularly regarding long-term health effects and the potential for addiction, especially among youth .