In general, e-cigarettes often contain ingredients such as propylene glycol (PG) and glycerol, mixed with concentrated flavors and, optionally, a variable percentage of nicotine. Quantitative and qualitative studies have identified a wide variety of chemical components in the cartridges, refill solutions, and aerosols of e-cigarettes. Herrington and Myers (2015) have detected approximately 60 to 70 compounds (unidentified and identified) in each liquid tested, only varying by several constituents throughout the liquid. Kucharska and colleagues (2016) have identified 113 chemicals in 50 brands of liquids.

New Australian research has found most e-liquids contain chemicals known to cause respiratory issues and lung damage when inhaled. One study, published in The Medical Journal of Australia, found most e-liquids contained chemicals known to cause respiratory issues and lung damage when inhaled. Most contained ingredients that have since been banned by Australia’s drug regulator, the Therapeutic Goods Administration (TGA).   The study also found that most of the e-liquids also contained ‘2-aminooctanoic acid, which is an amino acid found in the biological products of mammals, including faeces, urine and blood. Its presence was potentially a result of contamination with one of these substances during the manufacturing or packaging processes.
 

Substances identified in e-cigarette liquids and aerosols include nicotine, solvent carriers (PG and glycerol), tobacco-specific nitrosamines (TSNAs), aldehydes, metals, volatile organic compounds (VOCs), phenolic compounds, polycyclic aromatic hydrocarbons (PAHs), flavorings, tobacco alkaloids, and drugs.   A range of other chemicals of concern were commonly detected, including benzaldehyde, trans-cinnamaldehyde and menthol. These chemicals are added for their almond, cinnamon and mint flavours, respectively. The presence of these chemical flavourings was concerning for a number of reasons.
Firstly, they’re all known to alter the effects of nicotine. Menthol makes nicotine more addictive.

Ingredient reactions.    Click HERE to read the full list of ingredients

E-liquid used in e-cigarettes have been found to be contaminated with fungi and bacteria. Beta-nornicotyrine are believed to be the result of bacterial action or oxidation during the extracting of nicotine from tobacco

Glycerol

Undiluted glycerol caused a variety of irritant-related effects, including petechial hemorrhage and erosions in the small intestine that were dose-dependent. When used as a drug, reported adverse effects following the oral administration of glycerol at unspecified doses included mild headache, dizziness, nausea, vomiting, thirst, and diarrhea.

Male Fertility:  One study found that glycerol injected into the testes of rats (50–200 µL and 862 mg/kg body weight) and monkeys (119 mg/kg body weight) suppressed spermatogenesis (CIR, 2015; Wiebe and Barr, 1984a,b; Wiebe et al., 1989).

Propylene Glycol

PG (also known as 1,2-dihydroxypropane, 1,2-propanediol, methyl glycol, and trimethyl glycol) is a clear, colorless, slightly syrupy liquid at room temperature. Some people have reported having an allergic reaction to PG. Some people have reported upper respiratory irritation after inhaling aerosolized PG for 1 minute (Wieslander et al., 2001), breathing aerosolized PG can also affect the risk of asthma development (Choi et al., 2010).

Trans-cinnamaldehyde

Severe effects on the immune cells in the lung.
 
Benzaldehyde

Benzaldehyde and trans-cinnamaldehyde are known to inhibit an enzyme called ‘CYP2A6’. CYP2A6 is responsible for metabolising and detoxifying many drugs humans are exposed to, including nicotine. Benzaldehyde is also a respiratory irritant and can reduce a person’s ability to fight off lung infections.