E-cigarette Flavorings May Become Toxic, Trigger Inflammation

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Sweet, fruity flavors added to electronic cigarettes (e-cigarettes) react with vaping liquid to create new compounds that could trigger irritation and inflammation when inhaled. Chemical flavorings in e-cigarettes for vanilla, cherry, citrus, and cinnamon mingle with solvents, such as polypropylene glycol and glycerol, creating potentially toxic compounds that endure.

“These individual ingredients are combining to form more complex chemicals that are not disclosed to the user,” said senior author Sven-Eric Jordt, PhD, associate professor of anesthesiology, pharmacology and cancer biology at Duke University. “When inhaled, these compounds will persist in the body for some time, activating irritant pathways. Over time, this mild irritation could cause an inflammatory response.”

The researchers published their results on October 18, 2018 in Nicotine & Tobacco Research.

“Vaping” e-cigarettes has become increasingly popular with youth, driven by the wide range of available flavors, often created using flavor aldehydes. “In some countries, there’s a consensus that e-cigarettes might help chronic smokers quit traditional cigarettes,” said Jordt. “However, in the US we are seeing increasing numbers of adolescents using them. Adolescents with developing lungs are more prone to irritation, allergies and asthma. It’s important for families and kids to know about the potential dangers.”

“Adolescents with developing lungs are more prone to irritation, allergies and asthma. It’s important for families and kids to know about the potential dangers.”

Jordt and colleagues used gas chromatography to determine concentrations of flavor aldehydes and reaction products in e-liquids and vapor generated from a commercial e-cigarette. Flavor aldehydes, including benzaldehyde, cinnamaldehyde, citral, ethylvanillin, and vanillin, rapidly reacted with the e-liquid solvent propylene glycol after mixing. Upward of 40% of flavor aldehyde content was converted to flavor aldehyde propylene glycol acetals, which were also detected in commercial e-liquids.

Acetals carry over to e-cigarette vapor

Acetal carryover rates 50% to 80% 

Vaping experiments showed carryover rates of 50%–80% of acetals to e-cigarette vapor. Acetals remained stable in physiologic aqueous solution, with half-lives of more than 36 hours, suggesting they persist when inhaled by the user, the researchers stated.

Some research on e-cigarettes suggests that higher vaping temperatures increase the risk that vapors will contain potentially harmful chemicals including formaldehyde, a suspected carcinogen. Vaping advocates suggest low-temperature or temperature-adjustable vaporizers minimize those risks. The new study shows chemical changes occur even before the liquids are heated, so users may face some risks when inhaling the aerosolized ingredients at any temperature.

The new study shows chemical changes occur even before the liquids are heated, so users may face some risks when inhaling the aerosolized ingredients at any temperature.

Vaping liquids contain between 0.5% to 10% flavor additives, depending on the desired intensity, the researchers said. For this study, they analyzed liquids with 0.8% to 2.5% flavor additives.

Flavor aldehydes are known to cause irritation when inhaled. The researchers found the acetals they created from mixing flavors into e-liquids were even more effective in triggering molecular receptors involved in lung irritation, the same receptors that maintain irritation and inflammation in people with asthma or those who have inhaled smoke or fumes.

“Individuals who use e-cigarettes frequently should know they are exposing themselves to these chemicals, and that the long-term effects of these chemicals on the airways are unknown,” said coauthor Hanno Erythropel, PhD, a postdoctoral associate in chemical and environmental engineering at Yale University.

The researchers advise a rigorous process to monitor the potentially changing composition of e-liquids and e-vapors over time to identify possible health hazards.