Study: E-liquid flavors may produce harmful chemicals when heated

An Irish study suggests that a new wave of chronic diseases could emerge in the next 15 to 20 years as a result of long-term exposure to toxic chemicals produced by pyrolysis of e-cigarette flavourings. The team from the Department of Chemistry at the Royal College of Surgeons Ireland (RCSI) are warning of the potential dangers of the “cocktail of chemicals” produced by heating the wide range of flavourings currently available.

Vaping devices heat e-liquids to high temperatures (100° to 400°) allowing the formation of an aerosol that is inhaled by the user. These liquids contain vegetable glycerin, propylene glycol, nicotine and flavorings, mixed in different concentrations.

The study, published in Scientific Reports[1], notes that the potential health risks are partly unpredictable given the wide variety of devices and their rapid evolution, as well as the range of flavors offered and the unlimited possibility of mixing these numerous products in varying concentrations.

Dangerous and toxic chemicals

The research used artificial intelligence (AI) to simulate and characterize the formation of new chemical compounds resulting from the pyrolysis by heating of e-liquid flavors.

The study analyzed 180 different chemicals contained in e-liquids. These chemicals are mainly derived from the food industry, and therefore intended to be ingested, not inhaled. By heating them, a single chemical can be the origin of 10 to 20 distinct compounds through pyrolysis, and these new products can themselves also be subjected to this pyrolysis and be the origin of new products. Finally, all these new products can potentially react with each other.

Almost all flavors submitted to the AI model produce at least one product classified as hazardous to health, and some several, the presence or absence of nicotine in the e-liquids not being a factor.

The formation of hazardous chemicals, including 127 classified as acutely toxic, 153 as hazardous to health and 225 as irritants, was observed, including, for example, volatile organic compounds (VOCs) following the pyrolysis of fruity and sweet flavours, thus confirming previous observations.[2] which demonstrated the production of these VOCs which are toxic to health.

Authors call for banning flavors in vaping products

Given the popularity of flavorings among adolescents and young adults, both smokers and non-smokers, it is essential to consider and prevent the potential long-term effects of regular inhalation of these products, in terms of morbidity and mortality, the study concludes. As such, AI can be an asset in providing informed advice to the general public, policy makers and health professionals.

According to senior author Donal O'Shea, professor of chemistry at RCSI, these results show that there is a need to ban all flavourings in vaping products. "before it's too late", because "It is plausible that we are on the cusp of a new wave of chronic diseases that will emerge in 15 or 20 years because of these exposures."

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[1] Kishimoto, A., Wu, D. & O'Shea, DF Forecasting vaping health risks through neural network model prediction of flavor pyrolysis reactions. Sci Rep 14, 9591 (2024). https://doi.org/10.1038/s41598-024-59619-x

[2] Chen, J.Y., Canchola, A. & Lin, Y.-H. Carbonyl composition and electrophilicity in vaping emissions of flavored and unflavored e-liquids. Toxics 9, 345 (2021).