Researchers examined the flavor components of e-cigarettes to determine if they are potentially reactive.
E-cigarettes, or “e-liquids”, have increased in popularity in recent years due to their variety of flavors and their use for “vaping” among youth. E-cigarette flavors (vanilla, cherry, among others) are made from fragrant aldehydes. These aldehydes mix with nicotine, propylene glycol (PG) and glycerol (VG) to make the typical e-liquids.
PG and VG are made of chemical alcohol components. Chemical alcohols and aldehydes can react to produce acetals. The formation of aldehyde PG acetals may be possible with aldehyde flavors and alcohol constituents from e-liquids.
Can e-cigarette flavors become irritant and toxic?
There is an ongoing debate on whether or not these chemical products, or even just the initial flavor chemical, are possible irritants or toxic species. Some other aldehyde species have been shown to be irritants. Erythropel and colleagues recently set out to see if an actual reaction does occur between the aldehyde flavors and PG. They specifically wanted to see if e-cigarette flavors are potentially toxic. This study was published in the journal Nicotine & Tobacco Research.
E-cigarette flavors may not be completely stable
The researchers performed their experiments of the chemical mixtures (e-cigarette flavors and PG or PG/VG mix) in vials. They then analyzed them using a gas chromatograph. A chromatograph is capable of recognizing aldehydes and PG acetals.
For experiments with the commercial e-liquids, they purchased the e-liquids and also ran them through the gas chromatograph to see aldehyde, aldehyde PG acetals and in this case, nicotine as well. In addition, e-vapor could also be analyzed with a gas chromatograph.
The vials of e-cigarette flavors showed no significant changes in composition over time. However, they did notice some formation of PG acetals in some flavors. Overall, it seems that the ratio of PG/VG and the type of e-cigarette flavors affect how quickly PG acetals form.
They observed a similar trend with the commercial e-liquid. They showed in tests – seeing if this composition containing the PG acetals would carry over into the respiratory airway – that much of it does seem to carry over into the airways, even in vapor form (about 50-80%).
They also showed that these e-cigarette flavors have products that do not completely decompose into harmless products in the airway surfaces and may need to be examined for further toxicological or biological effects.
Finally, the authors used cell models to determine if the e-cigarette flavors were able to respond to certain irritant receptors that can be found in human respiratory pathways. They found that PG acetals did activate the pathway, and in some cases, had a stronger response than other irritant aldehydes.
E-cigarette flavors are reactants and likely irritants
The authors showed that e-cigarette flavors are reactive and likely irritants. There is a need for more testing and more safety regulations. The regulations need to ensure that the labeling, storage, and consumer information on e-cigarettes and vapors are accurately in line with current findings.
The authors suggest that more scrutiny on the whole life cycle of the product may be needed, as chemical composition may vary from the initial production phase up to ingestion or inhalation in humans.
Written by Olajumoke Marissa Ologundudu B.Sc. (Hons)
Reference: Erythropel HC, etal. Formation of flavorant–propylene Glycol Adducts With Novel Toxicological Properties in Chemically Unstable E-Cigarette Liquids. Nicotine Tob Res.2018; 1-11. doi:10.1093/ntr/nty192.