Comprehensive overview of common e-liquid ingredients and how they can be used to predict an e-liquid's flavour category

Abstract

Objectives: Flavours increase e-cigarette attractiveness and use and thereby exposure to potentially toxic ingredients. An overview of e-liquid ingredients is needed to select target ingredients for chemical analytical and toxicological research and for regulatory approaches aimed at reducing e-cigarette attractiveness. Using information from e-cigarette manufacturers, we aim to identify the flavouring ingredients most frequently added to e-liquids on the Dutch market. Additionally, we used flavouring compositions to automatically classify e-liquids into flavour categories, thereby generating an overview that can facilitate market surveillance.

Methods: We used a dataset containing 16 839 e-liquids that were manually classified into 16 flavour categories in our previous study. For the overall set and each flavour category, we identified flavourings present in more than 10% of the products and their median quantities. Next, quantitative and qualitative ingredient information was used to predict e-liquid flavour categories using a random forest algorithm.

Results: We identified 219 unique ingredients that were added to more than 100 e-liquids, of which 213 were flavourings. The mean number of flavourings per e-liquid was 10±15. The most frequently used flavourings were vanillin (present in 35% of all liquids), ethyl maltol (32%) and ethyl butyrate (28%). In addition, we identified 29 category-specific flavourings. Moreover, e-liquids' flavour categories were predicted with an overall accuracy of 70%.

Conclusions: Information from manufacturers can be used to identify frequently used and category-specific flavourings. Qualitative and quantitative ingredient information can be used to successfully predict an e-liquid's flavour category, serving as an example for regulators that have similar datasets available.

Keywords: electronic nicotine delivery devices; public policy; surveillance and monitoring; tobacco industry.

Figure 1

Mean number of ingredients indicated as having a ‘flavour and/or taste enhancer’ function (black) and ingredients with another function (grey) in total and for each of the separate flavour categories. Other functions of ingredients may include addictiveness enhancers, carriers, casings, fibres, humectants, solvents, processing aids, smoke odour modifiers, water-wetting agents and viscosity modifiers.