A team at the University of North Carolina School of Medicine developed a system to quickly evaluate e - liquid toxicity.
The system uses large plastic plates which have hundreds of tiny indentations, in which the researchers place fast - growing human cells and expose them to different e - liquids. The more these liquids reduce the cells' growth rates, the greater their toxicity.
They found that even in small doses, two of the main ingredients of e - liquid - - propylene glycol and vegetable glycerin - - significantly reduced the growth of the cells.
As well as base ingredients, e - liquids also include small amounts of nicotine and flavoring compounds. However, after testing 148 e - liquids the team found the ingredients in each liquid varied greatly, and that on the whole, the more ingredients in the liquid the more toxic it was.
In particular, the flavor compounds vanillin and cinnamaldehyde showed the greatest toxicity effects, and are widely used in e - liquids. Co - first author Flori Sassano also added that, "The higher the concentrations of these compounds in particular, the more toxic the e - liquids were. "