E liquid composition Vaping Post Toxicity and Appeal of Flavoured E Cigarettes and Flavour Ban Outcomes: A Narrative Review Researchers at the University of California, Riverside, found that heating propylene glycol, the main ingredient in most e cigarette liquids, can produce two toxic chemicals, methylglyoxal and acetaldehyde, which damage lung cells. Using Propylene Glycol an overview ScienceDirect Topics