Conventional and multi omics assessments of subacute inhalation toxicity due to propylene glycol and vegetable glycerin aerosol produced by electronic cigarettes ScienceDirect Toxicity and Appeal of Flavoured E Cigarettes and Flavour Ban Outcomes: A Narrative Review E liquid composition Vaping Post 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 Vaping safe. Know what's inside. Protect their future. TalkNowAZ.com