Comparative study of lung toxicity of E cigarette ingredients to investigate E cigarette or vaping product associated lung injury ScienceDirect 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 in e cigarettes might keep us healthy, says researchers What Is Monopropylene Glycol Used For? The Chemistry Blog What's in an e liquid or vape juice? The main ingredients are propylene glycol (PG) and vegetable glycerine (VG). These are solvents that are basically used to dissolve and carry the other ingredients. Electronic cigarette vapors from propylene glycol or glycerol alone Download Scientific Diagram