Vaping water: Is it a safe alternative to traditional e liquid? 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 Discover ePuffer Nicotine Free Vape Devices: Disposable E Cigarettes, E Cigars, and E Liquid Flavours in Canada Flavorants and Propylene Glycol From e Cigarettes Form Harmful Irritants When Combined Hawai'i Public Health Institute