How are Non Combusted Cigarettes, Sometimes Called Heat Not Burn Products, Different from E Cigarettes and Cigarettes? FDA Les E Cigarettes 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