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 All E Cigarettes Emit Harmful Chemicals, but Some Emit More Than Others Berkeley Lab Berkeley Lab News Center 1,2 Propylene Glycol: A Biomarker of Exposure Specific to e Cigarette Consumption An updated overview of e cigarette impact on human health Respiratory Research Springer Nature Link Top 10 E liquide menthe The Impact of E Cigarettes on the Lung Providers AmeriHealth Caritas Pennsylvania