Some of the most dangerous e cig flavors are cinnamon, vanilla, raspberry, pineapple, and orange. Besides flavors, e cigarette aerosol contains other dangerous chemicals like metals, formaldehyde 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, a component of electronic cigarette liquid, damages epithelial cells in human small airways Respiratory Research Springer Nature Link A Single Session of Vaping Can Hurt Your Lungs Liquid E Cigarettes Liquid nicotine used in e cigarettes still a danger to children despite recent decline in exposures