Propylene glycol, a component of electronic cigarette liquid, damages epithelial cells in human small airways Respiratory Research Springer Nature Link VG PG Ratio Explained: Choosing the Right Vape Juice for Your Kit VSAVI E Liquids Vape Kits Frontiers Flavorless vs. Flavored Electronic Cigarette Generated Aerosol and E Liquid on the Growth of Common Oral Commensal Streptococci Vaping might be more dangerous than smoking New York Post On Health E cigarettes affect lung biology, even in those who've never smoked