Flavorants and Propylene Glycol From e Cigarettes Form Harmful Irritants When Combined AJMC E cigarettes can emit formaldehyde at high levels under conditions that have been reported to be non averse to users Scientific Reports Understanding the Dangers of Vaping Prevention Poster Do Air Purifiers Help with Vape Smoke? Smart Air Propylene glycol, a component of electronic cigarette liquid, damages epithelial cells in human small airways Respiratory Research Springer Nature Link