An updated overview of e cigarette impact on human health Respiratory Research Springer Nature Link E cigarettes can emit formaldehyde at high levels under conditions that have been reported to be non averse to users Scientific Reports e Cigarettes Safety Not Yet Proven CANSA The Cancer Association of South Africa CANSA The Cancer Association of South Africa Propylene glycol, a component of electronic cigarette liquid, damages epithelial cells in human small airways Respiratory Research Springer Nature Link