Cytotoxic and oxidative effects of commercially available propylene glycol (PG) and vegetable glycerin (VG): Common humectants in electronic cigarettes ScienceDirect Vaping is the act of inhaling a heated, aerosolized substance. It is critical to distinguish vaping from smoking. Smoking is the inhalation of a burned substance. The main difference between the two Propylene Glycol in E Cigarettes Is PG Dangerous to Inhale? E Cigarette Direct Vaping and e cigarette use is a troubling trend Fort Plain Central School District Predicting the pulmonary effects of long term e cigarette use: are the clouds clearing? European Respiratory Society