E cigarettes aren't harmless, and combining them with cigarettes makes them even worse Study Summary Vaping Is Far From Harmless NOVA PBS Propylene Glycol E Liquid Flavour Concentrates UK Batterie cigarette electronique Propylene Glycol Detection in Saliva of Vape Users Using GCMS LCGC International What's in an e liquid or vape juice? The main ingredients are propylene glycol (PG) and vegetable glycerine (VG). These are solvents that are basically used to dissolve and carry the other ingredients.