Do you know what you're vaping? Propylene glycol (PG) and vegetable glycerin (VG) are the main liquids in vapes. When heated, these chemicals turn toxic and aren't safe to breathe. E cigarettes can emit formaldehyde at high levels under conditions that have been reported to be non averse to users Scientific Reports Tout savoir sur le propylne glycol dans les cigarettes lectroniques Formaldehyde Hemiacetal Sampling, Recovery, and Quantification from Electronic Cigarette Aerosols Scientific Reports