Nicotine Poisoning: What It Is, Symptoms, Causes & Treatment 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. Vaping harms your health Cancer Institute NSW What Does Vaping Do to Your Lungs? Johns Hopkins Medicine E cigarette, or Vaping Product, Use Associated Lung Injury (EVALI) Fact Sheets Yale Medicine