Vapes on black market may contain toxic chemicals, pesticides, harmful flavorings Harmful Chemicals in Vapes and E Liquids You Should Avoid SMOKO E Cigarettes 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. Vape juice contains a long list of chemicals, many of which aren't even listed on the packaging. Testing has also shown that vapes labelled "nicotine free" can have high nicotine levels.