Hi Beccca! This is part of something I wrote on the topic:
...the nicotine in U.S. made e-liquids is the same pharmaceutical nicotine found in products such as the patch and gum; propylene glycol is often used (among other things) as an ingredient in drops to treat dry eye symptoms and as a solvent for drugs insoluble in water enabling them to be injectable; the flavorings used are food grade; and vegetable glycerin is used as an enema. Candidly, if substances can be put in your eyes, injected into your body, swallowed or pumped up your rectum, how harmful can they be to inhale? Compared to the known carcinogens in cigarette smoke, I’m not worried about it.
Also VG is used in the health food industry to extract the healing qualities of herbs and spices.