Propylene glycol (PG)
Propylene glycol is commonly used in asthma inhalers and so-called “fog-machines” which you can find in most nightclubs and other entertainment venues. Propylene glycol is “recognized as generally safe” by the US Food and Drug Administration (FDA). It is also used as a preservative in some foods and as a solvent in various pharmaceuticals.
Vegetable glycerin (VG)
Vegetable glycerin is a completely non-toxic substance, as it is widely used as a solvent, sweetener and preservative in the food industry. You can find this substance in soap, beauty products, baked goods, candy, pasta, soups, sauces, eye drops, toothpastes and pet food. It is considered “extremely neutral” when inhaled.
Aside from PG and VG, the only other substances found in electronic cigarette vapor are flavorings. The majority of e-liquid manufacturers use food grade flavorings, which are mostly considered safe when inhaled. Although not all of these flavorings are proven to be safe for inhalation yet, e-cigarette e-liquid, when vaporized, contains a very tiny and nonessential amount of these substances.
If your e-liquid contains it, you, of course, also inhale nicotine, which, without doubt, is a harmful and very addictive alkoloid. However, e-liquids without any nicotine content are widely sold all over the world, and are quite popular in the midst of many vapers.