Electronic cigarettes utilize a cartridge and an atomizer containing a small reservoir used to hold a liquid mixture. When the atomizer is heated, the liquid mixture is vaporized releasing the emulsified flavors and nicotine added to the mixture. The mixture used in electronic cigarettes to deliver nicotine and flavor is referred to as E-liquid or E-Juice. Propylene glycol (PG) and vegetable glycerin (VG), used as a base or carrier in E-liquids, also produces the vapor seen when the user exhales. Propylene glycol is used alone or in combination with vegetable glycerin, with each product exhibiting different characteristics. Both products are safe to use, with minor differences in flavor and burn quality reported by electronic cigarette users.
Due to its excellent stability and hemectant qualities, propylene glycol is used as a moisturizer in food, medicines, toothpaste and cosmetics. In addition to its use as a carrier in E-liquid, PG is also added to pipe tobacco to preserve moisture. Additionally, propylene glycol is used in products with flavorings due to its ability to compound citrus or other emulsified flavors often added to E-liquid.
According to Dow Chemical Company, manufacturer and distributor of propylene glycols, because of its low oral toxicity, propylene glycol is considered safe by the Food and Drug Administration (FDA) for use as a direct food additive and for use as a carrier in pharmaceuticals. With a shelf life of two years, stored below 104 degrees, propylene glycol should be kept in a closed container out of direct contact with ultraviolet light.
Some controversy surrounds propylene glycol due to its use in antifreeze. Consumers often come to an erroneous conclusion that if propylene glycol is used in antifreeze it is unsafe in food and cosmetic products. The typical ingredient found in antifreeze, ethylene glycol, is highly toxic and is responsible for hundreds of animal deaths each year due to accidental ingestion. Because of these concerns and potential risk to humans, propylene glycol is sometimes used in place of ethylene glycol because its low toxicity.
Ethylene glycol and propylene glycol. when added to antifreeze, act as a carrier for the product to prevent the mixture from freezing. Proponents for the use of propylene glycol in antifreeze include The American Society for the Prevention of Cruelty to Animals. The fact that two products have a common ingredient, doesn’t imply the products are identical. PG is also used in moisturizers and toothpaste which can be toxic when ingested, due to other non-food grade ingredients or toxic chemicals, such as fluoride in toothpaste. More education about the safety of propylene glycol is needed to allay fears of consumers.
Vegetable glycerin, or vegetable glycerol, is a plant-based carbohydrate used as a base, moisturizer or carrier in common food and health products such as cake mix, toothpaste, and gel capsules. When used in E-liquid, vegetable glycerin produces vapor that mimics the appearance of smoke as it is exhaled. Vegetable glycerin is sometimes preferred over propylene glycol because of its increased vapor production. Vegetable glycerin is thicker than propylene glycol, which may reduce the life of the e-cigarettes atomizer when used at full strength. Combining propylene glycol and vegetable glycerin in mixtures of at least 80 percent PG and 20 percent VG may eliminate extra wear and tear on the atomizer without compromising the quality of vapor.
The safety of vegetable glycerin is virtually undisputed. According to studies in the United States and Canada, VG is hypo-allergenic and non-carcinogenic. VG has low potential to irritate eyes or other mucus membranes and is not known to cause skin reactions. When skin irritation does occur, it is usually due to skin coming into contact with high concentrations of vegetable glycerin not used in E-liquid products. VG is metabolized easily by the body and produces very low toxicity when inhaled or ingested.
One of the common side effects reported from use of VG in E-liquid, is mild sore throat and dry mouth. Increasing water intake usually alleviates side effects. Users have commented that mild side effects usually subside on their own after a few days of use. This resolution is usually due to the body’s ability to quickly adjust to vegetable glycerin in the body’s system.
While vegetable glycerin is a carbohydrate derived from plant oils, and propylene glycol is an organic compound produced in the laboratory using organic and natural materials, both are considered safe for ingesting or inhaling. Ultimately, whether to use a PG or VG-based E-liquid comes down to individual user preference. Both bases provide an adequate and enjoyable delivery system, without major differences in taste and vapor production.