What is Propylene Glycol (PG)?

Overview
Propylene glycol, also called propane-1,2-diol, is an organic compound with the chemical formula C3H8O2. It is a viscous colourless liquid which is nearly odourless but possesses a faintly sweet taste. Chemically it is classed as a diol and is miscible with a broad range of solvents, including water, acetone, and chloroform. It is produced on a large scale and is primarily used in the production of polymers but also sees use in food processing as the E-number E1520. The compound is sometimes called α-propylene glycol to distinguish it from the isomer propane-1,3-diol(β-propylene glycol).

Propylene Glycol (PG)

Propylene glycol is a clear, colorless, slightly syrupy liquid at room temperature. It may exist in air in the vapor form, although propylene glycol must be heated or briskly shaken to produce a vapor.
Propylene glycol is practically odorless and tasteless
Propylene glycol is a chemical made by reaction of propylene oxide with water
Propylene glycol has had an unsurpassed reputation for safe use in a wide range of consumer products, including food products, animal feed, cosmetics and pharmaceuticals, as well as industrial applications
It is used as a stabilizer (to keep things held together, and keep them from evaporating), and to keep foods moist. It is used in many of the foods that we eat, and the FDA deems it safe for human consumption Industrial grade propylene glycol is an ingredient used to make non-toxic antifreeze and deicing solutions for cars, airplanes, and boats; to make polyester compounds; and as solvent in the paint and plastics industries.

The point above needs a special note, since PG has been vilified in the media for being an ingredient in antifreeze. These reports fail to mention that they are referring to non-toxic antifreeze, giving consumers a false impression. This is a scare tactic used by the media, those who are misinformed and organizations against e-cigarettes.

Propylene glycol is the compound of choice for delivering atomized medications. It has been used in asthma inhalers and nebulizers since the 1950’s

In e-cigarettes, propylene glycol allows atomization to take place at substantially lower temperatures than required for a tobacco cigarette and will also help carry / deliver the nicotine when the vapor is inhaled
While the contents of the liquid solution found in cartridges may vary depending upon brands, the major ingredients usually remain the same.

Features of Propylene Glycol:

Serves as a solvent
Connects and stabilizes insoluble fluids (emulsifier)
Helps to bind and transport other substances (excipient)
Holds and dissolves active ingredients equally in a medium
Attracts/holds water/moisture (hygroscopic)
Reduces the freezing point
Increases the boiling point
Offers outstanding stability with high flash and boiling points

By emulsifying (mixing) active ingredients, which otherwise would not mix with one another, the propylene glycol creates a stable homogeneous fluid that will allow the intended final product, be it a face cream or shampoo, for example, to do its job.

Safety of Propylene Glycol

It has been used safely for more than 50 years, including in health-sensitive products such as food, cosmetics and pharmaceuticals, where the molecule mainly serves as non-active ingredient or carrier of other substances
Studies have proven that propylene glycol has a very low degree of toxicity
In the body, propylene glycol is rapidly converted into lactic acid, in a similar manner to what happens with sugar (energy) in the muscles during sports

Pharmaceutical Grade Propylene Glycol

Applications of propylene glycol:

To carry flavors in food and drinks
To make face creams, body lotions, deodorant-sticks, lipsticks and many other cosmetic articles soft, moist and consistent
To stabilize foams in cosmetic and healthcare products
To help pet and livestock feed retain its moisture and taste
To act as a carrier of active ingredients in vaccines, cough relief syrups or gel capsules to help deliver this substances within the body for treatment and prevention of diseases

Applications of propylene glycol in cosmetics and toiletries include products in:

Personal care: bath and shower soaps, gels, face cleansers, shaving foams, after shave, antiperspirant deodorants, roll-ons, sticks, lipsticks, fragrances, perfumes
Skin care: hand, body and facial moisturizers, sunscreen products
Hair care: shampoos, conditioners, styling gels
Oral care: mouthwashes, toothpaste
Baby care: wipes, antiseptics

Propylene glycol has been approved for use as a food additive. In direct food contact it is mainly used as:

Solvent and carrier of flavor or color in the food and beverage manufacturing processes, to make drinks, cookies, cakes, candy
Thickener, clarifier and stabilizer in food and beverage such as beer, salad dressings or baking products

Applications of propylene glycol as pet and cattle feed additive:

Humectant to provide moisture and taste. ” A humectant is a substance with the ability to attract and hold water in a formulation ”
Solvent, stabilizer and preservative to keep the feed suitable for longer use
Additive for increased energy provision

Some Pharmaceutical applications include: