Propylene glycol (PG) is a colorless and odorless liquid chemical used for decades in a wide array of applications. A synthetic substance produced in industrial quantities, it is a relatively simple organic compound that has the chemical formula C3H8O2. The U.S. Food and Drug Administration considers PG as non-toxic in small amounts; however, large doses can cause seizures in humans and kidney and liver damage in animals.

In foods, PG absorbs water and maintains moisture. It dissolves food dyes and flavorings in drinks, and it keeps foods from freezing, such as in breweries and dairies. In food, it would be difficult to consume a dangerous dose, but babies, infants, the elderly and those with certain allergies may be more sensitive to the chemical.

In cosmetics, PG is commonly used to emulsify oil components to water-based components. Propylene glycol also helps cosmetic items keep from melting in high heat and freezing in low temperatures. The small amounts used in cosmetics do not pose health risks, except to those with sensitivities.

In medicines, PG acts as an emulsifier, specifically in topical agents and injectable medicines. It also acts as an excipient, or solvent, for the active ingredients in medications. Newborns have shown adverse reactions to medicines using this chemical.

Propylene glycol has a myriad of functions in industrial applications. The textile industry uses it as an intermediary in the production of polyester fiber. The military uses it to form smoke screens for troops. Military and commercial airlines use it as a de-icer for planes, however, ethylene glycol is also used because of its lower cost. PG can be found in liquid detergents, as well as a number of other uses.