The longest use of propionic acid historically has been as a preservative. Propionic acid is naturally antimicrobial and inhibits the growth of mold and some bacteria at low concentrations. It’s used both in animal feed and in many processed foods for human consumption, like cheese and bread. Due to its antimicrobial properties and low toxicity, propionic acid is also often used to sanitize surfaces where grain is to be stored. Different forms of the acid are used for different purposes- for example, sodium or calcium salts of propionic acid are typically used in human food, while the ammonium salt or direct acid is used in animal feed.

Propionic acid is used in herbicides and fungicides due to those same antimicrobial properties. It has also been found to be an effective bee repellant, useful for beekeepers who need to harvest honey from their colonies. It’s also used as a chemical intermediate in the manufacture of plastics, cosmetics, textiles, and various other products.