Ricinoleic acid (castor oil fatty acid) is a monounsaturated fatty acid that is the primary component of castor oil. It is named after the castor plant from which it is derived, Ricinus communis. Ricinoleic acid makes up about 85-95% of the fatty acids in castor oil. Ricinoleic acid has several notable characteristics, including its emollient and moisturizing properties, making it a common ingredient in cosmetic and personal care products such as creams, lotions, and lip balms. It also has anti-inflammatory and antimicrobial properties, which further enhance its usefulness in skincare formulations.

Ricinoleic acid can be used as emulsifier for chocolates and margarines (PGPR) and metal working fluids like soluble oils, semi synthetic fluids and fire resistant hydraulic fluids. Its unique chemical structure makes it useful in industrial applications. For instance, it can be converted into various derivatives such as sebacic acid, which is used in the production of nylon and other polymers. Additionally, it is a key component in the production of hydrogenated castor oil, which finds applications in cosmetics, pharmaceuticals, and other industries.