Ricinus communis, also known as the castor oil plant, is a species of perennial flowering plant. The plant produces the castor bean, which, despite its name, is not a true bean but actually a seed. Pressing the seeds results in castor seed oil. The fatty acid chains present in castor seed oil are approximately 90% ricinoleic acid, with oleic and linoleic acid also being significant components. Castor seed oil is a colorless to very pale yellow liquid with a distinct taste and odor.

In cosmetics and personal care products, castor seed oil primarily functions as an emollient. Emollients work to soften and smooth the skin (or hair) while also acting as occlusive agents. Upon application, occlusive agents form a protective film on the surface of skin, which helps to prevent evaporation of the skin’s natural moisture. Over time, this increases skin hydration by causing buildup of water in the stratum corneum (the uppermost layer of skin). Due to these properties, castor seed oil can be found in creams, lotions, hair conditioners, and other types of moisturizers. Castor seed oil can also enhance the absorption of other cosmetic ingredients.