Vegetable oil derived from the castor bean whose main fatty acis is ricinoleic acid. It is used in cosmetics as an emollient, though its unique property is that when dry it forms a solid film that can have water-binding properties.
Castor oil can also enhance the absorption of other cosmetic ingredients. It is rarely associated with skin sensitivity, but can have a slightly sticky feel on skin.
Castor oil may also show up on an ingredient label by its Latin name, Ricinus communis.
Despite what you may have heard or read online, there is no substantiated research to prove that castor oil can stimulate hair growth.
Reference for this information:
Green and Sustainable Chemistry, November 2015, pages 154-163
International Journal of Toxicology, 2007, pages 31-77