Plant extract that is the source of the enzyme papain, which theoretically can have exfoliating properties on skin, although the majority of the research was not performed on skin. Papaya can be a skin sensitizer, but itŠ—Ès not as potentially risky as pure papain. Still, itŠ—Ès not an ingredient to apply daily; there are better options for leave-on exfoliants, including glycolic acid and salicylic acid.
References for this information:
Indian Journal of Pharmacology, November-December 2012, issue 6, pages 784-787