Papain is an enzyme extracted from papaya. According to Natural Medicines Comprehensive Database, “Topically, papaya latex can cause severe irritation and blisters. Topical use of papain can cause itching. Severe allergic reactions have been reported in sensitive individuals.” Other research has confirmed that papain is a strong allergen on skin (in vitro and on mice). Papaya can be a skin irritant on par with hydrogen peroxide.
There’s one study showing it may be effective for exfoliation, but only in a pure concentration.
Research is extremely limited on papaya enzymes. Papaya enzymes and papain extract can result in serious skin irritation and allergic response, especially for anyone allergic to latex (papaya is a natural source of latex).
In skincare, papain is used in some toothpastes, shampoos, and facial creams. Most often, you’ll see it in enzyme exfoliants. Papaya has been used widely in folk medicine for many ailments: papaya juice for warts, corns, cancers, tumors, and thickened skin; papaya roots or their extracts for cancers of the uterus, syphilis, the tropical infection, hemorrhoids, etc.; and the latex for psoriasis, ringworm, or applied externally as an antiseptic or to heal burns or scalds.
While there is only limited data to support most of these uses, there is some evidence for healing bed sores and other wounds and in treating intestinal worms in humans. Papaya has antibacterial effects that could be useful in treating chronic skin ulcers to promote healing, however the study that claims this did not test its antibacterial effects on human or even animal skin.
Journal of Investigative Dermatology, February 2015, ePub
Indian Journal of Pharmacology, November-December 2012, pages 784-787
Archives of Dermatological Research, November 2001, pages 500–507 Antibacterial effects of Carica papaya fruit on common wound organisms.
Comparison of safety and efficacy of papaya dressing with hydrogen peroxide solution on wound bed preparation in patients with wound gape