The cosmetic industry commonly uses the enzyme papain in exfoliating products that remove dead surface skin, such as Ole Henriksen Blue Black Berry Enzyme Mask and Elemis Papaya Enzyme Peel. The papaya-derived enzyme degrades proteins and is used extensively in the food and cosmetics industries.
Scientists at the University of Vienna Medical School and the University of Veterinary Medicine Vienna (Stremnitzeret al., 2015) have published a study in the Journal of Investigative Dermatology showing that that humans and animals can have strong allergic skin reactions when they come in contact with the enzyme. In the lab, the study showed that this may be because tight junction proteins, which join human skin cell layers together are degraded by the enzyme.
As a result, the skin becomes more permeable, barrier function of the skin is lost, and bacteria and inflammatory cells infiltrate the skin, causing an allergic reaction and the release of antibodies to papain. The authors of the research article note that papain has a very similar structure to a common house dust mite allergen.
Researcher Erika Jensen-Jarolim, Head of the Department of Comparative Medicine at the Messerli Research Institute notes that "people with sensitive skin as well as small children should avoid the enzyme (EC Number 126.96.36.199) as much as possible and observe the ingredients declaration for consumer products as regulated by EU Directive 2000/13/EC."