Enzyme in cosmetic products can cause allergy
Papain is found naturally in papaya and is often referred to as a “plant-based pepsin” in reference to the digestive enzyme pepsin that is present in the stomach. Researchers looked at the effect of papain directly on the skin of mice as well as on skin cells in the petri dish. Skin consists of several layers joined via cellular connections called “tight junctions”. The project team showed that papain induces a breakdown of these cell-cell junctions. On the skin, papain results in a loss of the barrier function.
The cosmetic industry uses papain in exfoliating treatments to remove dead surface skin. There even are enzyme-based shampoos for house pets to clean the fur and make it easier to brush.
“After just a short period of time, papain increased vascular permeability and inflammatory cells infiltrated the skin,” Erika Jensen-Jarolim, Head of the Department of Comparative Medicine at the Messerli Research Institute, explains.
Around two weeks after being exposed to papain, the researchers found antibodies to papain in the mice. These immunoglobulins are the cause of the allergic reaction toward the enzyme.
“Exposed mice not only experienced a loss of the barrier function of the skin, but also had a specific allergic sensitization toward papain. The animals developed an allergy,” says allergy expert Jensen-Jarolim.
But the permeation of the skin barrier does not appear to be a prerequisite for sensitization toward papain.
“The enzyme remains allergenic even when its enzymatic function has been blocked,” explains Jensen-Jarolim.
The disruption to the skin barrier is essential for the infiltration of other allergens and bacteria. In humans and in animals, diseases of the skin such as atopic dermatitis, commonly referred to as eczema, involve an increased permeability of the skin with a heightened risk for bacterial, fungal, or viral colonisation. Besides genetic factors, allergenic enzymes from external sources may also contribute to the symptoms. It is striking that papain has an enormous structural similarity with one of the most important house dust mite allergens.
The authors conclude that sensitization toward these house dust mite allergens follows the same principle.
“People with sensitive skin as well as small children should avoid the enzyme (EC Number 18.104.22.168) as much as possible and observe the ingredients declaration for consumer products as regulated by EU Directive 2000/13/EC,” says Jensen-Jarolim.
Stremnitzer, C., Manzano-Szalai, K., Willensdorfer, A., Starkl, P., Pieper, M., König, P., Mildner, M., Tschachler, E., Reichart, U., & Jensen-Jarolim, E. (2015). Papain Degrades Tight Junction Proteins of Human Keratinocytes In Vitro and Sensitizes C57BL/6 Mice via the Skin Independent of its Enzymatic Activity or TLR4 Activation Journal of Investigative Dermatology DOI: 10.1038/jid.2015.58