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.