Endogenous skin and cytosolic proteins

Endogenous skin and cytosolic proteins refers to the collective group of proteins found within the layers of the skin and the internal environment of skin cells, such as keratinocytes and melanocytes. This term does not identify a single molecular target but rather a broad class of proteins—including keratins, serum albumin, and various cytosolic enzymes—that can interact with exogenous chemicals (OECD, 2023). In pharmacology and toxicology, these proteins are significant because they serve as carriers for haptens; small, reactive molecules that become immunogenic only after covalently binding to these endogenous proteins (NIH, 2022). This process, known as haptenization, is the critical first step in the development of allergic contact dermatitis and other delayed-type hypersensitivity reactions (Lepoittevin, 2006). Because this category encompasses thousands of distinct proteins with diverse biological roles, it is considered too non-specific to be a therapeutic target in the traditional sense. Instead, it is a focal point for assessing the skin sensitization potential of topically applied drugs and cosmetic ingredients.

Other names

Skin proteinsCytosolic proteinsDermal proteinsHapten-carrier proteins

Haptenization: The covalent binding of small reactive molecules (haptens) to nucleophilic sites on endogenous skin and cytosolic proteins to form a complete antigen capable of eliciting an immune response.