By the grace of peeling: The brace function of the stratum corneum in the protection from photo-induced keratinocyte carcinogenesis

Chemical peeling with salicylic acid in polyethylene glycol vehicle (SA-PEG) is a safe and effective method for the rejuvenation of photo-damaged skin. The procedure removes photo-damaged stratum corneum, which consists of immature, fragile cornified envelopes (CEs) and stimulates the reconstruction of the stratum corneum with mature, rigid CEs. In UVB-irradiated hairless mice this procedure, which affects the stratum corneum only, suppresses skin tumor development. In addition, chemical peeling with SA-PAG suppresses p53 expression in mice and normalizes keratinocyte differentiation in both mice and humans. The stratum corneum functions as a barrier against physical and chemical insult and various infectious agents. Here, we hypothesize on a new function of the stratum corneum: a brace function that structurally protects keratinocytes from atypical differentiation or disordered proliferation. Although the precise mechanism remains to be elucidated, there is definite value to be gained from further investigation. This review discusses basic information about chemical peeling with SA-PEG, looks at its action on photo-induced tumor suppression, and proposes a new function for the stratum corneum in keratinocyte proliferation/differentiation.