The skin forms a life-sustaining barrier between the organism and the physical environment. The physical barrier of the skin is mainly comprised of the stratum corneum (SC) and tight junctions (TJs). In recent years, there have been significant advances in our understanding of the epidermal TJ function, composition and regulation. In contrast to the SC, TJs are highly dynamic structures. It was discovered that spatiotemporal regulation of dynamic TJ replacement from cell to cell maintains the TJ barrier homeostasis of the skin, despite continuous cellular turnover. This review summarizes current knowledge about how TJ barrier homeostasis is maintained in simple and stratified epithelia, and how diseases and other conditions affect the TJ barrier in the skin.
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