By the term ‘barrier organ’ we mean the set of epithelia in the body, on whose integrity our survival depends. Numerous components contribute to the constitution of the barrier. In fact, there is a chemical, immunological, micro-biological and a physical barrier. The latter, at skin level, is much more complex than in other epithelia and is regulated by a well-defined set of molecules involved in the metabolism of filaggrin, the formation of the stratum corneum, the synthesis of intercellular lipid lamellae, the organisation of corneodesmosomes, desquamation and the formation of tight junctions (TJs), which reduce the intercellular spaces between epithelial cells until they disappear. In particular, it is the stratum corneum and the TJs, which are present in it, especially in the compact layer, that are responsible for permeability, which in other epithelia is provided by the TJ system. In addition, recent investigations have shown that partial or total inhibition of TJ proteins modifies epithelial permeability by interfering in the metabolism of filaggrin and lipids with abnormal formation of the stratum corneum.
