FIGURE 1.

Skin and mucosal barrier structure. The epithelial barrier of the skin and airways consists of four main components. (a): The epithelial layers—the epidermis consists of four sub‐layers and the airway epithelial barrier is made of a pseudostratified epithelium. (b): Structural proteins, such as filaggrin, natural moisturizing factor (NMF), ceramide, tight junctions (TJs), and adherence junctions (AJs). (c): Secreted molecules, such as mucin, anti‐microbial peptides, and fatty acids. (d) Microbiota on the surface of the epithelial barrier