Topographical variations in the skin barrier and their role in disease pathogenesis.

The skin barrier can be divided into at least four functional units: chemical, microbial, physical and immunological barriers. The chemical and microbial barriers have previously been shown to exhibit different characteristics in topographically distinct skin regions. There is increasing evidence that the physical and immunological barriers also show marked variability in different areas of the skin. Here, we review recent data on the topographical variations of skin barrier components, the contribution of these variations to the homeostatic function of the skin and their impact on the pathogenesis of specific immune-mediated skin diseases (such as atopic dermatitis and papulopustular rosacea). Recognition of these topographical barrier differences will improve our understanding of skin homeostasis and disease pathogenesis and provide a basis for body site-specific targeted therapies.