ABSTRACT
The skin is one of several epithelial systems positioned at an interface between internal organ sub-systems and the outside world. Uniquely, it has to combine multiple disparate functions into one organized system able to prevent excess water loss, limit percutaneous absorption, enable plasticity and elasticity, and provide protection against UV radiation. All these functions must also be integrated to provide a barrier against the natural tendency of microbes to establish and proliferate in the nutrient-rich environment established by the body. Microbes that are successful in exhibiting limited growth on the epithelial surface are defined as ‘‘nonpathogenic,’’ and those that invade and have the potential for unrestrained growth are defined as ‘‘pathogenic.’’ Ultimately, it is the immune barrier defense presented by the individual host that defines the pathogenic potential of any given microbe.
