ABSTRACT
INTRODUCTION The skin’s vital role as a protective barrier is often considered the most important of its many functions. Skin protects against mechanical injury, UV radiation damage, microbial infection, and permeation of harmful chemicals. In addition to protecting the body from these environmental insults, the skin also prevents rapid dehydration by slowing down the evaporative loss of internal water (see Chapter 7). Although the skin has many different protective barrier functions, it is the skin’s ability to limit the movement of molecules, including water, from both inside-tooutside and from outside-to-inside, that is perhaps most commonly associated with the word “barrier.” Amazingly, this permeability barrier function is localized almost entirely in the skin’s outmost layer, the paper-thin stratum corneum (SC), a highly organized assembly of lipid-depleted corneocytes embedded in a lipid-enriched extracellular matrix (1-4).
