"Over the last half century, and especially over the last 15 years, understanding of the structure and function of the stratum corneum has evolved tremendously. Once conceptualized as an inactive film formed by lifeless, disintegrating keratinocytes, the stratum cor- neum is now recognized as a viable, functional structure that plays an important role in maintaining skin health and possibly mediating cutaneous diseases. Researchers and clinicians have also come to realize that the barrier functions not only to prevent the entry of exogenous factors, such as irritants or allergens, but that it also can mediate disease. We had already realized that dysfunction of the barrier may itself directly contribute to the pathogenesis of skin diseases, notably atopic dermatitis. More specifically, evidence shows that epidermal barrier dysfunction is likely to be a precursor of cutaneous inflammation."