ABSTRACT
INTRODUCTION Prevention of desiccation of the body is a major function of the skin. This function is performed for the most part by skin’s epidermis, with a particularly crucial contribution by the outermost layers, the stratum corneum (SC). At the skin’s surface there is a delicate balance between the water content of the SC and the environment, and although the SC contains relatively little water, a critical level of moisturization is essential for the normal barrier function and health of the skin. To maintain the proper level of moisturization, the skin’s epidermis has evolved a ‘nely tuned differentiation program which generates and maintains an SC composed of cellular and macromolecular components that provide the required structure, humectancy, and barrier to water loss (1). The SC consists of three basic components: corneocytes (terminally differentiated keratinocytes), corneodesmosomes (proteinaceous rivets holding corneocytes together), and lipids. A widely employed, if oversimpli‘ed analogy of SC structural organization is a brick wall (2,3). This analogy provides an image of a heterogeneous structure of two major components: bricks and mortar (Figure 14.1). In this model, the corneocyte ‘bricks’ occupy most of the volume of the SC wall and are surrounded by a lipid “mortar.” It is now recognized that the corneodesmosomes are a vital element of the mortar, ensuring structural integrity. Equally, the size and shape of the corneocytes inuence skin barrier function as well as the total thickness of the SC. One must also not forget the role of ‘laggrin and its degraded components in SC functioning (1).
