ABSTRACT
The stratum corneum is seen as the main physical barrier that prevents the entry
of solutes into the skin and manages the egress of water and endogenous
molecules from the body. It is the thin outermost layer of the skin consisting of
corneocytes (flattened, closely packed, and interdigitated “dead” cells packed with
keratin) embedded in a highly organized, dense lipid intercellular space (1,2). The
skin also has other barrier and support properties including immunological,
metabolic, cushioning, sensing, and temperature control. In addition, the blood
and lymphatics in the skin enable the removal of absorbed and skin metabolized
solutes into the systemic circulation for further detoxification and excretion.
The other distinct skin layers involved in providing these functions are the
viable epidermis, dermis, and hypodermis. In this chapter, we first review
the morphology of the viable skin layers and the skin appendages. We then
examine the role the substructures below the stratum corneum may play in the
physical and metabolic barrier properties of the skin and in the removal of solutes
absorbed into the skin.
