ABSTRACT
INTRODUCTION Healthy mammalian skin provides a relatively efficient barrier to egress of endogenous compounds, particularly water, and the ingress of exogenous material. The outer layer of the skin (stratum corneum, the horny layer) is associated with the major barrier properties of the skin (1,2). One of the major physiological functions of the skin is the prevention of dehydration. The rate of water loss through skin to the surface, transepidermal water loss (TEWL), is a direct measure of the integrity of the stratum corneum barrier. Intact, normal skin of healthy subjects has a TEWL level of ~4 g/m2/hr. Many examples demonstrating a good correlation of elevated TEWL with increased penetration of topically applied compounds follow.
