ABSTRACT
When confronted with an organ as complex as skin, a biologist tends to want to relate structure to function at the most fundamental level, and indeed an enormous amount of complexity may be found. A physical scientist, on the other hand, looks for simplifying assumptions that allow him to describe the system within a mathematical framework and to make quantifiable predictions about its behavior. There is often a credibility gap between the two approaches, and the appropriate balance point moves as different problems are addressed. There is little doubt that the elegant work of Elias (1,2), Steinert (3,4), Wertz (5,6) and many others in the chemistry and structural biology of the stratum corneum (SC) has enormously increased our understanding of skin barrier function; however, the simplifying framework introduced by Scheuplein and Blank (7) and advanced by others, including Flynn (8), Roberts (9,10), Cooper (11), and Potts and Guy (12), has had a comparable impact on quantifying its properties. The Potts-Guy model for steady-state skin permeability (12) and extensions thereof (13) are arguably the most widely used predictive tools in transdermal drug delivery and dermal risk assessment (14).
