Biophysical models for skin transport and absorption

Absorption of molecules (applied drugs and chemicals) through the skin proceeds by sequential diffusion steps through the stratum corneum (SC, barrier), viable epidermal, and dermal layers (1-3). Within each of these strata, absorption involves partitioning into and diffusion within several components of an inherently heterogeneous microstructure, and in the dermis it is accompanied by clearance into the systemic circulation via the dermal vasculature. Microscopic theoretical models of these transport processes have evolved to the point where they can often yield mechanistic understanding and reasonable quantitative predictions of transdermal transport rates, subsurface concentration levels, and rates of vascular clearance.