title: Percutaneous absorption.
abstract: Clinical effectiveness of topically applied medications depends on the ability of the active ingredient to leave its vehicle and penetrate into the epidermis. The stratum corneum is that layer of the epidermis which functionally is the most important in limiting percutaneous absorption, showing the characteristics of a composite semipermeable membrane. A mathematical expression of transepidermal diffusion may be derived from Fick's Law of mass transport; factors altering the rate of diffusion are discussed.
mesh_terms: D000287:Administration, Topical; D001692:Biological Transport; D002463:Cell Membrane Permeability; D003681:Dehydration / Q000378:metabolism; D004058:Diffusion; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D006801:Humans; D008433:Mathematics; D004364:Pharmaceutical Preparations / Q000008:administration & dosage / Q000378:metabolism*; D014677:Pharmaceutical Vehicles; D012867:Skin / Q000187:drug effects; D012869:Skin Absorption; D012871:Skin Diseases / Q000378:metabolism; D012881:Skin Temperature; D012995:Solubility; D012997:Solvents; D013501:Surface-Active Agents / Q000494:pharmacology; D014783:Viscosity; D014867:Water / Q000378:metabolism
chemical_list: D004364:Pharmaceutical Preparations; D014677:Pharmaceutical Vehicles; D012997:Solvents; D013501:Surface-Active Agents; D014867:Water; D004121:Dimethyl Sulfoxide