Thoroughly updated, this second edition is the most comprehensive reference on the methods available for the enhancement of percutaneous penetration. The book examines a broad scope of chemical enhancers and various physical methods of enhancement. The range of chemicals discussed is, arguably, unsurpassed anywhere in the literature. This edition contains comprehensive descriptions of the latest techniques and several chapters cover the modern analytical techniques adapted to assess and measure penetration enhancement. New to this volume are chapters addressing penetration retardation, important for substances such as sunscreen agents, for which skin penetration is not desirable.