part 1 INTRODUCTION -- chapter 1 Penetration Enhancer Classification / chapter 2 Structure–Activity Relationship of Chemical Penetration Enhancers / chapter 3 Quantitative Structure–Enhancement Relationship and the Microenvironment of the Enhancer Site of Action / chapter 4 The Role of Prodrugs in Penetration Enhancement / part 2 VEHICLE EFFECTS IN PENETRATION ENHANCEMENT -- chapter 5 Penetration Enhancement by Skin Hydration / chapter 6 Enhancement of Delivery with Transdermal Sprays / chapter 7 Hydrogel Vehicles for Hydrophilic Compounds / chapter 8 Enhanced Skin Permeation Using Ethosomes / chapter 9 Microemulsions in Topical Drug Delivery / chapter 10 Nanoparticles as Carriers for Enhanced Skin Penetration / chapter 11 Solid Lipid Nanoparticles for Topical Delivery / chapter 12 Fatty Alcohols and Fatty Acids / chapter 13 Essential Oils and Terpenes / part 3 PHYSICAL METHODS OF PENETRATION ENHANCEMENT -- chapter 14 Iontophoresis: Clinical Applications and Future Challenges / chapter 15 Electroporation / chapter 16 Microneedles / chapter 17 Vesicles under Voltage / part 4 ASSESSMENT OF PENETRATION ENHANCEMENT -- chapter 18 Mechanistic Studies of Permeation Enhancers / chapter 19 Penetration Enhancer Assessment by Corneoxenometry / chapter 20 Assessment of Vehicle Effects by Skin Stripping / chapter 21 The Use of Skin Alternatives for Testing Percutaneous Penetration / chapter 22 High Throughput Screening of Transdermal Penetration Enhancers: Opportunities, Methods, and Applications / chapter 23 Confocal Laser Scanning Microscopy: An Excellent Tool for Tracking Compounds in the Skin / part 5 THE RETARDATION OF PERCUTANEOUS PENETRATION -- chapter 24 Fundamentals of Retarding Penetration / chapter 25 Retardation Strategies for Sunscreen Agents / chapter 26 Military Perspectives in Chemical Penetration Retardation / chapter 27 Preclinical and Clinical Development of a Penetration Enhancer SEPA 0009