ii scientific literature and regular speakers at conferences and technical symposia. We wish to sincerely thank all our contributors for the time and effort involved in preparing the chapters herein. Putting together this book has been an enjoyable, albeit sometimes stressful, experience and we express thanks to Brian W. Budzynski and Angela Kozlowski of Alluredbooks for guiding us through the process. Trefor Evans would like to acknowledge the underlying contribution associated with so many enjoyable working relationships with friends and colleagues across the industry over the past 20 years. In addition, and most importantly, he expresses his thanks and love to Terri Gordon for all her support and inspiration. Randy Wickett would like acknowledge and thank Professor J. Leon Lichtin, founder of the Cosmetic Science Program at the University of Cincinnati. Without Dr. Lichtin he would not be teaching cosmetic science today and this project would not have happened. He would also like to thank the many graduate students he has mentored over his more than 20 years at UC for their hard work and dedication to cosmetic science. He gives special thanks to Robin Wickett, his wife of more than 44 years, for her love and support through all his endeavors including the preparation of this text. Trefor Evans and R. Randall Wickett