Book excerpt: Milady's Skin Care and Cosmetic Ingredients Dictionary, third edition, is a multi-purpose resource for cosmetic professionals and consumers alike. Part one puts cosmetics in the context of skin care. It provides an overview of skin physiology. In order to understand how and why a product works it is essential to understand how the skin works. It gives an overview of the complexity of cosmetic chemistry particularly with respect to product penetration, and highlights the current challenges facing cosmetic formulators. In addition, it offers comprehensive discussion of the various skin types and conditions in order to help professionals in their product selection. Lastly, it defines common cosmetic industry terminology used by cosmetic manufacturers, professional estheticians, marketers and the media. The second part is dedicated to helping cosmetic users identify the function and purpose of specific ingredients. It is an alphabetical dictionary that lists and describes not only active principles but all other categories of ingredients that comprise a skin care cosmetic. As scientific knowledge of skin physiology and cosmetic chemistry advances, so do cosmetic products. This volume puts everything in context in an easy to read, easy to understand, user-friendly format.