The second edition of this thorough reference is an invaluable tool for assessing cosmetic products, addressing both the quality of the product and the effect it has on the skin. Since a product's ultimate purpose is to benefit the skin, it is crucial to have an understanding of how the skin works, how and why a product may or may not penetrate it, and what care individual skin types and conditions may require. It is difficult to discuss product ingredients without correlating product performance to skin function. An expanded section on skin physiology and chemical concepts enables the reader to better understand product performance through a thorough explanation of how chemicals and ingredients interact. The various skin types, conditions, and appropriate ingredients for treatments provide a quick reference to address clients' needs. This enlarged second edition contains over 2,000 ingredients including 200 new and updated entries. Expanded information on antioxidants and their stability, new discussion on aging and sensitive skin, and function of SPF and new sunblock ingredients offering full spectrum sunscreen and sunblock for both UVA and UVB rays has been added.