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J. Cosmet. Sci.J 55, 95-113 Qanuary/February 2004) Review of the current understanding of the effect of ultraviolet and visible radiation on hair structure and options for photoprotection VITTORIA SIGNORI, BASF Corporation, 1705 Route 46 West, Ledgewood, NJ 07852. Accepted for publication June 18, 2003. Synopsis This article describes the current understanding of the effect of ultraviolet (UV) radiation and visible light on the structure and integrity of human hair fibers furthermore, it discusses current and past approaches to the protection of hair from UV rays. Relevant literature is reviewed. INTRODUCTION Personal care products are formulated to deliver many benefits to the consumer. As the industry has become increasingly competitive, and the consumer has become more educated and at times rightfully skeptical of miracle-like claims printed on cosmetic products, the personal care scientific community has risen to the task of investigating the true cause of the effectiveness of some cosmetic treatments, and a great deal of under­ standing has been gained through these efforts. This knowledge is kept as a trade secret, patented, and delivered to the consumer in the form of innovative products, or shared openly in a scientific forum for the participating community to take part in the dis­ cussion. Either way, the whole personal care industry, some more enthusiastically than others, has embraced a more scrupulous way of looking at products and the scientific data in support of claims. In the hair care discussion, hair damage has long been recognized to be an issue of great concern to most consumers. Hair damage is a generally recognized term that encompasses a variety of attributes, among which are dryness, ease to breakage, split ends, a coarse feel, lack of manageability, and lack of luster. The following will give an overview of light and its interaction with organic compounds, solar simulators and their role in reproducing solar radiation, and the current under­ standing of the effect of ultraviolet (UV) radiation on the structure of human hair, as well as approaches aiming to limit these negative effects. 95