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j. Cosmet. Sci., 54, 271-281 (May/June 2003) UV radiation: Aggressive agent to the hair--AFM, a new methodology of evaluation V. F. MONTEIRO, A. S. PINHEIRO, E.R. LEITE, J. A.M. AGNELLI, M. A. PEREIRA-DA-SILVA, and E. LONGO, CMDMC/LIEC/DQ/UFSCar (V.F.M., A.S.P., E.L.) and DEMa/UFSCar •.A.M.A.), Universidade Federal de S•7o Carlos, Rod Washington Luis Km 235, Caixa Postal, 676, S•7o Carlos, SP, Brazil 13565-905 and Universidade de S•7o Paulo, Instimto de Fisica, S•o Carlos, SP, Brazil 13560-970 (M.A.P.-D.-S.). Accepted for publication June 18, 2002. Synopsis A new method for morphological hair analysis at high resolution and under ambient conditions is presented in this paper. The AFM has been used in these experiments to analyze morphological changes in hair roughness and thickness after UV radiation. Through the powerful analytical AFM tools, changes in hair morphology can be proven. A new quantitative methodology to evaluate hair structure is presented in this paper. INTRODUCTION Constant investigations into technological development of hair care products that exceed consumers' expectance have long represented a challenge for researchers and scientists. Many investigations have been carried out to develop effective cosmetic products for human hair, and scientists have employed a variety of methods in their attempts to understand the alterations and to prove the cosmetic efficacy of the products. Recent reports on the harmful effects of sunlight on human skin have raised the aware- ness of the deleterious effect of sunlight on biological tissues in general. Hair can also suffer photo degradation (1), which can contribute significantly to overall hair damage (2). The influence of sunlight on untreated human hair has been extensively analyzed by examination of the protein, melanin, and lipid components as well as the morphological areas on irradiated hair (3). These studies have demonstrated that the physical and chemical modifications of hair are marked by intrinsic patterns of damage correlated to its pigmentation and to the amount and intensity of sunlight to which it has been exposed. UV-A and the visible part of sunlight (VIS) damage hair significantly however, hair's properties are also influenced to a minor extent by UV-B and IR irradiation. Black hair is largely protected from damage by the pigment eumelanin. In contrast, blonde 271