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J. Cosmet. Sci., 67, 167–173 (May/June 2016) 167 Analysis of octyl methoxycinnamate in sunscreen products by a validated UV-spectrophotometric method MAYUREE KANLAYAVATTANAKUL, NATAMON KASIKAWATANA, and NATTAYA LOURITH, School of Cosmetic Science, Mae Fah Luang University, Chiang Rai 57100, Thailand. Accepted for publication May 30, 2016. Synopsis An inexpensive, rapid method for the determination of octyl methoxycinnamate (OMC) in sunscreen products using ultraviolet-spectrophotometry has been developed and validated according to International Council for Harmonisation and Association of Offi cial Analytical Chemists guidelines. Methanol was the optimal solvent used with a linearity range of 4–12 μg/ml (r = 0.999) being obtainable. The accuracy of the method is highlighted by the % recovery (98.23–98.50) and relative standard deviation (%RSD, 0.12), and it is widely applicable to prototype products composed of oil in water, and water in oil emulsions. Mineral oils containing low, intermediate, and high OMC levels (1%, 4%, and 7.5%) gave recovery percentages of 99.76–100.76 with %RSD of 0.02–0.28. In addition, this method is repeatable and affords a high degree of precision (%RSD = 0.12 and 0) with 96.08–99.27% recovery. The method is suitable for quality assurance of suncare product formulations, and could be applicable to product development and validation. INTRODUCTION Application of sunscreen products is widely recommended to protect against the harmful effects of ultraviolet (UV) radiation on skin (1), such as erythema, edema, and hypopig- mentation, which alters its aesthetics, and accumulative damage which can result in mel- anoma (2). The UV fi ltering agents in sunscreens are commonly classifi ed as organic or inorganic, in relation to their skin protection mechanism. The most commonly used UV fi lter is octyl methoxycinnamate (OMC also listed as ethylhexyl p-methoxy cinnamate or octinoxate). Exposure of OMC to solar radiation generates reactive chemical species in- cluding free radicals. If OMC is present in sunscreens, there is a potential for accumula- tion of free radicals in tissue, giving rise to adverse effects (3). Accordingly, the maximum allowable concentrations of OMC in sun protection products are 10% and 7.5%, as stated in European Union and U.S. Food and Drug Administration regulations, respectively (4). The presence of sunscreen agents in topical products is necessary to ensure their skin damage protection effi cacy, although such formulations must also be stable (5) and meet Address all correspondence to Mayuree Kanlayavattanakul at mayuree@mfu.ac.th.