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]. Cosmet. Sci., 59, 291-302 CTuly/August 2008) Microbiological assessment of the ultraviolet screening effect of sunscreen preparations YASMINE A. GOMAA, ELSAYED ABOULMAGD, NABILA A. BORAEI, INAS A. DAR WISH and LABIBA K. EL-KHORDAGUI, Departments of Pharmaceutics (Y.A.G., N.A.B., I.A.D., L.K.E.-K.) and Pharmaceutical Microbiology (E.A.), Faculty of Pharmacy, University of Alexandria, El-Khartoum Square, Azarita, Alexandria 215 21, Egypt. Accepted for publication February 11, 2008. This paper was presented as a poster in the Industrial Pharmacy section at the International Pharmaceutical Federation (PIP) Congress, Cairo, 2005. Synopsis The purpose of this study was the development of a microbiological method for the assessment of the ultraviolet (UV) screening effect of sunscreen preparations and determination of their sun protection factor. The method is based on the lethal effect of UV radiation on Escherichia coli (E. coli) and the protective ability of sunscreens. The time of UV exposure required for the reduction of the E. coli viable count by 90% (decimal reduction time, DRT) was used as the photoprotection assessment parameter. The method was tested by assessing the effect of selected experimental variables on the DRT. The suitability of the method as a quality control tool for sunscreen preparations was then checked by assessing the influence of selected formulation variables on the photoprotective effect of a series of o/w emulsion formulations with different compositions. The method proved valid for detecting changes in the photoprotective effect of a market sunscreen product as a result of modifying experimental conditions. It also proved valid for ranking market sunscreen products according to their UV screening effect. Equally important, the method could successfully detect changes in the photoprotective effect of sunscreen test formulations as a function of the concentration and type of the sunscreen agents. INTRODUCTION Determination of the photoprotective effect of sunscreen products is based on the as­ sessment of the photoprotection provided by such products against the erythemogenic effect of UVB radiation on human subjects. This test is performed according to the guidelines developed by the FDA (Food and Drug Administration) (1), COUP A (Eu­ ropean Cosmetic Toiletry and Perfumery Association) (2), the Australian Standard (3), and the Japanese Norm (4). Despite the many disadvantages of the in vivo methodology, Address all correspondence to Yasmine A. Gomaa. 291