J. Soc. Cosmetic Chemists, 18, 143-147 (Mar. 4, 1967) Evaluation of Sunscreen Agents V. DAS GUPTA, M.S.* Syno•sis--A new method for the evaluation of sunscreen agents is presented. The method is based on Urbach's che•nical ultraviolet exposure-meter syste•n (1). For the sake of co•n- parison, ultraviolet absorption values of the compounds tested are also reported. INTRODUCTION It is known that ultraviolet solar rays with a wavelength of from about 2900 to 3000 A cause severe burning of human skin upon over- exposure. To diminish the burning and protect human skin, ultraviolet light absorbing compounds are added to lotions, aerosols, and creams that are applied to the human body. A list of various ultraviolet light- absorbing compounds has been tabulated by Giese et al. (2). Subse- quent research dealing with sunscreen products has been directed toward the studies of sunscreen agents themselves, their vehicles, and the devel- opment of methods for their evaluation. New formulations are appear- ing on the market regularly, and, in many instances, superior sunscreen properties are claimed. Thus, the development of an in vitro method for testing the efficiency of these products in their final form would enable one to make comparisons. Giese et al. (3) used the skin of the arm or abdomen of human subjects for evaluation of sunscreen agents. They reported that the minimal erythemal dosage varies from individual to individual, depend- ing upon previous exposure and the type of skin. Knox (4) used the abdomen of the albino rabbits in his studies but noted the same dis- advantage of nonuniformity of response. The inherent variations en- countered when employing human subjects or rabbits render tests on * School of Pharmacy, The University of Georgia, Athens, Ga. 30601. 143

144 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS living subjects difficult to evaluate. Admittedly, fairly good data can be obtained through large scale field testing of human subjects. How- ever, this is an expensive and time consuming procedure. Parke and Sperandio (5) published a photographic method of eval- uation which is too complicated for routine use in the laboratory Riegelman (6) reported that the absorption spectrum can vary with the solvent used. In the final form of the formulation, a common solvent for spectrophotometric testing may not be easy to find. Thus, the need for a simpler and reliable method for the evaluation of sunscreens would appear to be welcome. EXPERIMENTAL Materials and Equipment 1. Urbach's System: A mixture of 62 mg methyl yellow, 120 mg hexachlorocyclopentadiene, 10 mg dibenzylamine, and 447 g Aloe's wax paraplast* is prepared as [ollows: The wax is melted and the other ingredients are added. The melt is poured into Petri dishes and allowed to cool before use. These dishes should be kept away from direct light. Upon exposure of this system to uv light, a free halogen radical is liberated from hexachlorocyclo- pentadiene which then combines with hydrogen to form an acid. The pH indicator, methyl yellow, then responds to changes in the acidity by turning from yellow to red. Thus, the amount of color change (from yellow to red) is a measure of incidental ultraviolet radiant energy absorbed by the system (7). 2. Brass Plate: This plate is slightly shorter than the size of the Petri dish and is about 167 u thick. A circular hole is cut in the center, and eight more holes surround the central one (hole radius approxi- mately 6 mm). The outside holes are numbered from one through eight. 3. Westinghouse Fluorescent Sunlam pt: This 20-watt lamp has an approximate range of 2.q00 to 3500 A, with a peak at approximately 3100 A. Minimum energy output is 47 •w/cm 2 at 1 m. Erythema is produced by this lamp in 140 seconds, whereas average sun produces it in 762 seconds. 4. Beckman DB Spectrophotometer with Sargent Recorder: All spec- tral curves were obtained with this instrument. Concentration of each compound was 0.0015% in methanol. Red Veterinary Petrolatum was * Available from Aloe's Scientific Co., 1831 Olive St., St. Louis, Mo. t Westinghouse lamp number S.S.20.