SUNSCREEN TESTING METHODS 809 too 80 6o 3000 \ WHITE WAX • •E.DIU• (Erylhemic} U.V. •,,• m LON• U.V. il 3200 A• 3000 ,•000 3000 ,•000 SOLUT!O'H 1•0•g%1 F$gure 1. Spectrophotometric tests (Shade Coppertone) ::• t :.a .s .s Figure 2. Spectrophotometric tests (Sea and Ski)

810 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS then cut to conform to a side of a cuvette and are appended by tape. The control cuvette is similarly dressed but without sunscreen on the paper. A possible drawback of this technique is that oily substances make paper somewhat translucent and therefore may give low absorption readings. Another variable might be the adherence or interaction of sunscreens and paper. Interactions could be monitored by change in form of the absorption curves compared to those of Method #l. Such changes did not occur. Method #$ This method is similar to #2, but employs waxed paper which is tan, to approximate more closely the lipid and pigment-containing surface of the epidermis. The same criticisms apply as in Method #2. Method #4 The procedure uses 10 mg% solutions of suspensions of whole product and evaluates absorption against the solvent control. Titanium- and zinc-containing products are incompletely dissolved and are shaken to cloudiness immediately before measuring. A major criticism is that solubilization may change the product and its light absorption char- acteristics however, absorption curve form did not change, and so it is unlikely that the absorber was changed. Method #6 This method attempts to simulate bathing after application of a sunscreen. A 50-ml beaker containing tap water at 28øC and a magnetic bead is placed on a magnetic stirrer and the water is gently agitated. Strips saved from Method #2 are placed into the bath for 5 minutes, dried 1,5 minutes, and applied to the side of a cuvette. Controls are white strips similarly wetted and dried but containing no sunscreen. Signifi- cant differences in light absorption have been noted after bathing the white paper. The major criticism is that the incorporation of sunscreen into white paper and its release by swirling water may be different from its binding to and release from the stratum corneum. Moreover, this test is dependent on the accuracy of Method #2. Results and Discussion Spectrophotometric Methods Absorption of mid and far ultraviolet light (2900-4000 •-) was deter- mined for each substance by the five testing methods. Products were