EVALUATION OF SUNSCREEN FORMULATIONS 543 Figure 1. Scanning electron micrograph of dry film prepared from formulation containing acrylate polymer and sunscreen (X7750) held slightly above the skin's surface. It is our opinion that this type of protec- tion is superior to that provided by formulations in which the sunscreen sinks into the skin and the outer surfaces are no longer protected. Some of our early evaluations of these formulations were made on subjects who were showered under standardized conditions after application 'of lo- tions and then were exposed to uv lamps to determine burn resistance of treated areas. Three different lotions were applied to the right, center, and left backs. Ap- proximately 0.3 ml of lotion was applied to 16 in. 2 of skin. This area of the body was then placed under a shower with a wide spray head for 10 min. After air drying, the subject's back was exposed to a commercial uv lamp for approximately 15 min. The back had first been covered with a piece of fabric, sections of which were cut out to permit the lamp's rays to penetrate. Photo- graphs of the back with its small bumed spots were then taken 6 hours later. The degree of sunburn was rated by two observers examining the photo- graphs of 15 subjects exposed to this treatment and redness w. as rated on a

544 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 2. Scanning electron micrograph of sliced film shown in Fig. I (X7750) scale of 1 to 5, with 5 corresponding to extreme redness. The experimental formulation containing acrylate polymer will be called Formulation I and a commercial lotion containing homomenthyl salicylate will be called Commer- cial Suntan Lotion A. The average redness ratings obtained from these spot- burn tests are given in Table I and show the superior performance of Formu- lation 1. Table I Results of Spot-Burn Tests Product Average Redness Rating Formulation 1 1.3 Formulation 1 (no polymer) 2.7 Commercial Suntan Lotion A 2.9