10 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS MATERIALS and METHODS METHOD FOR DETERMINING SPF WITH NATURAL SUNLIGHT Guinea Pig Studies Studies were conducted on 100 male albino guinea pigs of Hartley strain 8 to 10 weeks of age. On the average, a group of 10 guinea pigs were used for testing each sunscreen preparation. The depilated back was sectioned off into three columns with cloth-tape. Then each test preparation was applied uniformly to an area of the back measuring 2cm x 9cm in a concentration of 2mg/cm 2 or 2/zg/cm 2. Test material was not applied in the central column for determining the untreated control MED value. Then 6 to 8 slots were made with cloth-tape, each slot covering an area of lcm x lcm. Exposures were given 15 minutes after application. Each exposure in a series was increased in a geometrical progression, i.e., each exposure was 30% greater than the previous exposure. The initial exposure for the series was selected on the basis of previous experience. At the end of each exposure period, one of the slots was covered in the control and test area to stop the exposure at that site. The duration of each exposure was monitored by means of a Sunburn Ultraviolet Integrator for administering a series of uniform and reproducible exposures to natural sunlight despite the variations produced by atmospheric condi- tions. Human Subject Studies This procedure is basically the same as that set forth in FDA's proposed rules. Studies were conducted on 73 healthy, fair-skinned and medium-skinned Japanese male volunteers 16 to 38 years of age (2). On the average, 20 subjects were used for each sunscreen preparation. The untanned mid-back was used for testing. The back was sectioned off into 6 columns with rubber plates so that each covered an area of 2.5cm x 32cm. Then each test preparation was applied to each column. Test material was not applied in one of the columns in order to determine the untreated control MED value. 8 slots were made with cloth-tape, each slot covering a 2.5cm x 3cm area. Field tests with guinea pigs and human subjects were performed at the same time in Okinawa, which is located at 26 degrees North latitude. Sunburn Ultraviolet Integrator ( SU- Integrator ) The relationship between the spectral sensitivity of SU-Integrator and erythema action spectra of guinea pigs and human subjects which was determined by using monochro- mator are shown in Figure 1. It may be seen that the SU-Integrator has a spectral sensitivity between 290nm and 330nm similar to the erythema action spectra of guinea pigs and human subjects (3,4). This instrument was found to be suitable in monitoring the study of sunscreen efficacy testing with natural sunlight. MED and SPF MED is the abbreviation for Minimal Erythema Dose. It is defined as the amount of energy required to produce a minimal perceptible erythema response approximately 20 hours after exposure and it is used as an index of sensitivity to UV irradiation.

ANIMAL MODEL FOR EVALUATION OF SUNSCREENS 11 100. Global solar radiation 0.1 300 310 320 330 340 350 360 370 360 390 400 nm Wavelength (nm) Figure 1. Spectral sensitivity of the Sunburn Ultraviolet Integrator. *Human Subjects **Guinea Pigs. SPF is an abbreviation for Sun Protection Factor. It is a number which designates to what extent a particular sunscreen preparation will allow the user to withstand the effects of ultraviolet radiation without developing an erythema. In this test, the test sites were examined approximately 20 hours after exposure, and each MED for unprotected skin and protected skin was read. The SPF was determined for each individual as follows: SPF = MED of protected skin MED of unprotected skin The individual SPF values were used to determine a mean SPF for the preparation. Model Sunscreen Preparations Model sunscreen preparations tested in this study, and the content of major UV-absorbers and UV-scatterers are shown in Table I. The preparations included 3 lotions, 3 oils, 3 creams, 2 oily powder sticks and 1 solid powder cake formulated with commonly used chemical absorbers and physical blockers. Here, lotion B is 8% homosalate lotion which was used as a standard sunscreen. METHOD FOR DETERMINING SPF WITH ARTIFICIAL SUNLIGHT In addition to the field testing, an attempt was made to establish a laboratory testing procedure with guinea pigs by using artificial sunlight. This test was performed in principle in the same procedure as natural sunlight. There are a few differences.