296 JOURNAL OF COSMETIC SCIENCE Table I DRT Values for Products Luna® SPF 12, 27, and 35, Tested at a Distance of 35 cm and 76 cm Away From the UV Lamp Luna® SPF 12 SPF 27 SPF 35 * Could not be determined. 35 2.9 114 184 Distance from UV lamp (cm) DRT (min) 76 19.3 * * products and their DRTs obtained microbiologically (Figure 3 and Table II). Photo­ derm® SPF 100 provided a high degree of photoprotection so that the DRT could not be reached. POTENTIAL APPLICATIONS OF THE MICROBIOLOGICAL METHOD The potentials of the method developed in this study as a quality control tool in the formulation phase of sunscreen product development were tested. For a single sunscreen test formulation containing BZ-3, increasing the sunscreen agent concentration from 1 % to 3% resulted in a proportional increase in the DR T (Table III). However, no further increase in the DR T was observed when the BZ-3 concentration was further 4 3.5 3 2.5 .5 E-� 1.5 1 0.5 0 0 50 100 150 200 250 300 Number of colonies/ plate Figure 2. Effect of the initial number of colonies per plate on the DR T of a commercial brand (Luna® SPF l 2).

.i::: bJ) UV SCREENING EFFECT OF SUNSCREENS 1.5 1 0.5 0 20 40 60 •Luna SPF 12 ♦ LtmaSPF 27 ■ LtmaSPF 35 x SpectraBAN SPF 55 • Photodenn SPF 100 80 100 120 Exposw·e time, min Figure 3. Log survivor plots of some marketed sunscreen products. 297 increased to 6%. Physical investigation by light microscopy of the test formulation containing 6% BZ-3 indicated separation of the sunscreen in the form of needle shape crystals (Figure 4). BZ-3 concentration most probably exceeds its solubility limit in the vehicle of this test formulation. The phenomenon of crystallization of the sunscreen agent in relatively concentrated formulations has been reported previously (18). Because Table II DRT Values of Some Marketed Sunscreen Products Product Luna® SpectraBAN® Photoderm® * Could not be determined. SPF label claim (in vivo) 12 27 35 55 100 DRT (h) 0.06 1.90 3.10 10.6 *