A NEW BROAD-SPECTRUM SUNSCREEN 75 melanocyte proliferation, melanocyte counts were carried out following split-dopa staining of irradiated skin. Melanocyte population analysis of the treated skin demon- strates that the number of dopa-positive melanocytes in the split epidermal sheet is markedly decreased compared with nontreated skin before irradiation, but some in- crease in melanocyte population is observed compared to nonexposed skin (Figure 8). PREVENTIVE EFFECT OF MDC-BOEHMITE COMPLEX ON UVB-INDUCED PIGEMENTATION Since the ability of sunscreens to suppress erythematous reaction does not necessarily parallel the ability to prevent pigmentation, pigmentation prevention was examined in brownish-yellow guinea pig skin over 22 days after daily exposure to UVB for three days. Several exposures to UVB light in doses less than 1 MED produce clear pigmen- tation on the flank skin that begins to appear in four days and increases its intensity for 22 days after cessation of exposure. Application of MDC-boehmite complex at 6% concentration of MDC exhibits a slight preventive effect on the UVB-induced pigmen- tation, with the effect being higher at lower concentrations of boehmite (Figure 9). Analysis of the melanocyte population of treated skin demonstrates that an increase in the melanocyte population is more significantly suppressed by the application of MDC- boehmite complex than in UVA, despite the visibly weak preventive effect on pigmen- tation (Figure 10). PREVENTIVE EFFECT OF MDC-BOEHMITE COMPLEX ON PROSTAGLANDIN E 2 RELEASE INDUCED BY PUVA Prostaglandin E 2 has been implicated frequently as an inflammatory mediator in ery- thema induced by UVB as well as PUVA irradiation (6). In order to determine the 2OO IOO LIV 5-0 6-2 6-8 6-10 6-12 C M I)C/Boehmltm % Figure 8. Effect of MDC-boehmite complex (MDC 6%, boehmite 0-12%) on the increased melanocyte population induced by UVA radiation.

76 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS UV 0 2 6 10 12 UV 0 2 6 10 12 UV 0 2 6 10 12 Boehmlte % Boehmlte % Boehmlte % 7 day 13 day 22 day Figure 9. Preventive effect of MDC-boehmite complex (MDC 6%, boehmite 0-12%) on UVB-induced hyperpigmentation of tortoiseshell guinea pig skin as revealed by color difference. The experimental an- imals were treated (2 mg/cm 2) with samples consisting of MDC-boehmite aqueous solution on five separate areas and ten minutes later were irradiated for five minutes with an SE lamp (1.4 mW/cm2). This process was repeated daily for three days. n = 7. AL = color difference. 7OO 2OO IOO 0 uv 6-0 6-2 6-6 6-10 6-12 c MDC/Boehmlt• % Figure 10. Effect of MDC-boehmite complex (MDC 6%, boehmite 0-12%) on the increased melanocyte population induced by UVB radiation.