72 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ability, but surprisingly, the complex with a 6/10 ratio reverts to the previous high level of SPF (Figure 3). Dose-dependency of MDC-boehmite complex, which was fixed at a 1:1 ratio, was eval- uated with an Osram lamp. The SPF value increases with increasing concentrations, ranging from SPF 2 at 2% to SPF 7 at 10% (Figure 4). In combination with the ordinary UVB sunscreen Parsol MCX, protection factors ob- served with an SE lamp for human volunteers shows that MDC-boehmite (1/1) complex plus Parsol MCX bears an optimal combination in preventing UVB-induced erythema at a 6/2 ratio, exhibiting the highest value among combinations with a total of 8% (Figure 5). The same experiment using an Osram lamp reveals that a similar optimal combination of MDC-boehmite and Parsol MCX gives greatest protection (Figure 6). PREVENTIVE EFFECT OF MDC-BOEHMITE COMPLEX ON UVA-INDUCED PIGMENTATION UVA irradiation is well known to be a stimulant for noninflammatory pigmentation. Therefore, the prevention of pigmentation was examined on brownish yellow guinea pig skin over 22 days after daily two-hour exposure to UVA for eight days. UVA irradiation clearly produced distinctly visible pigmentation on the flank skin, which began to appear in seven days and increased its intensity for 22 days after cessation of exposure. Application of MDC-boehmite complex at 6% concentration of MDC signifi- cantly exhibits a marked preventive effect on the UVA-induced pigmentation over a period of 22 days (Figure 7). In order to know whether the observed decrease in the intensity of pigmentation by MDC-boehmite complex is caused by the interruption of PF a 6-0 6-2 6-4 6-6 6-8 6-10 6-12 MDC/Boehmite % Figure 3. Preventive effect of MDC-boehmite complex on SE lamp-induced erythema of human back skin. The skins were treated (2 mg/cm 2) with samples of W/O-type emulsion containing MDC-boehmite on five separate areas and ten minutes later were irradiated once with an SE lamp (0.41 mW/cm2). n = 6. PF = protection factor.

A NEW BROAD-SPECTRUM SUNSCREEN 73 7 q 6 -- PF 4- 3 0 2% 4% 6% 8% 10% MDC/Boehmite (1/1) Figure 4. Dose dependency of the preventive effect of MDC-boehmite (1/1) complex on Osram lamp-in- duced erythema of human back skin. The skins were treated (2 mg/cm 2) with samples of W/O-type emulsion containing MDC-boehmite (1/1) on five separate areas and ten minutes later were irradiated once with an Osram lamp (0.41 mW/cm2). n = 5. PF = protection factor. 5 0 0-8 2-6 4-4 6-2 8-0 MDC-Boehmite/P-MCX% Figure 5. Preventive effect of MDC-boehmite (1/1) combined with P-MCX on SE lamp-induced erythema of human back skin. The skins were treated (2 mg/cm 2) with samples of W/O-type emulsion containing MDC-boehmite (1/1) and P-MCX on five separate areas and ten minutes later were irradiated once with an SE lamp (0.41 mW/cm2). n = 5. PF = protection factor.