A NEW BROAD-SPECTRUM SUNSCREEN 71 boehmite/MDC ratios. In the absence of boehmite, the MDC spectrum consists of two peaks in both UVA and UVB ranges, with higher UVB than UVA absorbance. The addition of boehmite causes the MDC spectrum to shift toward the UVA range (Figure lB). The molecular absorbance coefficient of MDC with increasing proportions of boehmite indicates that complexation with boehmite induces a marked increase in mo- lecular absorbance coefficient in the UVA range and a decrease in the UVB range, eventually rising above a twofold increase at 4/1 ratios (Figure 1C). Figure 1D shows a comparison with other UVA sunscreens. PREVENTIVE EFFECT OF MDC-BOEHMITE COMPLEX ON PUVA-INDUCED ERYTHEMA SPF evaluation of MDC-boehmite complex with several mixed ratios for PUVA treat- ment of guinea pig skin demonstrates that, parallel with changes in molecular absor- bance coefficient, an increase in boehmite ratio provides high efficacy of protection against PUVA reaction, which ranges from an SPF of 4 in the absence of boehmite to an SPF of 7.5 with a ratio of 6/10, despite the same 6% concentration of MDC. With a 6/12 ratio, a lower SPF value than that of a 6/10 ratio is observed due to solubility (Figure 2). PREVENTIVE EFFECT OF MDC-BOEHMITE COMPLEX ON UVB-INDUCED ERYTHEMA Evaluation of UVB-induced erythema on human skin reveals that MDC-boehmite com- plex possesses a distinct protection capability, with an SPF of 5 in the mixture ratio of 6/0 to 6/4. A high concentration of boehmite, exceeding 6%, decreases the protection PF 6-0 6-2 6-4 6-6 6-8 6-10 6-12 MDC/Boehmite % Figure 2. Preventive effect of MDC-boehmite complex on PUVA-induced erythema of guinea pig skins. Five guinea pigs received a topical application of O. 6% 8-methoxypsoralen in ethanol 30 minutes prior to UYA exposure (3.1 mW/cm2). The samples consisting of MDC-boehmite aqueous solution were applied at 2 mg/cm 2 concentration on five separate areas of the flank ten minutes prior to UVA exposure. PF = protection factor.

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.