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j. Soc. Cosmet. Chem., 41, 67-84 (January/February 1990) Efficacy of 4-methoxydibenzoylmethane-2-carboxylic acid as a new broad-spectrum sunscreen GENJI IMOKAWA, TORU TEJIMA, NORIHARU KIRII, and MICHIO KAWAI, Tochigi and Tokyo Research Laboratories, Kao Corporation, Tochigi and Tokyo, Japan. Received March 1, 1989. Synopsis 4-Methoxydibenzoylmethane-2-carboxylic acid (MDC) was developed as a new sunscreen agent that is characterized by varying UVA and UVB absorption spectra with the cationic metal compound, boehmite. For protection against UVA, MDC-boehmite complex demonstrates a remarkable preventive effect on PUVA-induced erythema and UVA-induced pigmentation. Further study on protection against UVB or natural sunlight reveals that MDC-boehmite complex also possesses a distinct protective effect against UVB- or sunlight-induced skin reactions including erythema, pigmentation, and immediate tanning, and that its protective effect is markedly enhanced in an optimal combination with the ordinary UVB sunscreen Parsol MCX. This preventive effect is corroborated by the fact that prostaglandin release induced in organ culture after PUVA or UVB (PUVA = 8-methoxypsoralen and ultraviolet-A radiation) exposure is also significantly suppressed by the application of MDC-boehmite complex. Based on these findings, MDC is found to be useful for preventing several adverse effects of exposure to sunlight. INTRODUCTION The UVA waveband has been an important subject of research on the protection of skin from damage caused by sunlight because several cutaneous effects of ultraviolet irradia- tion including wrinkles, pigmentation, and skin cancer are found to be attributable to not only UVB but also UVA exposure (1-4). It is well known that the best way of protecting skin from sun damage is to apply sunscreens. Many UVB filters are now commercially available, but very few UVA filters have been developed. Since it is not practical to use a UVA filter only, the combination of UVB and UVA filters is always recommended for sunscreen formulations. Thus, it is desirable to develop a UV filter that absorbs radiation in both UVB and UVA wavebands. For evaluation of the efficacy of sunscreens, many studies have focused on a sun protection factor that is mainly based on an erythematous reaction induced by UV irradiation. Since an erythematous reaction is a result of complex and elaborative biological reactions, it is also worthwhile to evaluate the beneficial effect of sunscreens on other biological events following UV exposure. In the present study, by measuring SPF values as well as the inhibitory effect on pigmentaion and prostaglandin synthesis, we evaluated the effectiveness of a broad- spectrum UV sunscreen that is capable of absorbing both UVB and UVA wavebands. 67