The use of compounds of the formula I in which R1 and R2 are identical or different, electron-withdrawing radicals chosen from the group consisting of cyano, alkyl- or arylcarbonyl, alkyloxy- or aryloxycarbonyl and optionally substituted aminocarbonyl, R3 is a hydrogen atom, a C1-C20-alkyl radical or a C3-C20-cycloalkyl radical or a radical of the formula —CH2—CH2—SO3—M+, where M+ is a cation, X is the divalent radical of oxygen, sulfur or the radical where R3 is as defined above, is the divalent radical of the formula II or III, which forms a fused system with the radical of the formula I where R4 can be bonded one or more times to the benzylidene ring I or naphthylidene ring II, and is hydrogen, alkyl, cycloalkyl, alkyloxy, cycloalkyloxy, alkoxycarbonyl, mono- or dialkylaminocarbonyl, alkylamino, dialkylamino, each having up to 20 carbon atoms, and also cyano, amino and SO3—M+, where M+ is a cation, as photostable UV filters in cosmetic and pharmaceutical preparations to protect human skin and human hair against solar rays, alone or together with compounds which absorb in the UV region and are known per se for cosmetic and pharmaceutical preparations.