The use is described of merocyanine derivatives of formula (1), wherein R.sub.1 and R.sub.2 are each independently of the other hydrogen; C.sub.1-C.sub.22alkyl; cyclo-C.sub.3C.sub.8alkyl; or unsubstituted or C.sub.1-C.sub.5alkyl- or C.sub.1-C.sub.5alkoxy-substituted C.sub.6-C.sub.20aryl; orl; or R.sub.1 and R.sub.2 together with the nitrogen atom linking them form a --(CH.sub.2).sub.m-- ring which is uninterrupted or, interrupted by --O-- or by --NH--; R.sub.3 is a cyano group; --COOR.sub.5; --CONHR.sub.5; --COR.sub.5; or --SO.sub.2R.sub.5; R.sub.4 is a cyano group; --COOR.sub.6; --CONHR.sub.6; --COR.sub.6; or --SO.sub.2R.sub.6; R.sub.5 and R.sub.6 are each independently of the other C.sub.1-C.sub.22alkyl; or unsubstituted or C.sub.1-C.sub.5alkyl substituted C.sub.6-C.sub.20aryl; or R.sub.3 and R.sub.4 together or R.sub.5 and R.sub.6 together form in a 5- to 7-membered, monocyclic, carbocyclic or heterocyclic ring; Z.sub.1, and Z.sub.2 are each independently of the other a --(CH.sub.2).sub.n-- group which is uninterrupted or interrupted by --O--, --S--, or by --NR.sub.7--, and/or is unsubstituted or substituted by C.sub.1-C.sub.5alkyl; R.sub.7 is (C.sub.lC.sub.5alkyl; 1 is from 1 to 4; m is from 1 to 7; n is from 1 to 4; when n=2, R.sub.1, R.sub.5 or R.sub.6 is a bivalent alkyl group; or R.sub.1, and R.sub.2 together with the 2 nitrogen atoms linking them form a --(CH.sub.2).sub.m-- ring; when n=3, R.sub.1, R.sub.5 or R.sub.6 is a trivalent alkyl group; when n=4, R.sub.1, R.sub.5 or R.sub.6 is a tetravalent alkyl group; and R.sub.1, and R.sub.2 in formula (1) are not simultaneously hydrogen, in protecting human and animal hair and skin from UV radiation. ##STR00001##