The use is described of merocyanine derivatives of formula (1), wherein R1 and R2 are each independently of the other hydrogen; C1- C22alkyl; cyclo-C3C8alkyl; or unsubstituted or C1-C5alkyl- or C1-C5alkoxy- substituted C6-C20aryl; orl; or R1 and R 2 together with the nitrogen atom linking them form a -(CH2) m- ring which is uninterrupted or. interrupted by -O- or by -NH-; R3 is a cyano group; -COOR5; -CONHR5; -COR 5; or -SO2R5; R4 is a cyano group; - COOR6; -CONHR6; -COR6; or -SO2R 6; R5 and R6 are each independently of the other C1-C22alkyl; or unsubstituted or C1-C 5alkyl substituted C6-C 20aryl; or R3 and R4 together or R5 and R6 together form a 5- to 7-membered, monocyclic, carbocyclic or heterocyclic ring; Z1, and Z2 are each independently of the other a -(CH2),- group which is uninterrupted or interrupted by -O-, -S-, or by -NR 7-, and/or is unsubstituted or substituted by C,1-C 5 alkyl; R7 is C1C5alkyl; I is from 1 to 4; m is from 1 to 7; n is from 1 to 4; when n = 2, R1, R 5 or R6 is a bivalent alkyl group; or R1, and R 2 together with the 2 nitrogen atoms linking them form a -(CH 2)m- ring; when n = 3, R1, R5 or R 6 is a trivalent alkyl group; when n = 4, R1, R5 or R6 is a tetravalent alkyl group; and R1, and R 2 in formula (1) are not simultaneously hydrogen, in protecting human and animal hair and skin from UV radiation.