Described are merocyanine derivatives of formula wherein R2 is hydrogen; C1-C22alkyl; cyclo-C3-C8alkyl; unsubstituted or C1-C6alkyl- or C1-C6alkoxy-substituted C6-C20aryl; a cyano group; or R1 and R2 together with the nitrogen atom linking them form a —(CH2)m— ring which is optionally interrupted by —O— or by —NR7—; R4 is a cyano group; or -Q1-R5; Q1 is —COO—; —CONH—; —CO—; —SO2—; or —CONR6—; R5 is C1-C22alkyl; cyclo-C3-C8alkyl; or unsubstituted or C1-C6alkyl-substituted C6-C20aryl; R6 is hydrogen; C1-C22alkyl; cyclo-C3-C8alkyl; unsubstituted or C1-C6alkyl- or C1-C6alkoxy-substituted C6-C20aryl; R7 is hydrogen; C1-C22alkyl; cyclo-C3-C8alkyl; unsubstituted or C1-C6alkyl- or C1-C6alkoxy-substituted C6-C20aryl; the cyclohexene radical C is not substituted or substituted by one or more C1-C5alkyl; m is from 3 to 7; n is from 2 to 4; and o is from 2 to 4. Said merocyanine derivatives are useful in protecting human and animal hair and skin from UV radiation and to cosmetic compositions comprising said derivatives.