The use of benzotriazole UV absorbers of formula (1), wherein A is a radical of formula (1a); (1b); or (1c); B is a radical of formula (1d); (1e); (1f), (1g); (1h); (1i); (1k); (1l); (1m); or (1n); R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are each independently of the others hydrogen, C.sub.1 C.sub.16alkyl; C.sub.5 C.sub.7cycloalkyl; halogen; R.sub.9 is hydrogen, C.sub.1 C.sub.12alkyl; or C.sub.5 C.sub.7cycloalkyl; R.sub.7, R.sub.8 and R.sub.10 are each independently of the others hydrogen, C.sub.1 C.sub.12alkyl C.sub.5 C.sub.7cycloalky, C.sub.1 C.sub.12hydroxyalkyl; X is halogen; a radical of formula (1s); (1t); or (1u); sulfate, phosphate, lactate, citrate, tartrate; R.sub.11 is C.sub.1 C.sub.12alkyl; or C.sub.5 C.sub.7cycloalkyl; R.sub.12 and R.sub.13 are each independently of the other hydrogen; or C.sub.1 C.sub.5alkyl; x is from 0 to 10; and y is from 1 to 20; in the cosmetic treatment of human hair for protection against UV radiation is described.