The subject matter of the present disclosure are agents stabilizing keratin fibers comprising a cosmetic carrier and : (a) at least one compound of formula (I) wherein: x denotes oxygen (-O-), sulphur (-S-) or a grouping -NR5-,R1, R2, R3, R4 denote independently a hydrogen atom, a C1-C6-alkyl group, a C2-C6-alkenyl group, a hydroxyl-C1-C6-alkyl group, a C2-C6-alkanoyl group, a carboxyl group, a C1-C6-alkoxy-carbonyl group, a halogen atom, an aryl group, an aryl-C1-C6-alkyl group or the grouping Y, R5 denotes a C1-C6-alkyl group, a C2-C6-alkenyl group or an aryl group, Y denotes a grouping of the formula (II), R6,R7 denote independently a hydrogen atom, a C1-C6-alkyl group, a C2-C6-alkenyl group, a halogen atom, a hydroxyl-C1-C6-alkyl group, a C2-C6-alkanoyl group, a carboxyl group, a C1-C6-alkoxy-carbonyl group, a carbamoyl group, a C1-C6-alkylaminocarbonyl group or a di(C1-C6)alkylaminocarbonyl group. Also disclosed is a kit of parts for the lightening of keratinic fibers that comprises at least one compound of formula (I).
