The invention relates to agents for the reductive decolorization of dyed keratin fibers, in particular human hair, containing in an aqueous cosmetic carrier (a) one or more reduction agents from the group consisting of sodium dithionite, zinc dithionite, potassium dithionite, sodium sulfite, sodium hydrogen sulfite, potassium sulfite, potassium hydrogen sulfite, ammonium sulfite, sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, hydroxymethanesulfinic acid, aminomethanesulfinic acid, cysteine, thiolactic acid, sulfanylacetic acid (thioglycolic acid), and/or ascorbic acid, and (b) one or more zwitterionic surfactants, each of which has at least one quaternary ammonium group and a grouping of —SO3— as structural units.
