A method of decolorizing human hair that has been dyed with an oxidation dye or partially oxidizing dyes comprising applying an agent comprising: in a cosmetic carrier, at least one compound according to Formula (I), where the substituents are as defined in the claims and where X represents a direct bond or a bivalent organic radical according to Formula (II) and where the total content of sulfur-containing compounds which are not the same as the compounds of Formula (I) is below 1.0 wt%. Preferred compounds according to Formula (I) are dithioerythritol (DTE) and dithiothreitol (DTT). Use of compounds according to Formula (I) for decolorizing human hair that has been dyed with oxidation dyes or partially oxidizing dyes. A kit of parts comprising preparations (A) and (B) that are packaged separately, where preparation (A) comprises, in a cosmetic carrier, at least one compound according to Formula (I), and where preparation (B) is hydrous and comprises at least one acid and/or at least one alkalizing agent.
