A multi-component package unit (kit-of-parts) for reductive decolourising of keratin fibers includes, separately packaged, a first container (A) comprising cosmetic agent (a) and a second container (B) comprising a cosmetic agent (b) that comprises (b1) one or multiple oxidizing agents chosen from the group of hydrogen peroxide, potassium persulfate, sodium persulfate and/or ammonium persulfate. The cosmetic agent (a) is thiourea (thiocarbmide). Most preferably, the container (A) further comprises monoethanolamine. Most preferably, (b1) is hydrogen peroxide. Also claimed are a ready to use agent for reductive decolourising of dyed keratinous fibres which comprises both thiourea and at least one of hydrogen peroxide, potassium persulfate, sodium persulfate and/or ammonium persulfate. Also disclosed are methods for reductive decolourising of dyed keratinous fibres which comprises mixing (a1) and (b1) with a further cosmetic agent and applying the mixture to dyed keratinous fibres (e.g. human hair).
