Disclosed are thiol dyes of formula (I), wherein R 1 , R 2 , R 3 , R 4 and R 5 independently from each other are hydrogen; unsubstituted or substituted, straight-chain or branched, monocyclic or polycyclic, interrupted or uninterrupted C 1 -C 14 alkyl; C 2 -C 14 alkenyl; C 6 -C 10 aryl; C 6 -C 10 aryl-C 1 -C 10 alkyl; or C 5 -C 10 alkyl(C 5 -C 10 aryl); A is a residue of an organic dye; and Y 1 is the direct bond; C 1 C 10 alkylene; C 5 -C 10 cycloalkylene; C 5 -C 12 arylene; or C 5 -C 12 arylene- (C1-C 10 alkylene). The compounds are used to dye hair with or without reducing agents. Furthermore, the present invention relates to compositions comprising thiol dyes of formula (I) and to process for the preparation of theses compounds.