The subject of the invention is an agent for the permanent shaping of hair, characterized in that it contains as active keratin-reducing substance a compound in accordance with the general formula ##STR1## in which R.sub.1, R.sub.2 and R.sub.3 stand for H, carboxy or a straight- or branched-chain alkyl radical, monohydroxyalkyl radical or polyhydroxyalkyl radical with 1 to 6 carbon atoms respectively, on the condition thatnot all radicals R.sub.1 to R.sub.3 stand for H at the same time;if R.sub.1 and R.sub.2 stand for H, then R.sub.3 is carboxy or a branched alkyl, branched monohydroxyalkyl or branched polyhydroxyalkyl radical with 1 to 6 carbon atoms;if none of the radicals R.sub.1 to R.sub.2 stand for carboxy or have a branched alkyl, branched monohydroxyalkyl or branched polyhydroxyalkyl radical with 1 to 6 carbon atoms, then at least two of the radicals R.sub.1, R.sub.2 or R.sub.3 stand for a straight-chain alkyl, monohydroxyalkyl or polyhydroxyalkyl radical with 1 to 6 carbon atoms andif one of the radicals is carboxy, then the other two radicals are not carboxy at the same time.The agent allows for gentle, even shaping of the hair in a way that protects the skin and the hair, at a pH range of 6.5 to 9.5, without causing allergic and sensitizing reactions.