A hair treatment agent containing (a) 0.0001 to 20% by weight methionine； (b) 0 to 5% by weight maleic acid； (c) 0 to 5% by weight succinic acid, with the proviso that the total amount of ingredients (b) and (c) is 0.001 to 10% by weight in relation to the total agent； (d) at least one surfactant, is provided. The surfactant may be an amphoteric surfactant, an anionic surfactant or non-anionic surfactant. The agent may further contain a cationic polymer, preferably a cationic cellulose polymer and/or a cationic guar derivative. A method for the treatment of hair using said agent is outlined. Use of mixtures of (a) methionine； (b) maleic acid and/or succinic acid； (c) surfactant(s) to strengthen the inner hair structure and to increase the hair-conditioning effect of hair treatment agents is provided.
