Process for semi-permanent hair straightening and aftercare treatment, which comprises the following steps, performed in this order: (a) application of a straightening composition onto the hair, (b) leaving the composition on the hair for 1 to 120 minutes; (c) optionally rinsing off the hair; (d) drying the hair, (e) treating the hair with an iron having a surface temperature of 130 to 250°C, (f) optionally rinsing off and/or shampooing the hair and drying; (g) treating the hair with a one or both of a cleansing composition and a conditioning composition, wherein - the straightening composition has a pH of 4 or lower, preferably 1 to 3, more preferably 1 to 2.5, and comprises glyoxylic acid and/or a hydrate thereof and/or a salt thereof, preferably at a concentration in the range of 0.1 to 40% by weight, preferably 0.5 to 30% by weight, more preferably 1 to 25% by weight, most preferably 2.5 to 20 % by weight based on the weight of the total composition; - the cleansing composition has a pH of 4 or lower, preferably 1.5 to 4.0, more preferably 2 to 3.5, and comprises one or more surfactants selected from anionic, non-ionic and amphoteric surfactants and glyoxylic acid and/or a hydrate thereof and/or a salt thereof; the concentration of the glyoxylic acid and/or a hydrate thereof and/or a salt thereof preferably being in the range of 0.1 to 5% by weight, more preferably 0.2 to 4% by weight, based on the weight of the cleansing composition; and - the conditioning composition has a pH of 4 or lower, preferably 1.5 to 4.0, more preferably 2 to 3.5, and comprises one or more conditioning components and glyoxylic acid and/or a hydrate thereof and/or a salt thereof; the concentration of the glyoxylic acid and/or a hydrate thereof and/or a salt thereof preferably being in the range of 0.1 to 5% by weight, more preferably 0.2 to 4% by weight, based on the weight of the conditioning composition. (a) application of a straightening composition onto the hair, (b) leaving the composition on the hair for 1 to 120 minutes; (c) optionally rinsing off the hair; (d) drying the hair, (e) treating the hair with an iron having a surface temperature of 130 to 250°C, (f) optionally rinsing off and/or shampooing the hair and drying; (g) treating the hair with a one or both of a cleansing composition and a conditioning composition, - the straightening composition has a pH of 4 or lower, preferably 1 to 3, more preferably 1 to 2.5, and comprises glyoxylic acid and/or a hydrate thereof and/or a salt thereof, preferably at a concentration in the range of 0.1 to 40% by weight, preferably 0.5 to 30% by weight, more preferably 1 to 25% by weight, most preferably 2.5 to 20 % by weight based on the weight of the total composition; - the cleansing composition has a pH of 4 or lower, preferably 1.5 to 4.0, more preferably 2 to 3.5, and comprises one or more surfactants selected from anionic, non-ionic and amphoteric surfactants and glyoxylic acid and/or a hydrate thereof and/or a salt thereof; the concentration of the glyoxylic acid and/or a hydrate thereof and/or a salt thereof preferably being in the range of 0.1 to 5% by weight, more preferably 0.2 to 4% by weight, based on the weight of the cleansing composition; and - the conditioning composition has a pH of 4 or lower, preferably 1.5 to 4.0, more preferably 2 to 3.5, and comprises one or more conditioning components and glyoxylic acid and/or a hydrate thereof and/or a salt thereof; the concentration of the glyoxylic acid and/or a hydrate thereof and/or a salt thereof preferably being in the range of 0.1 to 5% by weight, more preferably 0.2 to 4% by weight, based on the weight of the conditioning composition.