Process for semi-permanent straightening and dyeing hair: wherein the semi-permanent straightening comprises the steps of: a. optionally washing the hair with a cleansing composition and towel drying, b. applying to the hair a treatment composition A comprising at least one compound of the general structure R-CO-R' Formula and/or a hydrate thereof and/or a salt thereof, wherein R is selected from hydrogen, COOH, CN, optionally substituted C 1 -C 10 alkyl, optionally substituted C 2 -C 10 alkenyl, optionally substituted C 2 -C 10 alkynyl, optionally substituted C 3 -C 10 cycloalkyl, optionally substituted C 6 -C 10 aryl or a 5-10-membered, optionally substituted heteroaryl group, wherein the optional substituents of the alkyl group are selected from halogen, hydroxyl, amino and C 1 -C 4 alkoxy, and the optional substituents of the other groups are selected from halogen, hydroxyl, amino, C 1 -C 4 alkyl and C 1 -C 4 alkoxy, and R' is H or COOH, wherein the composition has a pH in the range of 1 to 4 when R' is COOH and in the range of 1 to 6 when R' is H, c. leaving the composition A on the hair for 1 min to 90 min, d. optionally rinsing off the hair, e. optionally drying the hair, f. heating the hair to a temperature in the range of 130°C to 230°C, g. optionally rinsing the hair, wherein the subsequent dyeing carried out immediately after the steps a to g comprises the steps of: h. optionally washing, towel drying the hair and optionally drying the hair, i. applying a ready-to-use composition onto the hair consisting of compositions B, C, and D, which are kept separately until application and mixed to a ready-to-use composition prior to application onto hair at a weight ratio in the range of 1:2:0.1 to 1:1:1 and left on the hair for 1 min to 45 min, and j. rinsing off the hair with water and/or optionally shampooing the hair, and k. optionally drying the hair wherein composition B is an alkaline aqueous composition comprising one or more hair dyes, one or more alkalizing agents and has a pH between 7.5 and 12, wherein the composition C is an acidic composition having a pH of 2 to 5 and comprising one or more oxidizing compounds, preferably hydrogen peroxide, and wherein the composition D is a composition comprising 1) one or more carboxylic acids having three or more carboxyl groups and/or their salts, and 2) one or more additional organic acid and/or their salts having one or two carboxyl groups, wherein composition D comprises the acids 1) and 2) and/or their salts at a total concentration of 10% to 100% by weight, calculated to the total of composition D, wherein the ready-to-use composition has a pH in the range of 6.5 to 12 and comprises the acids and/or their salts at a total concentration in the range of 1.0% to 10.0% by weight calculated to the total of the ready-to-use composition. a. optionally washing the hair with a cleansing composition and towel drying, b. applying to the hair a treatment composition A comprising at least one compound of the general structure R-CO-R' Formula and/or a hydrate thereof and/or a salt thereof, wherein R is selected from hydrogen, COOH, CN, optionally substituted C 1 -C 10 alkyl, optionally substituted C 2 -C 10 alkenyl, optionally substituted C 2 -C 10 alkynyl, optionally substituted C 3 -C 10 cycloalkyl, optionally substituted C 6 -C 10 aryl or a 5-10-membered, optionally substituted heteroaryl group, wherein the optional substituents of the alkyl group are selected from halogen, hydroxyl, amino and C 1 -C 4 alkoxy, and the optional substituents of the other groups are selected from halogen, hydroxyl, amino, C 1 -C 4 alkyl and C 1 -C 4 alkoxy, and R' is H or COOH, wherein the composition has a pH in the range of 1 to 4 when R' is COOH and in the range of 1 to 6 when R' is H, c. leaving the composition A on the hair for 1 min to 90 min, d. optionally rinsing off the hair, e. optionally drying the hair, f. heating the hair to a temperature in the range of 130°C to 230°C, g. optionally rinsing the hair, h. optionally washing, towel drying the hair and optionally drying the hair, i. applying a ready-to-use composition onto the hair consisting of compositions B, C, and D, which are kept separately until application and mixed to a ready-to-use composition prior to application onto hair at a weight ratio in the range of 1:2:0.1 to 1:1:1 and left on the hair for 1 min to 45 min, and j. rinsing off the hair with water and/or optionally shampooing the hair, and k. optionally drying the hair wherein composition B is an alkaline aqueous composition comprising one or more hair dyes, one or more alkalizing agents and has a pH between 7.5 and 12, wherein the composition C is an acidic composition having a pH of 2 to 5 and comprising one or more oxidizing compounds, preferably hydrogen peroxide, and wherein the composition D is a composition comprising 1) one or more carboxylic acids having three or more carboxyl groups and/or their salts, and 2) one or more additional organic acid and/or their salts having one or two carboxyl groups, wherein composition D comprises the acids 1) and 2) and/or their salts at a total concentration of 10% to 100% by weight, calculated to the total of composition D, wherein the ready-to-use composition has a pH in the range of 6.5 to 12 and comprises the acids and/or their salts at a total concentration in the range of 1.0% to 10.0% by weight calculated to the total of the ready-to-use composition. 1) one or more carboxylic acids having three or more carboxyl groups and/or their salts, and 2) one or more additional organic acid and/or their salts having one or two carboxyl groups,