Abstract: A hair treatment method comprising steps [A-1], [B], and [C], wherein the method is carried out in the order of [A-1]?[B]?[C], or in the order of [B]?[A-1]?[C]: step [A-1]: a step of applying a first hair treatment agent comprising an organic acid having a solubility in 100 mL of water at 20° C. of 50 g or less or a salt of the organic acid, as component (A1), to hair, and rinsing the hair; step [B]: a step of applying a second hair treatment agent comprising a carboxylic acid having an inorganic value of 250 or more and 450 or less and an organic value of 50 or more and 250 or less or a salt of the carboxylic acid, as component (B), to the hair; and step [C]: a step of applying a third hair treatment agent comprising an aromatic sulfonic acid having a molecular weight of 300 or less or a salt thereof, as component (C), to the hair.

Abstract: A hair treatment method comprising steps (i) to (iii): step (i): a step of applying a hair treatment agent containing components (A) and (B) to hair; step (ii): a step of leaving the hair to stand, after step (i); and step (iii): a step of applying a hair treatment agent containing component (C) to the hair, after step (ii), (A) a compound selected from the group consisting of a glycylglycine derivative, a polyglycerin, and an alkyl glyceryl ether; (B) a carboxylic acid having an inorganic value of 250 to 450 and an organic value of 50 to 250, or a salt of the carboxylic acid; (C) an aromatic sulfonic acid having a molecular weight of 300 or less, or a salt thereof.

Abstract: A method for treating hair, comprising the following steps: step (i): a step of applying a first composition comprising carboxylic acid having an inorganic value of 250 to 450 and an organic value of 50 to 250, or a salt of the carboxylic acid, as a component (A), to hair, step (ii): a step of leaving the hair, to which the first composition has been applied, at a temperature of 15° C. to 100° C. for 15 seconds to 60 minutes, and step (iii): a step of applying a second composition comprising aromatic sulfonic acid or a salt thereof having a molecular weight of 300 or less, as a component (B), to the hair after completion of the step (ii).