Disclosed are: a hair treatment agent containing a glyoxylic acid and an alkyl ether carboxylic acid amino acid salt represented by general formula (I): R1-O-(CH2CH2O)nCH2COOM (I) (in the formula, R1 represents a saturated or unsaturated hydrocarbon group, n represents number of 1-10, and M represents lysine, histidine, or arginine.)； and a hair treatment method including a step of applying said hair treatment agent to the whole or a part of hair on the head.本案所揭示的是一種毛髮處理劑以及一種毛髮處理方法，前述毛髮處理劑包含通式(I)：R1-O-(CH2CH2O)nCH2COOM(I)(式中，R1表示飽和或不飽和烴基，n表示1~10之數，M表示離胺酸、組胺酸或精胺酸)所示之烷基醚羧酸胺基酸鹽及乙醛酸；前述毛髮處理方法包含將該毛髮處理劑應用到全部或一部分頭髪之步驟。
