Provided are hair processing agents capable of permanent waving hair even at a neutral to weakly acidic pH range that causes less irritation to the skin, and hair processing agents in which an unpleasant odor is masked. Hair processing agents contain at least one compound represented by the formula (2). Hair processing agents contain a compound of the formula (2) and at least one compound (ii) selected from thioglycolic acid, thiolactic acid, cysteine, acetylcysteine, cysteamine, acylcysteamine, salts thereof and ester derivatives thereof. Hair processing agents contain a compound of the formula (2), a surfactant and water, and are emulsified. Hair processing agents contain a compound of the formula (2) and a specific perfume. wherein X is a structure selected from —O—, —S—, —NH— and —NR1—; R1 is an alkyl group of 1 to 6 carbon atoms; Y is an oxygen atom or a sulfur atom; in the formula (1), Z is a divalent organic residue having at least one mercapto group; in the formula (2), R is a divalent organic residue optionally having a mercapto group; and R2 is a hydrogen atom or an alkyl group of 1 to 6 carbon atoms.