PURPOSE: To obtain a hair cosmetic such as shampoo, hair rinse, hair conditioner and hair treatment giving excellent lasting softness to the hair by adding a β-hydroxymonosulfonic acid or its salt and optionally further a surfactant to a hair cosmetic.

CONSTITUTION: This hair cosmetic contains a β-hydroxymonosulfonic acid of the formula (R1 is H or 1-3C alkyl; X is H, metal atom or onium; R1 and X are not H at the same time) or its salt. The compound of the formula is e.g. isethionic acid salt or 2-hydroxypropanesulfonic acid salt. These compounds may be used singly or a combination of two or more compounds and the amount of the compound in the total composition is 0.01-20wt.%. The hair cosmetic is preferably further compounded with a surfactant to improve the feeling in use or imparting detergent force to the agent. The surfactant is e.g. polyoxyethylene lauryl ether sulfuric acid sodium salt. The amount of the surfactant to be compounded to the total composition is 0.1-50wt.%.