There is provided a composition comprising a peroxy ±-ketocarboxylic acid, which contains an acidic -OOH group, and at least one of a carboxylic acid corresponding to the peroxy ±-ketocarboxylic acid and an anion of the carboxylic acid corresponding to the peroxy ±-ketocarboxylic acid, wherein the acidic -OOH group of the ±-ketocarboxylic acid is replaced by a -OH group in the carboxylic acid corresponding to the peroxy ±-ketocarboxylic acid.