a composition for treating hair comprised of a thiol compound that is a superior hair reductant and hair cosmetic , especially in terms of waving effect , odor , hair damage , texture and safety and where the thiol compound has the formula hs -- n -- nh --- m - nh2 and the n and the m are integers from 1 to 4 . the composition may include the salts of the compound . the composition is useful for a method of treating hair by applying the composition to the hair ; leaving the composition on the hair for a sufficient period of time , depending on the desired effect ; and then removing the composition . the invention , in particular , relates to hair reductants as well as primary agents for permanent waving , pretreatment agents for hair dyeing , cosmetics for heated hair curling , cosmetics for frizzy hair and cosmetics for human hair removing .