Use of 2-hydroxy-4-methoxybenzophenone-5-sulphonic acid or its salts for protecting the hair against environmental attacking agents, and especially against light,and process for protecting the hair using this compound.The present invention relates to the use of 2-hydroxy-4-methoxybenzophenone-5-sulphonic acid and its salts as agents for protecting the keratin of the hair against environmental atta