The present invention relates to the use of one or more salts of dihydroisoquinolinium for the treatment of keratinous substances, in particular keratin fibres, in particular human keratin fibers such as the hair. The present invention also relates to a process for treating keratin materials, using the said salts, and optionally in the presence of one or more chemical oxidizing agents. The present invention also relates to a composition for the lightening of the keratin materials, comprising one or more salts of dihydroisoquinolinium such as defined above - after and one or more chemical oxidizing agents.
