The present invention relates to bleaching composition for keratin fibres, especially human hair, comprising at least one compound with bleaching and/or highlighting effect and a magnesium salt. Further object of the present invention is the use of at least one magnesium salt in a bleaching and/ or highlighting composition for keratin fibres, especially for human hair, comprising at least one compound with bleaching and/or highlighting effect for preventing temperature increase going above 50°C, preferably above 45°C and more preferably above 40°C in a period of at least 60 min after mixing water free bleaching and/or highlighting composition and oxidizing lotion.
