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.
