The present invention relates to a process for treating hair, especially human hair, wherein the hair is bleached and dyed in a subsequent order with compositions providing improved and milder bleaching and dyeing of hair. The inventors of the present invention have unexpectedly found out that when commonly used bleaching compositions and oxidative dyeing compositions are mixed with another composition comprising predominantly carboxylic acids, the bleaching and dyeing effects of the compositions are improved, homogeneous bleaching and dyeing of hair fibers is achieved and natural cosmetic properties of hair is maintained.
