Hair cosmetic method, including the phases of:a) applying a hair care and beauty treatment to the hair;b) supplying gaseous oxygen (O2) to the hair, simultaneously and/or subsequently to the hair care and beauty treatment,said hair care and beauty treatment being a hair colouring treatment,wherein the gaseous oxygen has a concentration higher than 80% (v/v) and the gaseous oxygen supply phase lasts between 2 and 20 minutes.