Abstract: The invention relates to a method for individualizing the hair treatment of a consumer by personal supplementation of at least one benefit agent adding further functionality or enhancing existing functionality, or both, of a hair care composition, by the consumer. The method comprises the addition of a hair serum comprising said benefit agent to the hair care composition and the joint application to the hair of the consumer. The invention further relates to the provision of a kit comprising a hair serum and a packaging system.