The invention relates to a kit for lightening or whitening a keratinic material,preferably skin body surface, said kit comprising at least three separate elements:- an oxidizing composition, said composition comprising at least one oxidizing agentand at least one jellifying polymer- an activating composition comprising at least one alkali agent decomposing theoxidizing agent of said oxidizing composition and- a solid substrate.The invention relates to a method of cosmetic treatment for whitening or lightening akeratinic material.