The present disclosure relates to a cosmetic composition comprising at least one fluorescent dye comprising at least one fluorescent compound, and at least one cationic polymer with a charge density of at least 1 meq/g; processes that incorporate this cosmetic composition and to a kit comprising this cosmetic composition. The present disclosure also relates to the process for dyeing human keratin materials, including artificially dyed or pigmented hair and dark skin, with a lightening effect, comprising applying to the keratin materials a cosmetic composition comprising at least one fluorescent dye comprising at least one fluorescent compound and at least one cationic polymer with a charge density of at least 1 meq/g.