The present invention relates to the cosmetic and / or nutraceutical use of an extract of the Lythrum salicaria plant and / or gallic acid and / or one of the gallic acid derivatives, in particular vescalagine and / or castalagine, more preferably castalagine, to maintain and / or increase expression of collagen in skin and / or mucous membranes to maintain and / or increase firmness of skin and / or mucous membranes and / or maintain and / or increase lipolysis in skin adipocytes to induce a skin slimming effect. and / or to diminish, prevent and / or treat the unsightly manifestations of cellulite, for example the orange peel appearance of the skin and / or the thigh appearance of the thigh. A further subject of the invention relates to the cosmetic care process comprising preferably topically applying lythrum salicaria extract according to the invention and / or gallic acid and / or one of the gallic acid derivatives, in particular vescalagine and / or castalagine, more preferably castalagine, or a cosmetic composition comprising it, to maintain and / or increase collagen expression in the skin and / or mucous membranes to increase the firmness of the skin and / or mucous membranes and / or to maintain and / or increasing lipolysis in skin adipocytes to induce a slimming effect on the skin and / or decreasing, preventing and / or treating the unsightly manifestations of cellulite, for example the skin's orange peel appearance and / or the appearance of the breech.a presente invenção refere-se ao uso cosmético e/ou nutracêutico de um extrato da planta lythrum salicaria e/ou do ácido gálico e/ou um dos derivados de ácido gálico, em particular vescalagina e/ou castalagina, mais preferencialmente castalagina, para manter e/ou aumentar expressão de colágeno na pele e/ou membranas mucosas para manter e/ou aumentar a firmeza da pele e/ou membranas mucosas e/ou manter e/ou aumentar lipólise nos adipócitos da pele para induzir um efeito de emagrecimento na pele e/ou para
