The present invention relates to the use of dedifferentiated plant cells obtained from Bougainvillea as the active ingredient in a cosmetic composition. It also relates to the cosmetic compositions for topical application comprising such cells, to a cosmetic, non-therapeutic skin treatment method implementing such a cosmetic composition, and to the non-therapeutic use of a cosmetic composition for topical application comprising such cells for skin care, in particular for improving the firmness of the skin, in particular by promoting the regeneration of the skin dermis and epidermis.