The present invention relates to a cosmetic method for increasing collagen gene and/or protein expression comprising topically applying an effective amount of an extract of the plant Quassia amara onto skin and/or mucous membranes. The present invention relates as well to a cosmetic method comprising topically applying an effective amount of such an extract for increasing the firmness of skin and/or mucous membranes of an individual in need thereof. The present invention also relates to a method of cosmetic care comprising topically applying a composition comprising an effective amount of the extract of Q. amara onto skin and/or mucous membranes, for increasing the collagen gene and/or protein expression.
