The invention relates to the use of an active principle originating from Piper nigrum as a cosmetic firming active principle, particularly to combat laxity in photo-aged skin. The invention also relates to a specific active principle originating from Piper nigrum berries, as well as to cosmetic compositions containing said active principle and to a cosmetic skin-care method for firming the skin, in particular acting on the functionalities and the synthesis capabilities of the reticular dermis.