The invention relates to plant extracts for stimulating the synthesis of hyaluronan synthase, particularly the synthesis of hyaluronan synthase 2 (HAS2). Specific aims of the invention are to increase firmness and/or elasticity and/or tissue moisturization, and/or increase the skin barrier effect, and/or increase tissue resilience, and/or modulate angiogenesis, or the neocreation of blood capillaries, and/or improve healing, and/or cell proliferation, migration or differentiation, and/or skin atrophy, and/or intended to combat the effects of ageing on the skin, and in particular to combat the loss of firmness of the skin observed in the course of ageing, and/or atrophied scars.