The invention relates to a composition for photodynamic therapy. The composition of the invention, in the form of a gel or a cross-linked hydrogel, includes a chlorophyll photosensitising substance or a derivative thereof, in particular chlorophyllin optionally associated with an additional ingredient such as an alpha- or beta-hydroxy acid, a depigmentation or lightening agent, and/or an antioxidant. The invention can be used in the treatment of skin aging signs and in skin regeneration.