The present invention relates to an optical H+-sensor, comprising an H+-indicator material, wherein the H+-indicator material is present between a support material and a H+-permeable layered structure, the layered structure comprising an H+-permeable hydrophilic layer and an H+-permeable cation exchange layer.Further, the invention relates to a method for determining the H+-concentration, e.g. expressed as pH, in a product or sample thereof, the method comprising contacting the product or sample with an optical H+-sensor according to the invention, measuring an optical property of the indicator material, and determining the H+-concentration of the product or sample based on said optical property.