A sensor (10; 34) for measuring and/or detecting fouling that forms directly or indirectly on a so-called front surface of the sensor, includes the following in the form of a plurality of superimposed layers: —at least one heating element (14) that is able to diffuse, on command, a homogenous, monitored heat flow whose heat output is less than 200 mW, —a heat insulator (11) located on the side opposite the front surface of the sensor to prevent dissipation of the heat flow from the opposite side, —at least one temperature measuring element (16) that is placed in the homogenous heat flow diffused by the at least one heating element and that offers a precision of temperature measurement of better than 0.1° C., and —a substrate (12; 42) on which the layers of the at least one heating element and at least one temperature measuring element are connected.