The invention relates to a moisture sensor which comprises a receiving area on its surface for a moisture film, the layer thickness of which is dependent on the relative humidity in the surrounding of the receiving area. The moisture sensor has a signal source which is connected to at least one control electrode at at least one infeed, the electrode abutting the receiving area, for providing a control voltage to the moisture film. The moisture sensor comprises at least one potential sensor which has at least one sensor area, under the receiving area, which is spaced apart from the at least one infeed. The sensor area is electrically insulated from the receiving area by an insulation layer, located between the sensor area and the receiving area, in such a way that an electrical potential can be capacitively detected by means of the potential sensor, the potential being dependent on the layer thickness of the moisture film and the control voltage.