During operation of a capacitive proximity sensor (1) that is provided with at least two measuring electrodes (2, 3), a first capacitance measurement variable (K1) and a second capacitance measurement variable (K2) are detected, wherein the first capacitance measurement variable (K1) is correlated with the capacitance of at least one of the measuring electrodes (2) to earth (M), while the second capacitance measurement variable (K2) is correlated with the capacitance between at least one of the measuring electrodes (2) and at least one further measuring electrode (3). A change in the first capacitance measurement variable (K1) is evaluated together with a synchronous signal profile of the second capacitance measurement variable (K2) in order to distinguish a proximity of a conductor coupled electrically to earth from the proximity of dielectric matter. In this manner, a body part passing into the detection space (11) of the proximity sensor (1) can be distinguished effectively from other substances and objects, particularly water.