A method for monitoring a nozzle mouthpiece (106, 206, 306, 1006) with regard to deposits on a nozzle (101, 201, 301, 401, 501, 601, 701, 801, 901, 1001) for spraying substances, in particular dispersions, emulsions or suspensions, comprising - a nozzle body (104, 304) which has a nozzle mouthpiece (106, 206, 306, 1006), - wherein the nozzle body (104, 304) comprises an inner pipe (102, 202, 302, 402, 802, 902, 1002), said inner pipe being connected to a feed for the substance to be sprayed and comprising an inner wall and an exit opening (107, 207, 307, 807, 1007), and an outer pipe (103, 203, 303, 503, 603, 703, 803, 903, 1003), said outer pipe being distanced to the inner pipe (102, 202, 302, 402, 802, 902, 1002), being connected to a feed for a gas and comprising an exit opening (109, 209, 309, 809, 909, 1009), and - the exit opening (107, 207, 307, 807, 1007) of the inner pipe (102, 202, 302, 402, 802, 902, 1002) and the exit opening (109, 209, 309, 809, 909, 1009) of the outer pipe (103, 203, 303, 503, 603, 703, 803, 903, 1003) are arranged in the region of the nozzle mouthpiece (106, 206, 306, 1006), characterised in that an inlay (113, 213, 313, 413, 513, 613, 713, 813, 913, 1013) is arranged on the inner pipe (102, 202, 302, 402, 802, 902, 1002) or on the outer pipe (103, 203, 303, 503, 603, 703, 803, 903, 1003), wherein the inlay (113, 213, 313, 413, 513, 613, 713, 813, 913, 1013) is arranged such that it can be brought or is brought into oscillation by way of the substance to be sprayed which exits out of the exit opening (107, 207, 307, 807, 1007) of the inner pipe (102, 202, 302, 402, 802, 902, 1002) and/or by way of the gas which flows out of the exit opening (109, 209, 309, 809, 909, 1009) of the outer pipe (103, 203, 303, 503, 603, 703, 803, 903, 1003), in order to minimise or prevent deposits in the exit region (112, 212, 312, 412, 512, 612, 712, 812, 912, 1012) of the substance to be sprayed and/or of the gas, wherein a sensor which is connected to a control unit monitors the nozzle mouthpiece (106, 206, 306, 1006) with regard to deposits and transmits signals to the control unit and given a deposition in the exit region (112, 212, 312, 412, 512, 612, 712, 812, 912, 1012) of the substance to be sprayed and/or of the gas, said deposition being determined by the sensor, the control unit transmits a signal to a device. - a nozzle body (104, 304) which has a nozzle mouthpiece (106, 206, 306, 1006), - wherein the nozzle body (104, 304) comprises an inner pipe (102, 202, 302, 402, 802, 902, 1002), said inner pipe being connected to a feed for the substance to be sprayed and comprising an inner wall and an exit opening (107, 207, 307, 807, 1007), and an outer pipe (103, 203, 303, 503, 603, 703, 803, 903, 1003), said outer pipe being distanced to the inner pipe (102, 202, 302, 402, 802, 902, 1002), being connected to a feed for a gas and comprising an exit opening (109, 209, 309, 809, 909, 1009), and - the exit opening (107, 207, 307, 807, 1007) of the inner pipe (102, 202, 302, 402, 802, 902, 1002) and the exit opening (109, 209, 309, 809, 909, 1009) of the outer pipe (103, 203, 303, 503, 603, 703, 803, 903, 1003) are arranged in the region of the nozzle mouthpiece (106, 206, 306, 1006),