The invention relates to an atomiser, in particular an inhaler, for atomising a liquid active agent to form an aerosol, having an active agent reservoir (1), an atomiser nozzle (2) and a pump arrangement (3), wherein a suction side (4) of the pump arrangement (3) leads into the active agent reservoir (1) and a pressure side (5) of the pump arrangement (3) leads into the atomiser nozzle (2), and wherein the pump arrangement (3) has a plunger (7) that can be adjusted in a cylinder (6) in the axial direction (x) of the cylinder (6), characterised in that the plunger (7) is supported in portions along its outer circumference (8) in a form-fitting manner on an inner wall (9) of the cylinder (6) and a gap (10) is formed in portions between the inner wall (9) of the cylinder (6) and the plunger (7), wherein the plunger (7) is rotatably mounted around its longitudinal axis (x) in the cylinder (6) and can be adjusted between a suction position, in which a pump chamber (11) of the pump arrangement (3) is connected to the suction side (4) via the gap (10), and a pump position, in which the plunger (7) closes the suction side (4). A corresponding method is also described.
