The pump (1) has a distribution head (3) that is movable on a pump body (2) between a rest position and a product delivering position. The head has a cylinder (4) forming a dosage chamber (41), and a channel (7) assuring a passage of a liquid product or air from the chamber towards an ejection orifice (8) of a push button (18). The button is arranged on a top part of the cylinder through a skirt (14), and actuates an axial displacement of the cylinder. A sealing base is fitted in the cylinder, while the channel is fitted between an outer wall of the cylinder and an inner wall of the skirt.
