A dispenser for dispensing a fluid contained in a bottle, made of plastic material, comprising: - a ring nut which can be screwed on the neck of a bottle and having an orifice for sucking fluid from the bottle, a series of holes positioned around the orifice and an inner cylindrical wall equipped with partial grooves; - a concertina-like deformable element, defining a return spring of the dispenser, comprising a lower cylindrical projection equipped with relative partial grooves and a dome-shaped element which rests on the orifice of the ring nut, and side walls defining a dosing chamber of the dispenser, the dome-shaped element constituting an inlet valve for the product and being designed to rise in the case of negative pressures of the dosing chamber, the concertina-like deformable element also comprising an upper portion equipped with a sealing lip designed to open in the case of a pressure of the dosing chamber greater than a predetermined threshold value; - a ring located on the ring nut and designed to define with the ring nut a locking system designed to define a configuration of use and a non-operating configuration of the dispenser by means of a reciprocal rotation of the ring and the ring nut, the ring also being hooked to the upper portion of the concertina-like deformable element in such a way as to form, by means of the sealing lip and suitable openings of the ring, an outlet valve of the dispenser and in such a way as to pull the concertina-like deformable element during the reciprocal rotation; - a dispensing head, which can be pressed by a user when the dispenser is in the configuration of use, operatively connected to the ring and equipped with a channel designed to collect the product at the outlet from the dosing chamber of the concertina-like deformable element through the openings of the ring in such a way as to dispense it through an outlet channel; - wherein the reciprocal rotation of the ring and the ring nut makes it possible to align the partial grooves of the cylindrical wall of the ring nut and the partial grooves of the concertina-like deformable element when the dispenser is in the configuration of use, so that the partial grooves (5a, 7b) form, together with the series of holes, a channel for passage of the compensation air which is distinct and separate from the conduit for dispensing the product formed by the orifice, from the dosing chamber and from the channels and of the dispensing head. - a ring nut which can be screwed on the neck of a bottle and having an orifice for sucking fluid from the bottle, a series of holes positioned around the orifice and an inner cylindrical wall equipped with partial grooves; - a concertina-like deformable element, defining a return spring of the dispenser, comprising a lower cylindrical projection equipped with relative partial grooves and a dome-shaped element which rests on the orifice of the ring nut, and side walls defining a dosing chamber of the dispenser, the dome-shaped element constituting an inlet valve for the product and being designed to rise in the case of negative pressures of the dosing chamber, the concertina-like deformable element also comprising an upper portion equipped with a sealing lip designed to open in the case of a pressure of the dosing chamber greater than a predetermined threshold value; - a ring located on the ring nut and designed to define with the ring nut a locking system designed to define a configuration of use and a non-operating configuration of the dispenser by means of a reciprocal rotation of the ring and the ring nut, the ring also being hooked to the upper portion of the concertina-like deformable element in such a way as to form, by means of the sealing lip and suitable openings of the ring, an outlet valve of the dispenser and in such a way as to pull the concertina-like deformable element during the reciprocal rotation; - a dispensing head, which can be pressed by a user when the dispenser is in the configuration of use, operatively connected to the ring and equipped with a channel designed to collect the product at the outlet from the dosing chamber of the concertina-like deformable element through the openings of the ring in such a way as to dispense it through an outlet channel; - wherein the reciprocal rotation of the ring and the ring nut makes it possible to align the partial grooves of the cylindrical wall of the ring nut and the partial grooves of the concertina-like deformable element when the dispenser is in the configuration of use, so that the partial grooves (5a, 7b) form, together with the series of holes, a channel for passage of the compensation air which is distinct and separate from the conduit for dispensing the product formed by the orifice, from the dosing chamber and from the channels and of the dispensing head.