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 a cylindrical element suitably shaped internally and defining a conduit for sucking fluid from said bottle, a series of holes positioned around said conduit and an inner cylindrical wall equipped with partial grooves; said cylindrical element comprising a neck; - a concertina-like deformable element, defining a return spring of said dispenser, comprising a cylindrical lower projection equipped with relative partial grooves, and side walls defining a dosing chamber of said dispenser, - a ring positioned on said ring nut and designed to define with the ring nut a locking system, by means of a reciprocal rotation of said ring and of said ring nut, designed to define an operating configuration and a non-operating configuration of said dispenser; said ring also being hooked to an upper portion of said concertina-like deformable element in such a way as to pull said concertina-like deformable element during said reciprocal rotation in such a way that, in said operating configuration, said partial grooves of said ring nut are aligned and said partial grooves of said concertina-like deformable element so that said partial grooves (5a, 7b) form, together with said series of holes, a channel for the passage of the compensation air; - a dispensing head, which can be pressed by a user when said dispenser is in said operating configuration, operatively connected to said ring and equipped with a collection chamber designed to collect the fluid flowing out from the dosing chamber of said concertina-like deformable element through a central opening of said ring in such a way as to dispense it through an outlet channel; said collection chamber and said dosing chamber communicating through said central opening of said ring; - a first shutoff element configured to be positioned resting on said neck and to rise in the case of negative pressures of said dosing chamber in such a way as to form together with said neck a check valve entering said dosing chamber; - a second shutoff element integral with said dispensing head and housed movably in said central opening of the ring in such a way as to define a delivery valve between said dosing chamber and said collection chamber, characterised in that it comprises a sleeve element, coaxial with said cylindrical element, interfering, at least in a supply configuration before a first pressing of the dispensing head, with at least one of said first and second shutoff elements (20, 21) in such a way as to block at least one of said first and second shutoff elements (20, 21) in a fixed position which allows said conduit and/or said central opening to be stably occluded. - a ring nut which can be screwed on the neck of a bottle and having a cylindrical element suitably shaped internally and defining a conduit for sucking fluid from said bottle, a series of holes positioned around said conduit and an inner cylindrical wall equipped with partial grooves; said cylindrical element comprising a neck; - a concertina-like deformable element, defining a return spring of said dispenser, comprising a cylindrical lower projection equipped with relative partial grooves, and side walls defining a dosing chamber of said dispenser, - a ring positioned on said ring nut and designed to define with the ring nut a locking system, by means of a reciprocal rotation of said ring and of said ring nut, designed to define an operating configuration and a non-operating configuration of said dispenser; said ring also being hooked to an upper portion of said concertina-like deformable element in such a way as to pull said concertina-like deformable element during said reciprocal rotation in such a way that, in said operating configuration, said partial grooves of said ring nut are aligned and said partial grooves of said concertina-like deformable element so that said partial grooves (5a, 7b) form, together with said series of holes, a channel for the passage of the compensation air; - a dispensing head, which can be pressed by a user when said dispenser is in said operating configuration, operatively connected to said ring and equipped with a collection chamber designed to collect the fluid flowing out from the dosing chamber of said concertina-like deformable element through a central opening of said ring in such a way as to dispense it through an outlet channel; said collection chamber and said dosing chamber communicating through said central opening of said ring; - a first shutoff element configured to be positioned resting on said neck and to rise in the case of negative pressures of said dosing chamber in such a way as to form together with said neck a check valve entering said dosing chamber; - a second shutoff element integral with said dispensing head and housed movably in said central opening of the ring in such a way as to define a delivery valve between said dosing chamber and said collection chamber,