Mask for underwater use, comprising: a frame; a transparent part supported by the frame; a gasket part mounted on the frame and designed to be positioned on the face of a user, the gasket part comprising: - a partitioning wall designed to rest on the user's nose when the mask is worn so as to form an upper chamber and a lower chamber sealingly separated from each other and with the lower chamber accommodating the user's nose and mouth, wherein the two chambers are connected through a passage provided in the partitioning wall and at least one inner one-way valve so that air can pass from the upper chamber to the lower chamber but not vice versa; - a perimeter edge designed to rest on the perimeter of the user's face to laterally delimit said upper chamber and said lower chamber, - a snorkel comprising at least one first and one second channel (104, 204) which connect the upper chamber and the lower chamber, respectively, with the external environment, - at least one discharge duct arranged on the perimeter edge of the gasket to convey the exhaled air into the second channel of said snorkel, the exhaled air being conveyed into said snorkel by means of a pair of small discharge ducts arranged on the perimeter edge and adjacent thereto, characterized in that the perimeter edge of the gasket comprises one single discharge opening which is located at the region adapted to be arranged near the user's mouth and which is the seat of a valve-like non-return mechanism, the valve-like non-return mechanism comprising at least one valve seat and a valve applied to the said discharge opening while the mask further comprises a lower connection element arranged in the lower part of the perimeter edge of the gasket near said discharge opening so as to connect said discharge opening with said at least one discharge duct conveying therein the exhaled gases running from the outer valve. a frame; a transparent part supported by the frame; a gasket part mounted on the frame and designed to be positioned on the face of a user, the gasket part comprising: - a partitioning wall designed to rest on the user's nose when the mask is worn so as to form an upper chamber and a lower chamber sealingly separated from each other and with the lower chamber accommodating the user's nose and mouth, wherein the two chambers are connected through a passage provided in the partitioning wall and at least one inner one-way valve so that air can pass from the upper chamber to the lower chamber but not vice versa; - a perimeter edge designed to rest on the perimeter of the user's face to laterally delimit said upper chamber and said lower chamber, - a snorkel comprising at least one first and one second channel (104, 204) which connect the upper chamber and the lower chamber, respectively, with the external environment, - at least one discharge duct arranged on the perimeter edge of the gasket to convey the exhaled air into the second channel of said snorkel, the exhaled air being conveyed into said snorkel by means of a pair of small discharge ducts arranged on the perimeter edge and adjacent thereto, - a partitioning wall designed to rest on the user's nose when the mask is worn so as to form an upper chamber and a lower chamber sealingly separated from each other and with the lower chamber accommodating the user's nose and mouth, wherein the two chambers are connected through a passage provided in the partitioning wall and at least one inner one-way valve so that air can pass from the upper chamber to the lower chamber but not vice versa; - a perimeter edge designed to rest on the perimeter of the user's face to laterally delimit said upper chamber and said lower chamber, - a snorkel comprising at least one first and one second channel (104, 204) which connect the upper chamber and the lower chamber, respectively, with the external environment, - at least one discharge duct arranged on the perimeter edge of the gasket to convey the exhaled air into the second channel of said snorkel, the exhaled air being conveyed into said snorkel by means of a pair of small discharge ducts arranged on the perimeter edge and adjacent thereto, characterized in that the perimeter edge of the gasket comprises one single discharge opening which is located at the region adapted to be arranged near the user's mouth and which is the seat of a valve-like non-return mechanism, the valve-like non-return mechanism comprising at least one valve seat and a valve applied to the said discharge opening while the mask further comprises a lower connection element arranged in the lower part of the perimeter edge of the gasket near said discharge opening so as to connect said discharge opening with said at least one discharge duct conveying therein the exhaled gases running from the outer valve.