A device for improving breathing, comprising: a mouth cover comprising an annular member defining a central open region therethrough and including a first surface comprising adhesive thereon for detachably attaching the mouth cover to skin of a user surrounding the user's mouth; and a lip closing element comprising an elastic membrane attached to a second surface of the mouth cover opposite the first surface and extending across the central open region and including one or more openings therethrough; characterized by a flap positioned between the mouth cover and lip closing element and secured therebetween, the flap movable towards the lip closing element to close the openings, and away from the lip closing element, to allow airflow through the openings; wherein said flap is formed from relatively thin, strong, flexible material such that when a user separates his lips, the flap may still initially cover the openings in the lip closing element so that a positive pressure across the adhesive device due to a relatively higher pressure inside the user's mouth than outside causes the flap to press against the lip closing element, sealing the openings, enabling the user to inhale to generate a negative pressure, thereby directing the flap away from the lip closing element and allowing the user to inhale through the openings, wherein sufficient elasticity of the lip closing element and mouth cover enables the user to open their lips further until the flap no longer covers the openings enabling the user to inhale and exhale; and when the user relaxes their lips and/or mouth, the lip closing element may resiliently close or return towards the relaxed configuration, thereby covering the openings once again with the flap. a mouth cover comprising an annular member defining a central open region therethrough and including a first surface comprising adhesive thereon for detachably attaching the mouth cover to skin of a user surrounding the user's mouth; and a lip closing element comprising an elastic membrane attached to a second surface of the mouth cover opposite the first surface and extending across the central open region and including one or more openings therethrough; characterized by a flap positioned between the mouth cover and lip closing element and secured therebetween, the flap movable towards the lip closing element to close the openings, and away from the lip closing element, to allow airflow through the openings; wherein said flap is formed from relatively thin, strong, flexible material such that when a user separates his lips, the flap may still initially cover the openings in the lip closing element so that a positive pressure across the adhesive device due to a relatively higher pressure inside the user's mouth than outside causes the flap to press against the lip closing element, sealing the openings, enabling the user to inhale to generate a negative pressure, thereby directing the flap away from the lip closing element and allowing the user to inhale through the openings, wherein sufficient elasticity of the lip closing element and mouth cover enables the user to open their lips further until the flap no longer covers the openings enabling the user to inhale and exhale; and when the user relaxes their lips and/or mouth, the lip closing element may resiliently close or return towards the relaxed configuration, thereby covering the openings once again with the flap.