There is a possibility of recovery from open mouth breathing for more than a decade. Open mouth breathing can be caused by inadequate oxygen supply when using nasal breathing alone and is a sign of hypoventilation. Usually, open-mouth breathing can also be recovered after improving ventilation deficiency. Open-mouth breathing is mostly found in obese patients. Obese patients have a large amount of fat accumulation around the thorax, which restricts respiratory movements and leads to narrow and blocked upper airways, requiring open-mouth breathing to increase the oxygen supply. In addition, patients with rhinitis have restricted smoothness of the airway when breathing and need to breathe through the mouth to supplement oxygen supply; patients with long-term obstructive pulmonary disease have reduced effective breathing area of the lungs and oxygen cannot enter the blood smoothly, resulting in lack of oxygen in human tissues, and need to breathe through the mouth to increase more oxygen supply; a few patients can also be caused by thoracic deformity. It is recommended that obese patients should actively reduce weight; patients with rhinitis should control inflammation; patients with obstructive lung disease should undergo long-term oxygen therapy; patients with thoracic deformity should undergo corrective surgery to relieve the symptoms of open-mouth breathing.