There is a possibility of recovery from open-mouth breathing for more than a decade. Open-mouth breathing is primarily a sign of inadequate ventilation due to insufficient oxygen supply when breathing solely through the nose. Usually the open-mouth breathing can also be recovered after improving the hypoventilation situation. The formation of open-mouth breathing can be caused by obesity. In obese patients, there is a large accumulation of fat around the thorax, which restricts respiratory movements and thus leads to narrowing and blockage of the upper airway, requiring open-mouth breathing to increase the oxygen supply. In patients with rhinitis, the smoothness of the respiratory tract is restricted when breathing, and they also need to breathe through the mouth to supplement the oxygen supply. In patients with long-term obstructive pulmonary disease, the effective breathing area of the lungs is reduced and oxygen cannot enter the bloodstream smoothly, resulting in oxygen deficiency in human tissues, which needs to be improved by increasing more oxygen supply through open-mouth breathing. Very few patients are caused by thoracic deformity. Different measures should be taken for different causes. Obese patients should actively reduce weight; patients with rhinitis should control inflammation; patients with obstructive lung disease should have long-term oxygen therapy to relieve hypoxia; and patients with thoracic deformity should undergo corrective surgery. Through the above treatments, patients with improved ventilation can generally open mouth breathing can be gradually relieved.