Breathing through the mouth has less heating, humidifying and filtering effect on the air from the nasal cavity, which may have adverse effects on the respiratory tract and is recommended to be corrected. Ways to change breathing through the mouth include self-training, treating nasal disorders, and eliminating other causes. 1. Self-training: If there is no other disease, and the mouth breathing is only caused by bad habits, through self-training, open-mouth breathing may be relieved after getting into the habit. 2. Treatment of nasal diseases: Breathing through the mouth in many cases is caused by nasal disorders, such as sinusitis, nasal polyps, allergic rhinitis and other related conditions, which need to be actively dealt with. (1) In the case of sinusitis or nasal polyps, surgery may be required; (2) In the case of allergic rhinitis, antihistamines such as cetirizine hydrochloride may need to be taken for treatment to improve the patient’s nasal ventilation, which will be helpful in correcting breathing through the mouth. 3. Eliminate other causes: sometimes mouth breathing may be related to obstructive sleep apnea. People with obstructive sleep apnea may involuntarily open their mouths to breathe at night during sleep due to the collapse of the upper airway. Mouth breathing may be improved or alleviated by treatment with a noninvasive ventilator at night. In summary, when the manifestation of breathing through the mouth occurs, the specific cause needs to be investigated and individualized.