Sleeping with open mouth in adults may be due to various diseases of the nasopharyngeal cavity, short upper lip, difficulty in closing the lips, etc. Treat the respiratory diseases accordingly and instruct the patient to perform lip muscle training. 1. If an adult’s mouth is open during sleep due to nasopharyngeal disorders such as sinusitis, rhinitis, nasal polyps, enlarged turbinates, enlarged pharyngeal tonsils, etc., the patient should consult an ENT or respiratory physician for treatment of possible respiratory disorders. 2. If an adult’s mouth is open during sleep because the upper lip is too short and it is difficult to close the lip, the doctor should instruct the patient to carry out lip muscle training. Adults with open mouth in their sleep are advised to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.