The dangers of sleeping and breathing with the mouth open may cause respiratory diseases, oral diseases, adenoidal facies, and affect the quality of sleep. 1. Suffer from respiratory diseases. Sleeping with the mouth open and breathing without the filtering effect of the nasal cavity on the dust and bacteria in the air, directly into the lungs, may cause laryngitis and cough. 2. Suffer from oral diseases. Prolonged open-mouth breathing may cause a large amount of water loss mitigates the cleaning effect of saliva on the oral cavity as well as the air directly to the oral mucosa stimulation, periodontal disease and tooth decay may occur. 3. Adenoid face. Children who sleep with their mouths open for a long time can cause high arches of the hard palate, hypertrophy of the upper lip, uneven upper row of teeth, and adenoid face. 4. Impact on sleep quality. Open-mouth breathing affects the quality of sleep and leads to poor concentration during the day. Sleeping with open mouth breathing is mostly caused by nasal and nasopharyngeal diseases and tonsil hypertrophy. It is recommended to consult the hospital for a clear diagnosis and treatment, and try to avoid open-mouth breathing during sleep.