Dry mouth in the middle of the night may be caused by environmental factors, nasal diseases, dry syndrome and diabetes. 1. Environmental factors: the external environment may be dry, resulting in rapid loss of body water, thus resulting in dry mouth in the middle of the night. 2. Nasal diseases: Nasal diseases can lead to nasal congestion, resulting in open-mouth breathing and dry mouth in the middle of the night, such as nasal polyps, deviated septum and so on. 3. Dry Syndrome: This disease usually causes chronic inflammation of the glands in the body, which manifests itself as dry mouth and dry eyes. 4. Diabetes mellitus: diabetic patients with poor glycemic control and high blood sugar for a long period of time will also experience dry mouth symptoms. If patients with severe or persistent symptoms of dry mouth in the middle of the night, after excluding environmental factors, should go to the hospital in time, under the guidance of a professional physician to clarify the cause of the disease.