Sleeping with a dry and bitter mouth may be physiological factors, but also may be the manifestation of certain diseases, such as oral diseases, respiratory diseases, digestive diseases, autoimmune diseases, etc., should be timely to find out the cause of the disease. 1. Physiological factors: If the rest environment is dry or in the fall, winter and other dry seasons, coupled with less drinking water, can also lead to the symptoms of bitter, dry and astringent mouth in the morning. 2. Pathologic factors: (1) Oral disease: when the oral cavity is not cleaned properly, bacterial infection may occur, and in the long run, a chronic inflammatory response may be formed, causing gingivitis, dental calculus, dental caries, oral ulcers and other oral diseases, which can also lead to bitter, dry and astringent mouth in the morning, and sometimes accompanied by pain and swelling and the corresponding clinical discomforts. (2) Respiratory diseases: when there are rhinitis, bronchial inflammation, upper respiratory tract infections and other diseases, can lead to nasal congestion, patients are forced to open their mouths to breathe, which causes bitter, dry and astringent mouth in the morning. (3) Digestive system diseases: such as gastritis, esophagitis, cholecystitis, cirrhosis and other diseases, these diseases are prone to gastric acid reflux or bile excretion is not normal, which can cause bitter, dry and astringent mouth in the morning. (4) autoimmune diseases: such as dry syndrome, this disease can lead to salivary glands, lacrimal gland involvement, often manifested as dryness in all parts of the body, and the involvement of the oral cavity will lead to bitter mouth in the morning, dry mouth, astringent, and sometimes may induce ulcers. If physiological causes are ruled out, the patient should consult a doctor to clarify the cause of the disease and undergo appropriate examinations if necessary.