Bitter and dry mouth may be a sign of diabetes, reflux esophagitis, dry syndrome, acute pharyngitis, sleep apnea and other diseases. 1. Diabetes mellitus: prolonged hyperglycemia leads to an increase in glucose content in the urine, which in turn leads to osmotic diuresis and loss of water in the body with the urine, so the mouth will be bitter, dry mouth, polyuria, and accompanied by varying degrees of weight loss. 2. Reflux esophagitis: because of the lower esophageal sphincter dysfunction, esophageal mucosal barrier function and other factors lead to gastric acid reflux through the esophagus, into the oral cavity after the residual in the oral cavity, and thus will be bitter mouth, dry mouth, accompanied by heartburn, belching (hiccups), loss of appetite and other symptoms. 3. Dry syndrome: salivary glands are attacked by autoimmune disease, resulting in salivary secretion disorders, the mouth for a long time lack of saliva and bitter dry mouth. 4. Acute pharyngitis: Bacteria, viruses and other pathogens infecting the pharynx lead to an acute inflammatory reaction of the mucous membrane, resulting in edema and bleeding of the pharynx, accompanied by fever, and therefore a bitter and dry mouth. 5. Sleep apnea: As a result of prolonged breathing at night with the mouth open, leading to moisture in the mouth dry, so the mouth will be bitter and dry. Bitter and dry mouth may be related to many factors, it is recommended to consult a doctor for a clear diagnosis.