Dry mouth can be the result of a dry environment, upper respiratory infection, diabetes, hyperthyroidism, dry syndrome, uremia, and gastroesophageal reflux disease. 1. Environmental dryness: long-term in a hot and hot environment, the air is dry and lack of circulation, the body water loss with sweat, so the mouth will be dry. In addition, drinking too little water, diarrhea and other factors can also cause dry mouth. 2. Upper respiratory tract infection: viral infection of the body as an exogenous pyrogen, inducing the hypothalamus to upregulate body temperature regulation point, the body through a series of ways to increase heat production, resulting in an increase in body temperature, so it will be dry mouth. 3. Diabetes: diabetic patients with elevated urine osmolality, osmotic diuresis, resulting in a large amount of water in the body into the urine discharge, so the mouth will be dry. 4. Hyperthyroidism: hyperthyroidism increases the synthesis and secretion of thyroid hormones, the body’s cellular metabolism, increased heat production and dry mouth. 5. Dry syndrome: immune system dysfunction leads to salivary glands being attacked by autoantibodies, saliva synthesis and secretion is insufficient and dry mouth. 6. Uremia: dry mouth due to decreased level of antidiuretic hormone or decreased sensitivity to its action, resulting in large amounts of urine formation. 7. Gastroesophageal reflux disease (GERD): stomach acid and other gastric content in the lower esophageal sphincter dysfunction reflux into the oral cavity, so the mouth will be dry. Dry mouth may be related to a variety of factors, serious cases are recommended to consult a doctor for a clear diagnosis, follow the doctor’s instructions for standardized treatment.