There are many causes of dry mouth. First of all, dry mouth may be caused by diabetes, diabetes will cause the human body to drink more, urinate more, due to the rapid loss of water in the body, often cause the human body to appear dry mouth. Secondly, it may be caused by hyperthyroidism. Hyperthyroidism will cause the body’s basal metabolism to be too fast, sympathetic excitement, increased heat production and accelerated heat dissipation, which will cause dry mouth, thirst, excessive sweating, irritability and dry skin. In addition, dry mouth may be caused by dry syndrome, which is an immune disease of human body. If it is not detected and treated early, it often shows dry mouth, itchy skin, thirst and bad breath.