There are physiological and pathological reasons for dry mouth. Physiological reasons can be found in the lack of water caused by low water intake and excessive labor intensity, and also in the dryness of the mouth caused by opening the mouth when sleeping. If the mouth is dry for a long time, without the above reasons, it is necessary to check whether there are endocrine system diseases. The common ones are diabetes mellitus, which can be characterized by dry mouth, excessive drinking, excessive urination, and excessive eating, and elevated blood glucose can be found when checking blood glucose. It can also be seen in hyperthyroidism. Due to the patient’s high metabolism, dry mouth can occur, along with irritability, increased stool frequency, and increased food intake, and thyroid hormone tests can reveal abnormalities. It can also be seen in patients with uremia, where problems with antidiuretic hormones secreted by the hypothalamus and pituitary gland lead to excessive drinking and urination, which can be detected by checking the urine specific gravity. It can also be seen in autoimmune diseases, such as dryness syndrome. When dry mouth occurs, the primary disease should be checked and treated for the primary disease.