Feeling dry in the mouth is likely to be due to the lack of water in the body, which should be promptly rehydrated. If the symptoms cannot be well relieved by hydration, it means that it is caused by the decrease of saliva secretion due to the damage of salivary gland, which is mainly seen in the patients of dry mouth syndrome, mostly occurring in the female population aged 40-50. Due to the damage of salivary gland caused by immune function disorder, the salivary secretion is severely decreased, which causes the phenomenon of long-term dryness in the mouth. Patients with diabetes mellitus also suffer from dry mouth. The main symptom of diabetes mellitus is an increase in urine, which causes a decrease in body water due to an increase in urine volume, thus leading to dry mouth. Patients with hyperthyroidism will also have dry mouth. Hyperthyroidism will cause an increase in the body’s basal metabolic rate, resulting in a large amount of sweating and causing dry mouth.