Thirst simply means that when a person’s body lacks water, or when the mouth stays dry, he or she will be tempted to drink and feel thirsty. The three common causes of thirst are excessive water loss, prolonged low water intake and systemic diseases. The first is due to excessive water loss due to exercise, fever, vomiting, diarrhea, and so on. When a person suffers from a systemic disease, thirst can also be caused. When a person suffers from diabetes, excessive urination leads to excessive water loss, and he or she will always want to drink water. When a person is suffering from tumor, the tumor will release various hormones that cause the body’s balance to be imbalanced, thus producing a thirst response. Therefore, if you are thirsty for water, it is best to go to the hospital for relevant tests such as blood sugar and immune function tests, and then treat the original disease that causes thirst and provide rehydration treatment according to the condition.