Yellow tongue in the morning may be caused by hyperpigmentation, bacterial infection and flora disorders. 1. Hyperpigmentation: If the patient has eaten some yellow foods, drinks and medicines, etc., the yellow pigment will be deposited on the surface of the tongue, and the yellowing of the tongue will occur. 2. Bacterial infection: If the patient’s tongue has bacterial or fungal infections, such as inflammation of the tongue, hairy tongue, etc., it may also cause the tongue to appear yellowish phenomenon. 3. Flora disorders: In addition, if the patient has gastrointestinal dysfunction, which leads to the patient is prone to intra-oral flora disorders, and then cause the patient to appear the symptoms of yellowing of the tongue. Therefore, it is recommended that the patient go to the hospital for examination in time, after clarifying the cause of the disease, to carry out targeted treatment.