Dry tongue and bad breath can be caused by upper respiratory tract infections, it can also be caused by diabetes, and it can also be caused by burning mouth syndrome. 1. Upper respiratory tract infection: Upper respiratory tract infection can lead to the patient’s oropharyngeal mucosal congestion and edema, which can lead to the symptoms of dry tongue and dry mouth, in addition, if the upper respiratory tract infection is caused by bacterial infections, it will lead to the human body oropharyngeal bacterial increase, so the patients with upper respiratory tract infections can appear dry tongue and bad breath symptoms. 2. Diabetes mellitus: patients with diabetes mellitus have increased urination due to increased urinary glucose, so the symptoms of dry tongue and bad breath can occur. In addition, patients with diabetes mellitus have decreased immunity, and the bacteria in the mouth and other parts of the body multiply, which can lead to the symptoms of bad breath, therefore, patients with diabetes mellitus can have dry tongue and bad breath. 3. Burning Mouth Syndrome: Burning Mouth Syndrome is a syndrome caused by various reasons with burning pain in the tongue as the main manifestation, and patients suffering from Burning Mouth Syndrome may also have symptoms of dry tongue and bad breath. In addition to the above diseases, other causes may also lead to the symptoms of dry tongue and bad breath. If these symptoms persist, you should consult a doctor to find out the cause and treat it.