Waking up in the morning with a black tongue may be due to gastrointestinal disorders, fungal infections, infectious diseases, dietary factors and other reasons. 1. Gastrointestinal dysfunction: It is the gastrointestinal dysfunction caused by physiological, psychological, social, disease and other factors, which is mainly manifested as acid reflux, nausea, vomiting and other conditions. At the same time, when the gastrointestinal dysfunction, it may cause dysfunction of the flora on the tongue, which will lead to the blackening of the tongue. 2. Fungal infections: they can also cause dysfunction of the flora on the tongue, which can lead to the blackening of the tongue. 3. Infectious diseases: such as pneumonia, peritonitis, cholecystitis, etc., which cause imbalance of the immune system in the body, and bacteria or viruses multiply on the tongue, resulting in the blackening of the tongue. 4. Dietary factors: it is due to the consumption of melanin food, thus coloring the tongue. It should be noted that, no matter which cause, if the tongue turns black, you should go to the regular hospital for timely treatment.