There are many reasons for a black tongue. If there are no uncomfortable symptoms, it may be caused by eating dark-colored foods such as blackberry, dark chocolate, black rice porridge, or drinking dark-colored beverages such as coffee and strong tea, which can generally be relieved by rinsing the mouth with water or brushing the teeth, without special treatment. However, it may also be caused by the influence of drugs, or the patient has Yin cold, internal heat, gastrointestinal dryness and other problems. 1, drug influence: If you take a drug with a black sugar coating, when the sugar coating dissolves in the mouth, the decomposition can be attached to the tongue, which in turn will appear the performance of the tongue black; 2, Yin cold: Patients with Yin cold often have the performance of a black tongue, and moist with more fluid, and also often accompanied by The patient’s tongue is often black and moist with a lot of fluid, and often accompanied by cold extremities, cold abdomen, abdominal pain and other uncomfortable symptoms; 3, internal heat: the patient’s tongue is black with internal heat, mostly from a yellow, greasy tongue, and can also be accompanied by sticky stools, dry heat, general weakness and other uncomfortable manifestations; 4, gastrointestinal dry heat: the black tongue may also be caused by the long-term accumulation of damp and cloudy food in the stomach and intestines, which gradually floats to the tongue. Patients may also have dry stools, red and yellow urine, sore throat and other manifestations. In addition, from the Western medical point of view, the black tongue may also be caused by a black hairy tongue, mainly related to bad oral habits, prolonged smoking, abuse of broad-spectrum antibiotics, a large amount of food containing pigments and other factors, resulting in the blackening of the filiform papillae on the tongue. Patients usually have no other discomfort, and occasionally have bad breath, nausea, and itching sensation. If the darkening of the tongue is also accompanied by darkening of the lips of the mouth and nail bed, as well as dizziness, weakness, palpitations, and dyspnea, it may be the color exhibited by cyanosis due to hypoxia, mainly due to the darker color of deoxygenated hemoglobin. However, no matter which cause it is, if it is accompanied by obvious discomfort, it should be promptly treated by medical evidence to avoid delaying the condition.