Black tongue is not common in the clinic, there are many reasons, as follows: 1, exogenous pigment: such as the consumption of black food, especially mulberry, drinking Chinese medicine soup can lead to a black tongue, the treatment of gastric disease drugs such as colloidal bismuth, can make the tongue staining color black, generally after drinking water, rinse easy to restore the normal appearance; 2, black hair tongue: most often in middle-aged people, the cause is unknown, may be related to local Hygiene habits, tongue papilla site pigmentation, bacterial or fungal growth, manifested as the tongue papilla hyperplasia and color blackening, generally through the strengthening of local cleaning, or the use of antibacterial drugs for treatment can be improved; 3, tongue parts of the abnormal blood circulation: local blood stagnation, sometimes the tongue appears dark, black color, Chinese medicine point of view that belongs to the body of the cold Qi overload lead.