What's wrong with black tongue?

Tongue diagnosis is to observe the changes in the patient's tongue and tongue coating, to diagnose the disease method, is an important part of the inspection, normal tongue coating is thin white coating. There are many reasons for the blackening of the tongue coating in children, taking certain antibiotics for a long time can produce black coating. A variety of black brown foods can also dye the tongue coating gray black, such as: olive, sour plum, mulberry, chocolate, etc., the black coating caused by the above situation can generally fade on its own. The black fur caused by the above reasons is caused by diseases, and the specific manifestations are as follows: gray-black fur and wet, mostly caused by yang deficiency, cold and dampness, or phlegm retention; gray-black fur and dry, mostly caused by heat and extreme body injury; yellow-black fur, mostly seen in gastrointestinal dampness, accumulated heat, or damp-heat phlegm.