The darkening of the tongue is considered in Chinese medicine to be mainly due to two things: First, kidney deficiency, which results in black moss. Secondly, in people with chronic fever, the patient’s heat extremes turn into fire, and the fire burns the tongue, forming black moss. In modern medicine, it is believed that black tongue moss is the appearance of various bacteria, mold and other microorganisms on the top of the tongue, which appear sick and can also grow like crazy, especially mold, and it will appear that the tongue moss turns black or brown. If the condition improves, the tongue will return to normal, and the black moss also suggests that the body’s immune system is declining very seriously.