Why yellow tongue?

Normal tongue picture should be bright red color, moist tongue quality, moderate size, soft and flexible, uniform thin white and moist tongue coating, indicating that stomach qi is exuberant, qi, blood and body fluid are abundant, and the function of viscera is normal. If the tongue coating is yellow, it can be divided into yellow, dark yellow and scorched yellow according to the degree of yellow coating. Yellow coating can also be divided into interior syndrome and heat syndrome. Due to the burning of heat pathogen, the tongue coating is yellow. Light yellow coating indicates light heat potential, which is more common in external wind-heat syndrome or wind-cold heat syndrome. The moss is yellow and rich in fluid, which is mostly seen in the body with yang deficiency and cold dampness. Phlegm accumulation for a long time turns heat, or deficiency of qi and blood, and damp-heat pathogen; the moss is yellow and dry, even dry, which is mostly seen in the syndrome of pathogenic heat damaging fluid, dryness and excess of viscera; the moss is yellow and greasy, which is mostly seen in damp-heat or phlegm heat accumulation, or food accumulation and decay.