Tongue diagnosis dates to the Shang Dynasty which began c.1600 B.C. and ended c.1000. Throughout the time since it has evolved into a very important tool of diagnosis.
The tongue is considered to be an exterior part of the body because it's in almost contact with the air - the exterior. This is certainly different from the American view but extremely productive. An acupuncturist or herbalist will, in the mind’s eye, overlay a tongue with several different maps. Each map is shaped by the diagnostic model or system which it represents.
The diagram on the left represents the internal organs. The center diagram represents the body as having three parts - upper burner, middle burner, and lower burner. The diagram on the right represents the body as having two parts - interior and exterior.
The practitioner examines the general and local shape, and the color of both the tongue body and coat. A healthy tongue will be pink (like a kitten or puppy’s tongue) and moist with a thin clear or white coat. Thin is defined as a coat through which the tongue body can be seen. Some signs of imbalance or pathology are red body, yellow coat, thick coat like mozzarella cheese, very dry body or cracks in the coat or body itself.