Observation of the tongue, also known as tongue diagnosis, is an important procedure in diagnosis by inspection in TCM. It provides primary information for the Chinese physicians to make diagnosis.

Why is it said that the observation of the tongue can determine the pathological change of the internal organs?

The theory of TCM believes that the tongue directly or indirectly connects with many zang-fu organs through the meridians and collaterals.

The deep branch of Heart Meridian of Hand-Shaoyin goes to the root of the tongue, the Spleen Meridian of Foot-Taiyin traverses the root of the tongue and spreads over its lower surface, the Kidney Meridian of Foot-Shaoyin terminates at the root of the tongue. Therefore, the essential qi of the zang-fu organs can go upward to nourish the tongue, and pathological changes of the zang-fu organs can be reflected by changes in tongue conditions Therefore, the observation of the tongue can determine the pathological changes of the internal organs.

How to observe the tongue?

Observation of the tongue includes the tongue proper and its coating.

The tongue proper refers to the muscular tissue of the tongue, which is also known as the tongue body.

The tongue coating refers to a layer of "moss" over the tongue surface, which is produced by the stomach qi.

A normal tongue is of proper size, soft in quality, free in motion, slightly red in color and with a thin layer of white coating which is neither dry nor over moist.

The tongue is divided into four areas, namely, tip, central part, root and border. The tip of the tongue often reveals the pathological changes of the heart and lung, its border reveals those of the liver and gallbladder, its central part reveals those of the spleen and stomach, and its root reveals those of the kidney. This method of diagnosing the pathological changes of the zang-fu organs by dividing the tongue into corresponding areas is clinically significant.

1. Tongue proper

This is to observe the color and form of the tongue proper.

a) Color of the tongue proper A pale tongue is less red than a normal tongue, and indicates syndromes of deficiency type and cold syndromes caused by deficiency of yang qi or insufficiency of qi and blood.

A red tongue is bright red and redder than a normal tongue. It indicates various heat syndromes including interior heat syndromes of excess type and interior heat syndromes of deficiency type.

A deep red tongue indicates an extreme heat condition. In exogenous febrile diseases, it indicates invasion of pathogenic heat. In endogenous diseases, it indicates yin deficiency leading to hyperactivity of fire.

A blue purple tongue indicates stagnation of blood, which is related to either cold or heat. A deep blue purplish tongue, dry and lusterless, is related to heat, whilst a pale purplish and moist tongue is related to cold. The presence of purplish spots on the tongue surface also indicates stagnation of blood.

b) Form of the tongue proper

A swollen tongue is larger than normal. If a swollen tongue is delicate in quality and pale in color, and with tooth prints on the border, it indicates yang deficiency of the spleen and kidney. The condition is due to impaired circulation of body fluid producing harmful water, retained fluid, phlegm and damp. If a swollen tongue is deep red in color occupying the entire space of the mouth, it indicates excessive heat in the heart and spleen. If a swollen tongue is blue purplish and dark, it indicates toxicosis.

A thin tongue is smaller and thinner than normal. A thin and pale tongue indicates deficiency of qi and blood. A thin, dry and deep red tongue indicates hyperactivity of fire due to deficiency of yin in which body fluid is consumed.

A cracked tongue indicates excessive heat consuming body fluid if the tongue is deep red in color, and indicates deficiency of blood if the tongue is pale. A cracked tongue may be present in a normal person. If so, the cracks are not deep, and remain there all the time unchanged. This is considered normal.

A thorny and red tongue (the papillary buds over the surface of the tongue swell up like thorns) indicates accumulation of pathogenic heat in the interior. The more the pathogenic heat is, the more enlarged and profuse the thorns will be.

A deviated tongue indicates wind-stroke or early threatening signs of wind-stroke.

A rigid tongue lacks flexibility and is difficult to protrude, retract or roll. A rigid tongue seen in exogenous febrile diseases often indicates invasion of the pericardium by heat, retention of turbid phlegm in the interior, or excessive pathogenic heat consuming body fluid. A rigid tongue present in endogenous diseases indicates wind stroke or early threatening signs of wind-stroke.

A flaccid tongue is weak in motion and often indicates extreme deficiency of qi and blood or consumption of yin fluid depriving the tongue of the nourishment. If a flaccid tongue is pale, it indicates deficiency of qi and blood. If it is deep red, it indicates collapse of yin.

Tongue coating

a) Quality of the tongue coating

i) Thick coating and thin coating:

The tongue coating is considered thin when the tongue proper can indistinctly be seen through it, and considered thick when the tongue proper cannot be seen through it. One can understand the severity of the pathogenic factors and progression of the pathological conditions by distinguishing the thickness and thinness of the tongue coating. Generally speaking, a thin tongue coating is present when the superficial portion of the body is affected in a disease, or when the disease is due to deficiency of the anti-pathogenic qi. Retention of damp and phlegm or food in the interior of the body, or inward transmission of the pathogenic factor from the exterior may produce a thick tongue coating. Thickening of coating indicates inward transmission of the pathogenic factor from the exterior, and is a sign of aggravation of the disease. Thinning of coating points to gradual elimination of the pathogenic factor, and is a sign of alleviation of the pathological conditions.

ii) Moist coating and dry coating: One can understand the condition of the body fluid by distinguishing the moisture and dryness of the tongue coating A normal tongue coating is moist and lustrous, which is the manifestation of normal dissemination of the body fluid. A dry tongue coating, which looks coarse and feels lacking moisture indicates consumption of body fluid due to excessive heat or consumption of yin fluid not allowing it to nourish upwards. If there is excessive moisture over the tongue surface, and the saliva dribbles when the tongue is stuck out in a severe case, it is a slippery tongue coating. The condition is due to upward flooding of harmful water and damp.

iii) Sticky coating and granular coating Both sticky and granular tongue coating help deduce the turbid damp in the intestines and stomach. It is a sticky coating when the tongue is covered by a turbid layer of fine greasy substance, which is hard to be scrubbed. A sticky tongue coating is often seen in syndromes resulting from retention of turbid damp and phlegm or retention of food. It will be a granular coating if the granules on the tongue surface are coarse, loose and thick like residue of making curd, and easily scrubbed.

iv) A pasty tongue coating often results from excessive yang heat bringing the turbid qi in the stomach upwards. It is also seen in syndromes caused by retention of turbid phlegm or retention of food.

v) Peeled Coating: The tongue with a part of its coating peeling off is known as "geographical tongue". It is a sign of consumption of qi and yin of the stomach. If the entire coating peels off leaving the surface mirror smooth, the condition is known as "glossy tongue". It is a sign of exhaustion of the stomach yin and severe damage of the stomach qi.

b) Color of the tongue coating i) White Coating A thin and white coating is normal. Yet a white coating may appear in an illness. If so, it indicates exterior syndromes and cold syndromes. A thin and white coating is present in exterior cold syndromes, whilst a thick and white coating is seen in interior cold syndromes.

ii) Yellow coating A yellow coating indicates interior syndromes and heat syndromes. The deeper yellow the coating refers to the more severe pathogenic heat it indicates. A light yellow coating points to mild heat, a deep yellow coating to severe heat, a burnt yellow coating to accumulation of heat.

iii) Grey coating: Gray coating indicates interior syndromes, and may be seen in interior heat syndromes or syndromes resulting from cold and damp. If a grey coating is yellowish and dry, it signifies consumption of body fluid due to excessive heat. If a grey coating is whitish and moist, it implies retention of cold damp in the interior or retention of phlegm and fluid. As a grey coating often develops into a black coating, a greyish black coating is seen

iv) Black coating: A black coating indicates interior syndromes due to extreme heat or excessive cold. A black coating is often the outcome of the further development of a yellow coating or a grey coating, It is present at the severe stage of an illness. If a black coating is yellowish and dry, possibly with thorns, it signifies consumption of body fluid due to extreme heat. A pale black and slippery coating implies excessive cold due to yang deficiency.

4. Precautions in tongue diagnosis

As each disease undergoes a complicated process, the conditions of the tongue proper and its coating are the manifestations of interior complicated pathological changes. The conditions of the tongue proper mainly reflect deficiency or excess of the zang-fu organs and relative strength of the essential qi. The condition of the tongue coating reflects the depth and nature of the invading pathogenic factors.

A comprehensive analysis of the conditions of both the tongue proper and its coating is required on the basis of their respective indications. The condition of the tongue proper and that of its coating are generally conformable; the disease to be indicated is often the outcome of combining the two.

For instance, retention of heat of excess type in the interior produces a red tongue with a dry and yellow coating; a pale tongue with a moist and white coating is often present in cold syndromes of deficiency type. But situations, in which the condition of the tongue proper does not agree with the condition of its coating, may occur. Only by a comprehensive analysis can reliable information be provided for further differentiation of syndromes.

It is desirable to observe the tongue in direct natural light. The patient is required to protrude the tongue naturally.

Some food and drugs may color the tongue coating, and the thickness and moisture of the tongue coating may change after eating or scraping the tongue. Attention should be paid to the exclusion of false phenomena induced by such factors in the clinical situation.