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Tongue Diagnosis Content |
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1. Observe the Tongue Spirit
“Prosperity” refers to a moist, red, and vibrant tongue, indicating vitality and brightness, hence it is said to have spirit, even in illness it is a good sign. “Withering” refers to a dry and lifeless tongue, lacking vitality and luster, hence it is said to lack spirit, which is a bad sign.
2. Differentiate Tongue Color
Pale White Tongue is lighter than the normal light red color, even lacking blood color, referred to as a pale white tongue.
Indicates Deficiency Syndrome, Cold Syndrome or Dual Deficiency of Qi and Blood. If the pale white tongue is moist and the tongue body is fat and tender, it is mostly a Yang Deficiency Cold syndrome. If the pale white tongue is shiny or the tongue body is thin, it indicates Dual Deficiency of Qi and Blood.Red Tongueis deeper than the light red color, even appearing bright red, referred to as a red tongue
Indicates Heat Syndrome. If the tongue is bright red with prickles, or has a thick yellow coating, it mostly indicates Excess Heat Syndrome. If the tongue is bright red with little coating, or has cracks or is bright red without coating, it indicates Deficiency Heat Syndrome.
Dark Red Tongue is a deeper red than the red tongue, referred to as a dark red tongue.
Indicates: Excess Heat in the Interior, Yin Deficiency with Excess Fire (Heat entering the Blood Level)In cases of external pathogens, if the tongue is dark red with coating or has red spots and prickles, it indicates warm disease Heat entering the Nutritional Blood. In cases of internal injury, if the tongue is dark red with little coating or no coating, or has cracks, it indicatesChronic Illness with Yin Deficiency and Excess Fire. Additionally, if the tongue is dark red with little coating and moist, it indicatesBlood Stasis.
Purple Tongueindicates Stagnation of Qi and Blood (including Blood Stasis, Cold Heat, Extreme Heat, Poisoning…)
① Blue Purple Tongue with Thin White Coating. Indicates: Cold congealing the blood vessels, water qi rising and dampness; Yin cold with food and dampness.Diagnosis:Yang Deficiency with Water Overflowing and Blood Stasis. Commonly seen in various heart failures, pulmonary heart disease with hypoxia, etc.② Pale Red Purple Spot Tongue with Thin White Moist Coating. Indicates: Cold dampness congealing and blocking, Qi and Blood stagnation; heart and liver blood stasis.Diagnosis: Qi Stagnation in the Liver, Blood Stasis Blocking the Lung. Can be seen in lung cancer, liver cancer, liver cirrhosis, coronary heart disease, etc.③ Pale Purple with Teeth Marks Tongue and Pale Yellow Greasy Coating. Indicates: Wind cold transforming into heat; wind heat on the surface; spleen deficiency with damp heat blocking.Diagnosis:Constitutional Dampness, External Wind Cold Transforming into Heat. Can be seen in chronic nephritis with concurrent cold.Dark purple and dry with little moisture indicatesExcess Heat Injuring Fluids, Qi and Blood Stagnation. Pale purple or blue purple and moist indicatesCold Congealing Blood Stasis.
Green Tongue The tongue color resembles exposed “blue veins” on the skin, lacking red color, referred to as a green tongue.
Indicates Yang Deficiency, Excess Cold, Blood Stasis.
① Pale Blue Tongue with Thin White Coating. Indicates: Yang deficiency with cold congealing, fluids not rising; Yin cold with food. Diagnosis: Qi Deficiency with Blood Stasis. Can be seen in aplastic anemia, leukemia, etc.② Sharp Red Blue Purple Tongue with Green Coating. Indicates: Heat toxin injuring Yin; Yin deficiency with excess fire; stomach Qi and Yin exhausted, turbid rising; Nutritional Heat with Stasis. Diagnosis:Heat Toxin Injuring Yin, Blood Heat Stagnation. Can be seen in infectious febrile diseases in the exhaustion phase.③ Pale Blue Tongue with White Greasy Dry Coating. Indicates: Yin cold with food; cold dampness with blood stagnation; Yang deficiency with little fluids. Diagnosis:Yang Deficiency with Damp Stagnation and Blood Stasis. Can be seen in hemoglobinuria patients and Addison’s disease.Note: A completely blue tongue often indicates cold evil directly affecting the liver and kidneys, with Yang stagnation and failure to express. A blue tongue at the edges, or dry mouth with reluctance to swallow water, indicates internal blood stasis.
3. Observe Tongue Shape
1. Observe Old and Young TongueOld refers to a tongue with rough texture, firm and aged appearance, regardless of coating color, it indicatesExcess Syndrome.
1. Pale White Old Tongue with White Rough Coating. Indicates: Cold dampness blocking the channels, fluids not rising; sudden heat injuring fluids. Diagnosis: Blood Deficiency with Damp Stagnation. Commonly seen in various febrile diseases.2. Pale White Tongue with White Accumulated Powdery Coating. Indicates: Yang deficiency with heat floating; evil heat floating through the channels; internal heat gathering in the three burners. Diagnosis: Yang Deficiency with External Damp Heat. Commonly seen in various heart failure with secondary lung infection.3. Pale Red Tongue with White Tip and Yellow Root Coating. Indicates: Exterior evil entering the interior transforming into heat; damp heat and turbid internal accumulation; phlegm and turbid internal stagnation transforming into heat. Diagnosis:Exterior Evil Entering the Interior, Damp Turbidity Transforming into Heat. Can be seen in myocarditis, rheumatic fever and other febrile diseases.4. Pale Red Tongue with Half Yellow Gray Coating. Indicates: Yangming heat accumulation; Qi deficiency with little fluids, or with damp heat. Diagnosis:Damp Heat Transforming into Dryness, Qi Deficiency Not Moving. Can be seen in coronary heart disease, costochondritis, gastrointestinal diseases.Young refers to a tongue with delicate texture, plump and tender appearance, generally indicatingDeficiency Syndrome.
1. Pale Red Tongue with Thin White Coating. Indicates: External dryness evil; internal injury with Yin deficiency; normal tongue image in summer. Diagnosis: Normal person.2. Pale White Tongue with White Moist Slightly Thick Coating. Indicates: External cold dampness; evil transmitted half interior; spleen and stomach Yang deficiency. Diagnosis:Spleen Deficiency with Excess Dampness. Commonly seen in gastrointestinal bleeding, chronic renal failure, etc.3. Pale Red Shiny Tongue. Indicates: Dual deficiency of Qi and Yin; dual deficiency of Qi and Blood; stomach and kidney Yin injury. Diagnosis:Dual Deficiency of Qi and Yin. Can be seen in collagen disease, pulmonary infections and other febrile diseases.4. Pale Red Tongue with Transparent Coating. Indicates: Spleen and stomach Yang deficiency. Diagnosis:Spleen Deficiency Not Moving, Water Dampness Internal Stagnation. Can be seen in paroxysmal nocturnal hemoglobinuria, secondary anemia, etc.2. Observe Fat and ThinFat Tongue: Mostly indicatesInternal Water Dampness Stagnation
1. Pale White Tongue with Snowflake Coating. Indicates: Spleen Yang failure. Diagnosis: Spleen Yang Not Vibrant, Stomach Lacking Vitality. Commonly seen in chronic digestive system diseases, malnutrition, etc.2. Dark Red Fat Tongue with White Greasy Light Yellow Coating. Indicates: Exterior evil transforming heat into the interior; Yang deficiency with dampness, blood heat overflowing; damp heat phlegm rising; alcohol toxin counterflow. Diagnosis:Yang Deficiency with Water Stagnation, Blood Heat Stagnation. Can be seen in various heart disease patients with heart failure or infectious febrile diseases.3. Pale Purple Fat Tongue with Gray Yellow Greasy Coating. Indicates: Weak constitution with external evil entering the interior transforming heat; damp heat stasis, phlegm heat with stasis. Diagnosis:Yang Deficiency with Damp Stagnation, Transforming Heat Moving Wind. Can be seen in elderly tremor paralysis syndrome.4. Dark Red Teeth Marked Tongue with Peeling Coating. Indicates: Sudden heat injuring Qi and fluids; prolonged illness with Qi and Blood not continuing; blood stasis with damp heat, fluids not rising; blood heat and Qi and Blood stagnation. Diagnosis:Phlegm Qi Stagnation in the Liver Leading to Blood Stasis.Commonly seen in late-stage infectious febrile diseases, chronic active hepatitis, tumors, etc.Note:If the tongue is pale white, fat and tender, with slippery coating, it indicates spleen and kidney Yang deficiency, fluids not transforming, leading to water stagnation. If the tongue is pale red or red and fat, with yellow greasy coating, it mostly indicates spleen and stomach damp heat and phlegm turbidity.
Swollen Tongue: Indicates Alcohol Toxin or Heat Toxin RisingThe tongue body is enlarged, filling the mouth, and in severe cases cannot close, cannot retract, referred to as a swollen tongue.
1. Red Swollen Tongue with Yellow Tip and White Root Coating. Indicates: Evil heat internally residing, blood heat overflowing; damp toxin steaming, heat in the upper burner. Diagnosis:Damp Heat Steaming, Blood Heat Overflowing.2. Red Dark Swollen Tongue with Transparent Coating. Indicates: Heat stagnating in the Nutritional Blood, high fever injuring Yin; spleen and stomach weakness, dampness rising. Diagnosis: Damp Heat Accumulation, Transforming Dryness Injuring Yin, spleen Qi also injured. Can be seen in Staphylococcus aureus sepsis, sacroiliac joint infection, osteomyelitis.3. Dark Red Bumpy Swollen Tongue with Yellow Floating Coating. Indicates: Damp heat phlegm rising; heat toxin Qi stagnation and blood stasis. Diagnosis:Damp Heat Blood Stasis. Can be seen in vascular tumors of the tongue and other tumor diseases.4. Tongue Carbuncle. Indicates: Heat toxin in the blood, damp turbidity internally residing; heart channel toxin fire, spleen and kidney heat accumulation. Diagnosis:Damp Turbidity Internally Residing, Heat Toxin Entering the Blood. Can be seen in tongue cancer, etc. Causes include three: One is heat in the heart and spleen, tongue is often bright red and swollen, sometimes accompanied by pain. One is habitual drinking, also ill with warm heat, often seen with purple swollen tongue. One is due to poisoning leading to blood stagnation, resulting in a swollen tongue that is blue purple and dark.Thin Tongue The tongue body is thin and small, referred to as a thin tongue.
IndicatesDual Deficiency of Qi and Blood, Yin Deficiency with Excess Fire
① Pale White Tongue with Thin White Coating. Indicates: Spleen and stomach Yang deficiency; dual deficiency of Qi and Blood. Diagnosis:Yang Deficiency with Water Dampness Not Transforming. Commonly seen in anemia, chronic renal failure, etc.② Pale Red Thin Tongue with White Rough Coating. Indicates: Yin deficiency with excess fire; summer heat injuring Qi; sudden heat injuring fluids. Diagnosis:Phlegm Heat in the Lung. Commonly seen in viral infections such as adenoviral pneumonia.③ Pale Red Thin Tongue with Double Yellow Coating. Indicates: Dual deficiency of Qi and Blood; Yin deficiency with stomach heat. Diagnosis: Initial stage is heart and kidney Yang deficiency, water dampness overflowing; after treatment improvement, now it is Yin deficiency with stomach heat. Can be seen in chronic wasting diseases, heart disease, etc.④ Red Dark Thin Tongue with Yellow Petal Floating Coating. Indicates: Yin deficiency with excess fire; intestinal heat accumulation; excess heat syndrome. Diagnosis:Intestinal Heat Accumulation Injuring Yin. Commonly seen in severe infectious fever, dehydration, toxic bacteremia. Indicates dual deficiency of Qi and Blood and Yin deficiency with excess fire. A thin and pale tongue often indicates dual deficiency of Qi and Blood. A thin and red dry tongue often indicates Yin deficiency with excess fire, fluids consumed.3. Observe for Dots and Prickles
Dots refer to raised red, white, or black star-like spots on the tongue surface. Prickles refer to sharp spikes on the tongue surface, which not only enlarge but gradually form sharp points, rising like thorns, and touch them prickly. The appearance of various sizes and shapes of blue purple or purple black spots on the tongue surface, which do not protrude, is called stasis spots.
Indicates Internal Evil Heat
The tongue tip with prickles often indicates excessive heart fire, the tongue edges with prickles often indicate excessive liver and gallbladder fire, the tongue center with prickles often indicates excessive stomach and intestinal heat. If prickles are accompanied by yellow dry coating, it often indicates excessive heat in the Qi level.
5. Observe for Cracks
Cracks on the tongue surface of varying lengths and depths, with various shapes, are called cracked tongue.Its main diseases include three: one is excess heat injuring Yin; one is blood deficiency not moistening; one is spleen deficiency with dampness invading. A red dark tongue with cracks often indicates excess heat injuring fluids, or Yin deficiency with fluid depletion; A pale white tongue with cracks often indicates blood deficiency not moistening; If a pale white fat tender tongue has teeth marks and cracks, it indicates spleen deficiency with dampness invading.Smooth TongueThe tongue surface is smooth and shiny, without coating, referred to as a smooth tongue, also called “mirror tongue” or “shiny tongue”.
Indicates exhaustion of stomach Yin, severe injury to stomach Qi. Regardless of tongue color, it indicates a critical condition of stomach Qi about to fail. If pale white and shiny, it indicates spleen and stomach injury, extreme dual deficiency of Qi and Blood; If red dark and shiny, it indicates water depletion and fire inflammation, exhaustion of stomach and kidney Yin fluids.6. Observe for Teeth MarksTeeth marks on the edges of the tongue are called teeth-marked tongue or teeth-impressed tongue. Often seen with a fat tongue.
If pale white and moist, it indicates excessive cold dampness; if pale red with teeth marks, it often indicates spleen deficiency or Qi deficiency.
4. Observe Tongue Coating
Observe Tongue Coating
Tongue coating refers to a layer of coating on the tongue surface, produced by the spleen and stomach Qi vaporizing the turbid food in the stomach. Normal tongue coating is generally thin and even, with moderate moisture, slightly thicker in the middle and root of the tongue. Due to the strength and weakness of the patient’s stomach Qi, and the cold and heat of the pathogenic factors, various pathological tongue coatings can form. Observing tongue coating requires attention to changes in both coating quality and coating color.
1. Coating Quality
Coating quality refers to the texture and form of the tongue coating. Mainly observe changes in the thickness, moisture, greasiness, peeling, and true/false aspects of the tongue coating.
(1) Thin and Thick Coating
[Tongue Image Characteristics] The thickness of the tongue coating is measured by “seeing the bottom” or “not seeing the bottom”. If the tongue quality can be faintly seen through the coating, it is called thin coating, also known as visible bottom coating; if the tongue quality cannot be seen through the coating, it is called thick coating, also known as invisible bottom coating.[Clinical Significance] Mainly reflects the rise and fall of the pathogenic and righteous Qi and the depth of the pathogenic Qi. Thin coating indicates exterior syndrome, also indicates normal person, thick coating indicates interior syndrome, phlegm dampness, food accumulation.
(2) Moist and Dry Coating
[Tongue Image Characteristics] The tongue coating is moist with fluids, moderately dry and wet, neither slippery nor dry, referred to as moist coating. If there is excessive moisture on the tongue surface, extending the tongue causes it to drip, and it feels wet and slippery, it is called slippery coating. If the tongue coating is dry, feeling no moisture, and in severe cases, the coating cracks, it is called dry coating. If the coating is rough, it is called rough coating.
[Clinical Significance] Mainly reflects the abundance and distribution of fluids in the body.
[Mechanism Analysis] Moist coating is one of the manifestations of normal tongue coating, representing the stomach fluids and kidney liquids rising and covering the tongue surface. In the disease process, moist coating indicates that the body fluids have not been harmed, such as in wind-cold exterior syndrome, initial damp syndrome, food stagnation, blood stasis, etc.
(3)Greasy and Rotten Coating
[Tongue Image Characteristics] The coating is dense, with small particles merging into a sheet, appearing greasy, with thickness in the middle and thin at the edges, tightly adhering to the tongue surface, cannot be wiped off, and cannot be scraped off, referred to as greasy coating. If the coating is loose, with large particles, resembling tofu dregs piled on the tongue surface, thick in the middle and edges, easily wiped off, it is called rotten coating. If there is a thick layer on the tongue resembling pus, it is called purulent rotten coating.
[Clinical Significance] Mainly measures the rise and fall of Yang Qi and damp turbidity. Both indicate phlegm turbidity, food accumulation; purulent rotten coating indicates internal abscess.
[Mechanism Analysis] Greasy coating is often caused by internal damp turbidity, Yang Qi being restrained, and phlegm dampness accumulating on the tongue surface. Thin greasy coating, or greasy but not stagnant, often indicates food accumulation, or spleen deficiency with damp obstruction, blocking Qi mechanism; white greasy and slippery coating indicates phlegm turbidity, cold dampness internally obstructing, Yang Qi being restrained, Qi mechanism stagnation; thick greasy coating indicates sweet taste in the mouth, indicating spleen and stomach damp heat, evil gathering rising; yellow greasy and thick coating indicates phlegm heat, damp heat, summer heat and other evils internally accumulating, obstructing the bowel Qi.
The formation of rotten coating is often due to excess Yang heat, vaporizing the turbid evil in the stomach, accumulating on the tongue surface, indicating food accumulation in the stomach and intestines, or phlegm turbidity internally accumulating. Purulent rotten coating is often seen in internal abscess or evil toxin internally accumulating, indicating severe disease. In the course of the disease, if rotten coating gradually recedes, and new thin white coating appears, it indicates that the righteous Qi has overcome the evil, and the disease evil is dissipating; if rotten coating falls off and cannot regenerate new coating, it indicates that the disease has lasted long and the stomach Qi has declined, belonging to rootless coating.
(4)Peeling (Falling) Coating
[Tongue Image Characteristics] The tongue originally had coating, but during the disease process, the coating completely or partially falls off, leaving smooth areas without coating visible on the tongue quality.
According to the location and extent of the peeling coating, it can be divided into the following types: peeling of the anterior half of the tongue coating is called anterior peeling coating; peeling of the middle part of the tongue coating is called middle peeling coating; peeling of the root part of the tongue coating is called root peeling coating. If the coating peels off in many places, leaving only a small amount of coating on the tongue surface, it is called flower peeling coating; if the coating peels off around, leaving only a small central area, it is called chicken heart coating; if the coating completely peels off, leaving the tongue surface smooth as a mirror, it is called mirror tongue. If the coating peels off irregularly, with raised edges, clear boundaries, resembling a map, and the location changes from time to time, it is called map tongue. If the peeling areas of the coating are not smooth, with newly formed coating particles or visible tongue papillae, it is called pseudo-peeling coating.
[Clinical Significance] Generally indicates insufficient stomach Qi, exhaustion of stomach Yin, or dual deficiency of Qi and Blood, also a sign of overall weakness.
[Mechanism Analysis]The red tongue with peeling coating often indicates Yin deficiency; the pale tongue with peeling coating or pseudo-peeling coating often indicates blood deficiency or dual deficiency of Qi and Blood. Mirror tongue with red color indicates exhaustion of stomach Yin, a sign of severe Yin deficiency; a tongue that is pale white and smooth as a mirror, even lacking blood color, indicates severe blood deficiency, Yang Qi deficiency, and difficult to treat. If the tongue coating partially falls off, and the areas that have not peeled still have greasy coating, it often indicates deficiency of righteous Qi, phlegm turbidity not transformed, indicating a more complex condition.
The extent of peeling coating often correlates with the degree of Qi and Yin or Qi and Blood deficiency. The areas of peeling often correspond to the distribution of the internal organs on the tongue surface.
Note: The differentiation of peeling coating should also be distinguished from congenital peeling coating. Congenital peeling coating is a peeling coating that is present from birth, often located in the central groove of the tongue surface, presenting a diamond shape, often due to congenital developmental defects.
Observing the peeling can measure the existence of stomach Qi and stomach Yin, judging the prognosis of the disease. A completely peeled tongue indicates the disease as previously mentioned, flower peeling coating is also caused by injury to both stomach Qi and Yin. If flower peeling coating is accompanied by greasy coating, it often indicates phlegm turbidity not transformed, righteous Qi has been injured, indicating a more complex condition. Pseudo-peeling coating indicates prolonged illness with Qi and Blood not continuing.
(5) Partial and Full Coating
[Tongue Image Characteristics] The tongue coating covers the entire tongue surface, referred to as full coating. If the coating is only distributed in the front, back, left, or right part, it is called partial coating.
[Clinical Significance] When full coating is seen in the disease, it often indicates scattered pathogenic Qi, mostly a sign of damp phlegm obstruction. If the coating is partial, it often indicates that the corresponding internal organ has pathogenic Qi stagnation.
[Mechanism Analysis] If the coating is biased towards the tip of the tongue, it indicates that the pathogenic Qi has not deeply entered the interior, while the stomach Qi has already been injured; if the coating is biased towards the root of the tongue, it indicates that the external evil has retreated, but the stomach is still stagnant; if the coating is only seen in the middle of the tongue, it often indicates phlegm and food stagnation in the middle burner; if the coating is biased to the left or right, it indicates…
Partial coating should be distinguished from peeling coating; partial coating is a pathological phenomenon in the distribution of tongue coating, not peeling coating that originally had coating and then fell off, causing the coating to appear biased in a certain area. If one side of the teeth is lost, resulting in less friction, causing that side of the tongue coating to be thicker, it is also different from pathological partial coating.
(6) True and False Coating
[Tongue Image Characteristics] The tongue coating tightly adheres to the tongue surface, difficult to remove, and after scraping, it still leaves traces of coating, not revealing the tongue quality, the coating appears to grow from the tongue body, referred to as rooted coating, which is true coating. If the tongue coating does not tightly adhere to the tongue surface, does not appear to grow from the tongue, is easily scraped off, and after scraping, the tongue quality is clean, it is called unrooted coating, which is false coating.
[Clinical Significance] Important for distinguishing the severity of the disease and prognosis.
[Mechanism Analysis] The determination of true and false coating is based on whether it is rooted or unrooted. True coating is formed by the spleen and stomach Qi vaporizing the turbid food and other evils accumulating on the tongue surface, hence the coating is inseparable from the tongue body. False coating is due to the deficiency of stomach Qi, unable to regenerate new coating, and the old coating gradually detaches from the tongue body, floating on the tongue surface, hence the coating is unrooted. In the early and middle stages of the disease, if the tongue shows true coating and is thick, it indicates that the stomach Qi is obstructed, and the disease is more severe; if true coating is seen in a long-term illness, it indicates that the stomach Qi is still present.
If new disease appears with false coating, it indicates that the evil turbid is gradually accumulating, and the disease is lighter; if long-term illness appears with false coating, it indicates that the stomach Qi is deficient, unable to rise, and the disease is severe. If a thick coating floats on the tongue surface, appearing unrooted, and after scraping, a thin new coating appears, it indicates a good sign of recovery from the disease.
2. Coating Color
The changes in coating color mainly include white coating, yellow coating, gray-black coating, which can appear alone or in combination. Various changes in coating color need to be analyzed in conjunction with coating quality, tongue color, and tongue shape changes.
(1) White Coating
[Tongue Image Characteristics] The coating attached to the tongue surface appears white. White coating can be thin or thick; if the coating is white and thin, and the tongue body can be seen through the coating, it is called thin white coating; if the coating is white and thick, and the tongue body cannot be seen through the coating, it is called thick white coating.
[Clinical Significance] It can be normal tongue coating, but in disease, it often indicates exterior syndrome, cold syndrome, damp syndrome; in special cases, white coating can also indicate heat syndrome, such as accumulated powdery coating, rough cracked coating.
[Mechanism Analysis] White coating is the original color of tongue coating, the most common coating color, and other coating colors can all be transformed from white coating.
Thin white and moist coating can be a normal tongue image, or indicate the initial stage of exterior syndrome, or a mild interior syndrome, or Yang deficiency with internal cold. Thick white and greasy coating often indicates internal stagnation of dampness, or phlegm and food accumulation. Thick white and dry coating indicates phlegm turbidity and damp heat internally accumulating; white coating resembling accumulated powder, feeling not dry, is called accumulated powder coating, often seen in epidemics or internal abscesses, formed by the combination of turbid dampness and heat toxin. White coating that is dry and cracked, rough like sand, indicates dryness heat injuring fluids, Yin liquid deficiency.
(2) Yellow Coating
[Tongue Image Characteristics] The coating appears yellow. Depending on the degree of yellow, there are light yellow, deep yellow, and burnt yellow. Light yellow coating is also called slightly yellow coating, appearing light yellow, often transformed from thin white coating; deep yellow coating is also called standard yellow coating, appearing yellow and thick; burnt yellow coating is also called old yellow coating, which is standard yellow with gray-black coating mixed in. Yellow coating is often distributed in the middle of the tongue, but can also cover the entire tongue. Yellow coating often appears simultaneously with red dark tongue.[Clinical Significance] Indicates heat syndrome, interior syndrome.[Mechanism Analysis] The evil heat scorching the tongue causes the coating to appear yellow. The yellower the coating, the more severe the heat evil; light yellow coating indicates light heat, deep yellow coating indicates severe heat, burnt yellow coating indicates extreme heat.
Light yellow indicates light heat, deep yellow indicates heavy heat, burnt yellow indicates heat accumulation. In external diseases, if the coating changes from white to yellow, it indicates that the exterior evil has entered the interior and transformed into heat. Thin light yellow coating is also often seen in external wind-heat exterior syndrome or wind-cold transforming into heat. If the tongue is pale, fat, tender, and the coating is yellow and slippery, it often indicates Yang deficiency with water dampness not transforming.
(3) Gray-Black Coating
[Tongue Image Characteristics] The coating appears light black, referred to as gray coating; if the coating appears deep gray, it is called black coating. (Gray coating and black coating are only different in color depth, hence often referred to as gray-black coating.) The distribution of gray-black coating is deeper near the central groove of the tongue, gradually becoming lighter towards the tip of the tongue. Gray-black coating often transforms from white coating or yellow coating, and usually appears after the disease has persisted for a certain period and developed to a considerable extent.
[Clinical Significance] Indicates internal excess cold, or extreme heat in the interior.
[Mechanism Analysis] Gray-black coating can be seen in heat diseases, and can also be seen in cold damp diseases, but regardless of cold or heat, it indicates a severe condition; the deeper the black color, the more severe the disease. As stated in the “Aoshi Cold Damage Golden Mirror Record”: “If the tongue shows black color, water overcomes fire, those who have this are almost impossible to cure.” It also states: “If the tongue base appears as black lacquer-like shine, the chance of survival is very low.” However, there are also cases of gray-black coating with mild disease, or even without obvious symptoms, such as excessive smoking.
The moisture and dryness of gray-black coating are important indicators for distinguishing the cold and heat properties. In cold damp diseases, gray-black coating often transforms from white coating, and the tongue coating is gray-black and must be moist with plenty of fluids; in heat diseases, gray-black coating often transforms from yellow coating, and the tongue coating is gray-black and must be dry without fluids.
If the tongue edges and tip show white greasy coating, while the middle and root of the tongue show gray-black coating, with a moist tongue surface, it often indicates Yang deficiency with internal excess cold, or phlegm dampness internally stagnating.
If the tongue edges and tip show yellow greasy coating, while the middle of the tongue shows gray-black coating, it often indicates damp heat internally accumulating, not transforming for a long time.
If the coating is burnt black and dry, with cracks and prickles, regardless of external or internal injury, it indicates extreme heat and fluid depletion. If the coating is burnt black and slippery, it often indicates internal excess cold and Yang deficiency. If the coating is burnt black and dry, with cracks and prickles, it often indicates extreme heat and fluid depletion. If the coating is burnt black and slippery, it often indicates internal excess cold and Yang deficiency.
White Gray CoatingGray coating: gray refers to light black. 
Indicates interior syndrome, commonly seen in interior heat syndrome, also seen in cold damp syndrome. Gray coating that is dry often indicates extreme heat injuring fluids, can be seen in external heat diseases; or indicates Yin deficiency with excess fire, commonly seen in internal injury mixed diseases. Gray coating that is moist indicates phlegm dampness internally stagnating, or indicates cold dampness internally obstructing.
Black Coating
Black coating: black coating is darker than gray coating, often develops from gray coating or burnt yellow coating, commonly seen in severe stages of epidemic diseases. Indicates interior syndrome, or extreme heat, or excess cold. 
If the coating is black and dry, with cracks and prickles, it often indicates extreme heat and fluid depletion. If the coating is black and slippery, it often indicates internal excess cold and Yang deficiency. If the coating is black and dry, with cracks and prickles, it often indicates extreme heat and fluid depletion. If the coating is black and slippery, it often indicates internal excess cold and Yang deficiency.
Green Coating
none;”> Green coating often transforms from white coating, regardless of light green or dark green, its significance is the same as gray-black coating, but it indicates heat rather than cold. If the tongue is covered with slippery coating, with green appearing in between, it indicates damp heat phlegm, belonging to the evil of Yin transforming into heat, often seen in epidemics, damp-warm diseases.
Fermented Sauce Coating Fermented sauce coating is a coating color that is red with black, also mixed with yellow, resembling fermented sauce, hence the name. It is often due to the stomach and intestines having accumulated turbid dampness, which has transformed into heat over time. Therefore, it is said that fermented sauce coating indicates the disease of prolonged damp heat, commonly seen in food accumulation with heat stroke, food accumulation injuring the Taiyin, or internal heat accumulating for a long time.
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