The Tongue and Mouth: A Mirror of Digestion and Inner Health

Farzollah Gholizadeh and Fariba Bayrami

Colour, coating, moisture, cracks and changes in the mouth — what messages do they give us?

When you wake up in the morning, before brushing your teeth, look at your tongue in the mirror for a few seconds.

What colour is it?
Is it pink and shiny, or white, yellow, red or dark?
Is there a coating on it?
Is the coating thin or thick?
Is the tongue dry, or overly moist?
Can you see cracks, swelling, tooth marks, sores or spots on it?
What taste is there in your mouth?
How does your breath smell?

You may think these are only matters of oral hygiene. Yet in Avicennian–Greek (Unani) medicine and in many schools of traditional medicine, the tongue and mouth are among the most important visible areas of the body for understanding a person’s inner state.

Modern medicine also knows that some general diseases, nutritional deficiencies, hormonal (endocrine) problems and digestive diseases can show signs on the tongue and the lining of the mouth.

So sometimes all we need to do is open our mouth; the body itself offers us clues about its inner state.

But let us keep one principle in mind from the start:

The tongue alone does not diagnose disease; the tongue gives clues.

The art of diagnosis is being able to read these clues as a whole.

Why is the tongue important for understanding the state of the body?

The tongue is one of the visible organs of the body with the richest nerve and blood supply, and it is in constant interaction with saliva, food, the microorganisms of the mouth and the body’s internal environment.

The colour and appearance of the tongue can be affected by many factors:

The body’s fluid balance
Saliva
Diet
Oral hygiene
The oral microbiota
Medicines
Cigarettes and tobacco products
Infections
The body’s general condition
Some nutritional deficiencies
And some diseases

In Avicennian–Greek medicine, too, the tongue and mouth are regarded as part of a wider system, “dalail and alamat” (signs and indications).

Physicians did not only ask about the colour of the tongue; they paid attention to colour, moisture, dryness, coating, consistency, movement, sensation, the taste in the mouth, saliva and breath odour, and assessed these together with the pulse, urine, stool, appetite, thirst, sleep and other signs.

The tongue: the mirror of digestion

One of the most important connections in Avicennian–Greek medicine is the relationship between the stomach and digestive system and the tongue and mouth.

According to the old physicians, if digestion does not work properly, its effects may show up in appetite, belching, bloating, the taste in the mouth, breath odour and the quality of the tongue.

Traditional texts also point to the effect of vapours and matter rising from the stomach on the state of the mouth and tongue.

Put simply:

Sometimes the problem is not only on the tongue; its root should be sought further down, in the digestive system.

That is why, in a traditional examination, a practitioner who sees an abnormal tongue may ask:

How is your appetite?
Do you feel heavy after eating?
Do you have bloating?
Do you belch often?
Do you have heartburn (reflux)?
What taste do you have in your mouth in the morning?
Is there constipation or diarrhoea?

These questions are not random; the tongue should be read together with digestion.

What does a healthy tongue look like?

The appearance of a healthy tongue varies from person to person, but a normal tongue usually:

Has a pink colour that suits the person’s natural mucosa.
Is relatively moist.
Moves normally.
Has natural papillae (buds) on its surface.
May have a thin, limited coating.
Shows no lasting sores, swelling or unusual change in colour.

The important point is this:

A “completely uncoated tongue” is not necessarily a measure of health; a thin, natural coating on the tongue can be part of the normal state of the mouth.

What really matters is the change compared with the person’s usual state.

The first sign: the colour of the tongue

Colour is one of the first features that stands out in a tongue examination.

But the colour of the tongue alone is not enough to diagnose a disease.

Pale tongue

In the logic of traditional medicine, paleness may be linked to coldness, weakness and a reduction in the quality or quantity of the blood.

In modern medicine, too, if the tongue and other mucous membranes become unusually pale — especially together with fatigue, weakness, dizziness or shortness of breath on exertion — the state of the blood and anaemia are among the things that should be investigated.

In other words:

Paleness is a clue; it is not a definite diagnosis of anaemia.

What does a red tongue tell us?

In traditional medicine, increased redness of the tongue — especially with dryness, thirst and a feeling of heat — is mostly interpreted as a sign of increased heat (hararet).

But a red tongue can have other causes too.

Some inflammations, infections, nutritional deficiencies and other conditions can also change the colour of the tongue.

So the practitioner should not only ask, “Is the tongue red?” but also:

Is it red and dry, or red and moist?
Is there a coating or not?
Is the whole tongue red, or only part of it?
Is there also burning or pain?

These small differences can change the meaning of the sign.

Yellow tongue: bile, or something else?

In the logic of humoral medicine, yellowness can draw our attention to the quality of the yellow bile and to increased heat and dryness.

However, yellowing of the tongue tissue itself and a yellow coating on the tongue must be told apart.

These two are not the same thing.

The tongue coating can also change colour because of bacteria in the mouth, hygiene, dry mouth, food, smoking and other factors.

Even this simple point shows why reading the tongue is much more than seeing a colour.

Tongue coating: perhaps more important than colour

One of the most interesting parts of a tongue examination is the layer on the tongue — the tongue coating.

The tongue coating is made up of various substances, cells, bacteria and debris that build up on the surface of the papillae.

In traditional medicine, it is not only the colour of this coating that matters.

The practitioner should look at:

Is it thin or thick?
Is it dry or moist?
Does it come off easily, or is it sticky?
Does it cover the whole tongue, or only part of it?
Is it white, yellow or another colour?
Does it quickly form again after being cleaned?

So two people may both have a “white tongue”, yet their conditions may not mean the same thing.

A white tongue does not always mean the same thing

This is one of the common mistakes on social media.

It is not possible to link every white tongue to a single disease, to fungus or to a stomach problem.

A white coating can form for different reasons.

In the logic of traditional medicine, whiteness together with coldness, dampness (rutubet), a feeling of heaviness and clear digestive complaints carries a different meaning from whiteness seen with marked dryness.

On the other hand, a white coating that can be wiped off, together with certain complaints, may call for investigation of some oral conditions, including fungal infection.

So in reading signs:

Don’t assess colour separately from thickness, moisture, location and the accompanying symptoms.

Dry tongue: it is not just thirst

Dryness of the tongue is one of the important signs.

Sometimes the cause is simple:

The person has not drunk enough water, has breathed through the mouth, has been in a dry environment or has talked for a long time.

But constant dryness of the mouth and tongue can also be linked to other factors, such as:

Reduced saliva production
Some medicines
Older age
Some salivary gland diseases
Some systemic diseases

In traditional medicine, too, tongue dryness becomes important — together with thirst, heat, the pulse and other signs — for understanding increased dryness or heat.

Saliva: one of the signs we pay little attention to

Saliva is not only there to keep the mouth moist.

It plays a role in chewing, swallowing, speaking, protecting the mouth’s environment and protecting the teeth.

In reading signs, attention should be paid to the amount and quality of saliva.

Is the mouth constantly dry?
Does saliva build up excessively?
Is it thick or watery?
Is it different in the morning?
Does it come with an unusual taste in the mouth?

In traditional medicine, the quality of saliva is assessed together with the state of digestion and the temperament.

Sometimes what a person thinks is a “tongue problem” is actually more closely linked to a change in saliva production.

What do tooth marks on the edges of the tongue tell us?

Sometimes the tongue is wider or swollen, and the marks of the teeth stay on its edges.

In traditional medicine and some schools of Eastern medicine, this appearance is considered together with other signs and may be interpreted in terms of dampness, the state of digestion and the quality of the body’s functioning.

But in modern medicine, too, a scalloped tongue can have different causes and does not by itself point to a specific disease.

So here too, the more important question is:

What other symptoms come with it?

Tongue cracks: not every crack is a disease

Some people are born with a grooved or fissured tongue, and this can continue without problems for years.

But it is different if the cracks come with dryness, pain, inflammation, a change in colour or a new change.

In traditional medicine, too, the type and depth of the crack, whether the tongue is dry or moist, and other accompanying signs matter in interpretation.

So just seeing a crack is not enough to draw a conclusion.

Smooth, shiny tongue: think about nutrition too

Sometimes the tongue loses its natural budded texture and looks smooth, shiny or more sensitive.

This kind of change can be seen in some nutritional and blood conditions.

In a clinical assessment, the status of iron, vitamin B12, folate and some other factors may come up.

If this appearance comes with paleness, fatigue, weakness, a burning tongue or other symptoms, it is worth a closer look.

But again:

A specific deficiency cannot be fully diagnosed from the appearance of the tongue alone.

Burning in the tongue and mouth

Sometimes the tongue looks almost normal, but the person complains of burning.

A burning feeling can be linked to different causes, such as dry mouth, local irritation, some nutritional deficiencies, oral problems, some diseases and even nervous and psychological factors.

In traditional medicine, too, one should look at how the burning relates to heat, dryness, thirst, the colour of the tongue and the state of digestion.

So what the patient feels is as important as how the tongue looks.

The taste in the mouth: a forgotten sign

Bitterness, sourness, unusual sweetness, saltiness or a metallic taste in the mouth can offer some clues.

In Avicennian–Greek medicine, a change in the taste in the mouth is assessed together with appetite, thirst, digestion, the tongue and other signs.

But modern medicine also knows that a change in the sense of taste can have very different causes: from medicines and oral diseases to infections and some general disorders.

So a “bitter mouth” on its own does not mean a specific liver or gallbladder disease.

Bad breath: not always a stomach problem

One of the most common beliefs is this:

“Bad breath comes from the stomach.”

Digestive problems can sometimes play a role, but in most cases of bad breath the source is the mouth itself.

Microbial plaque, the tongue, gum disease, dental problems and dry mouth are important causes.

Post-nasal drip and some nose and sinus problems can also play a role.

That is why, if a person has only their stomach treated for bad breath for years, and the tongue, teeth, gums, saliva and throat are not examined, the real cause may be missed.

The gums speak too

Oral health is not limited to the tongue.

Healthy gums usually do not bleed often, do not swell and do not pull away from the teeth.

Recurring gum bleeding calls for an examination of the gums and oral hygiene rather than being treated as a simple sign of temperament.

But if unusual gum bleeding comes with easy bruising or other bleeding in the body, a more thorough assessment also becomes important.

Mouth sores and ulcers

Occasional mouth ulcers are quite common.

But if mouth sores recur often, are numerous, very large or long-lasting, or come with other symptoms in the body, they should be looked at more carefully.

Some digestive, inflammatory and immune diseases and nutritional deficiencies can occur together with mouth sores.

In traditional medicine, too, with mouth sores it is not only the location of the lesion that matters; heat, colour, pain, moisture, discharges and the body’s other signs are also taken into account.

The mouth and the gut: a connection sometimes seen on the tongue

The relationship between the digestive system and the mouth is not only a traditional concept.

Today we know that some digestive diseases can also show signs in the mouth.

For example, in some inflammatory bowel diseases, coeliac disease and malabsorption disorders, changes can be seen in the mouth or on the tongue.

This does not mean that bowel disease can be diagnosed with certainty by looking at the tongue.

The correct meaning is this:

Sometimes the mouth is the first place that leads us to ask more questions about the digestive system.

The tongue and blood sugar

Diabetes and long-term high blood sugar can also affect the environment of the mouth.

In people with diabetes, dry mouth, increased susceptibility to some infections and gum problems are of greater importance.

If constant dry mouth comes with excessive thirst, frequent urination, fatigue or unusual weight change, it makes sense to have blood sugar checked.

Still, the tongue does not diagnose diabetes; the overall picture of symptoms shows the direction of investigation.

The tongue and the immune system

Some changes in the mouth can also be seen in diseases linked to the immune system.

Severe dry mouth, recurring sores or certain mucosal changes are sometimes part of a bigger picture.

So if lesions in the mouth keep recurring, they should not always be explained only by “heat” or “cold”.

Temperament is one layer of assessment; a possible disease is another.

The mouth, the liver and bile

In Avicennian–Greek medicine, the quality of the bile, digestion and the functioning of the body’s main organs may be considered together with the taste, colour and state of the mouth.

A bitter mouth, dryness, thirst and some changes in the tongue, together with other signs, may lead a traditional practitioner to examine the state of the bile and digestive system.

But there is a very important point:

A bitter mouth ≠ liver disease.

To assess liver disease, the overall picture of symptoms and, when needed, tests and medical examinations must be taken into account.

Geographic tongue: a condition that looks strange but is not always dangerous

Sometimes some areas of the tongue’s surface lose their natural buds and patches form with clear borders, whose place and shape change over time.

This condition is known as “geographic tongue” .

Its appearance can worry a person, but it is usually benign.

This example shows why recognising signs correctly matters:

Not every unusual appearance is necessarily a sign of a dangerous disease.

Hairy or dark tongue

Sometimes the buds on the surface of the tongue grow longer and substances and pigments build up on them; as a result the tongue can look dark, even hairy.

Factors such as oral hygiene, smoking, some medicines, dry mouth and changes in the microbial environment of the mouth can play a role in this.

So seeing a dark tongue is not, on its own, evidence of an internal organ disease.

A very important principle: separate the “tongue body” from the “tongue coating”

Let’s say two people have a yellow tongue.

In the first person, the tongue body itself has changed colour.

In the second person, the body is almost normal, but there is a yellow coating on the tongue .

From a sign-reading point of view, these two situations do not necessarily mean the same thing.

The same applies to whiteness and some other colours.

One of the most important skills in tongue examination is for the practitioner to learn to tell apart:

What is the tongue’s own colour, and what is the colour of the coating on it?

This small difference sometimes completely changes the direction of the interpretation.

Are different areas of the tongue linked to different organs of the body?

Different schools of traditional medicine have paid attention to different areas of the tongue.

Avicennian–Greek medicine, Traditional Chinese Medicine and other traditional systems each have their own methods for interpreting the tongue, and in some of them different areas of the tongue are considered in relation to different functions of the body.

But this is one of the subjects that must be learned through proper training.

Seeing a spot on one part of the tongue and immediately saying, “This area belongs to such-and-such organ, so that organ is diseased,” is not a scientifically or clinically sound method.

Location + colour + coating + moisture + shape + other signs

must be assessed together.

How can temperament be understood from the tongue and mouth?

In Avicennian–Greek medicine, the tongue alone is not enough to determine temperament, but it can be part of the picture.

In general:

Heat
May be seen with increased redness, a feeling of heat, thirst or certain accompanying signs.

Dryness
Fits with reduced moisture, a drying surface and sometimes cracking more easily.

Moisture (rutubet)
May come with increased moisture in the mouth, softness and certain types of tongue coating.

Coldness
Together with other signs, may be seen with paleness, more moisture or fewer signs of heat.

But determining whether a person is sanguine, choleric, phlegmatic or melancholic requires observing the whole body and taking the patient’s history.

The tongue is one of the witnesses; it is not the judge who gives the final verdict.

When should the tongue and mouth be examined?

To make better comparisons, it is best to observe the tongue under relatively constant conditions.

Coloured foods and drinks, tea and coffee, smoking, some medicines, brushing the tongue and mouthwashes can temporarily change the appearance of the tongue.

So an observation in the morning, before eating or drinking and before cleaning the tongue, can be useful for comparing different days.

But a single observation is not enough.

A lasting pattern and change compared with the past matter more than a random snapshot.

Five golden questions when reading the tongue

If you have noticed a change in your tongue, ask these before drawing any conclusion:

Has the tongue’s own colour changed, or only the coating on it?
Is the tongue dry or moist?
Is the coating thin, or thick and sticky?
Is this change lasting, or does it only appear now and then?
What happened in the same period with digestion, appetite, thirst, elimination, energy and other parts of the body?

These five questions move your view from “seeing the tongue” to “reading the tongue”.

Which changes should not be ignored?

It is better to have some changes in the mouth and tongue examined by a doctor or dentist, especially:

A mouth sore lasting longer than about two weeks
A lasting, unexplained white or red patch
A new lump or hardness
Unexplained bleeding
A new problem with swallowing
Constant pain or numbness
A marked and lasting change in tongue colour
Unusual swelling of the tongue
Severe, constant dry mouth
A lesion that keeps growing or changing

These conditions should not be attributed only to temperament or stomach problems.

The big mistake: don’t link every tongue sign to a single disease

Many images are shared on social media:

“If the tip of your tongue is red, such-and-such organ is diseased.”
“If the edge of your tongue is scalloped, you definitely have such-and-such problem.”
“If your tongue is white, you definitely have a fungal infection.”
“If your tongue is yellow, there is a problem with your liver.”

The body is much more complex than these formulas.

One sign can have more than one cause, and one disease can show up through different signs.

Real assessment comes from the combination of signs .

Conclusion: the body sometimes gives signs before it suffers

The tongue and mouth are in front of our eyes every day, yet we rarely truly see them.

The colour of the tongue, the type of coating, moisture, dryness, cracks, swelling, tooth marks, saliva, the taste and smell of the mouth — each can be part of a bigger picture.

In Avicennian–Greek medicine, these signs have been assessed for centuries together with the state of the stomach and digestion, the quality of the humours, the body’s heat and moisture and the functioning of other organs.

Modern medical knowledge also shows that some blood and nutritional disorders, oral diseases, diabetes, digestive diseases, immune disorders and many other factors can show themselves in the mouth and on the tongue.

But the real secret is not in a colour or a crack.

The secret is in the combination of signs.

A white tongue alone is not a diagnosis.
A red tongue alone is not a diagnosis.
A crack, a bitter taste or a tooth mark alone is not a diagnosis either.

In real sign-reading, you need to ask:

What changed?
Since when?
Together with what other symptoms?
And what pattern do all these signs form together?

This is where the difference between looking at the body and reading the body becomes clear.

Many people see their tongue in the mirror every day, but far fewer know how to interpret its colour, coating, moisture, shape and other signs together.

And this subject is too broad to cover in full in a single article.

The colour types of the tongue body, types of coating, the difference between white and yellow coating, the thickness and rootedness of the coating, cracks, swelling, tooth marks, spots, sores, moisture, saliva, tastes, how the signs relate to digestion and the humours, and above all how to reach a clinical interpretation by combining several signs — each of these is a topic of its own.

The aim of this article was to open a window:

Before the body speaks through pain, it sometimes speaks through signs; the tongue is one of the clearest places where this conversation can be seen.

References

Avicenna (Ibn Sina). Al-Qanun fi al-Tibb (The Canon of Medicine); Book One and the sections on indications, temperament, the mouth, the tongue and the digestive system.
Rhazes (al-Razi), Muhammad ibn Zakariya. Al-Hawi fi al-Tibb.
Jurjani, Sayyid Ismail. Zakhira-i Khwarazmshahi.
Aghili Khorasani, Mohammad Hosein. Kholasat al-Hikmah.
Classical sources of Avicennian–Greek medicine on signs, digestion, the humours and the states of the tongue and mouth.
Byrd JA, Bruce AJ, Rogers RS. Glossitis and other tongue disorders. Dermatologic Clinics. 2003.
Mangold AR, Torgerson RR, Rogers RS. Diseases of the tongue. Clinics in Dermatology. 2016.
Chiang CP, Chang JYF, Wang YP, Wu YH, Wu YC, Sun A. Atrophic glossitis: Etiology, serum autoantibodies, anemia, hematinic deficiencies, hyperhomocysteinemia, and management. Journal of the Formosan Medical Association. 2020.
Clinical sources on oral diseases and the oral signs of systemic diseases.
Dr Kalan scientific and educational resources.

Please note

This article is for information only and is based on traditional medicine sources and general nutrition knowledge. It is not a medical diagnosis, treatment or prescription and does not replace an examination by a doctor. If you have a complaint, take regular medication, are pregnant, or are considering this for your child, talk to your doctor before changing your diet or using herbs. Herbal products can interact with medicines.