Mouth and Lips

My tongue is red and smooth: a deficiency, thrush or something else?

When the small bumps on the surface of the tongue disappear, the tongue becomes smooth and red; the places to look for the cause follow a set order

The surface of your tongue is not as rough as it used to be; it looks smooth, shiny and red, and it burns when you eat something hot or spicy. The medical name for this picture is atrophic glossitis, meaning thinning of the surface of the tongue. It is not a disease in itself but a sign: behind it there is often a lack of B12, iron or folic acid, oral thrush or a dry mouth, and these are often present together. Below you will find which causes a smooth red tongue comes from, what is looked at in the mirror and in a blood test, why settling for a single test is misleading, and which sign means seeing a doctor without waiting.

Short answer

A smooth, shiny, red tongue shows that the small bumps on its surface (papillae) have disappeared. The commonest causes are a lack of B12, iron or folic acid, oral thrush and a dry mouth; often several are present together. Alongside a full blood count, B12, folate and ferritin (iron stores) should be measured; if thrush is suspected, a dental examination is needed. If the burning tongue comes with numbness, tingling, unsteadiness or forgetfulness, see your GP (family doctor) without delay. If your tongue is swelling quickly and breathing or speaking is becoming difficult, call 112.

The medical name: Atrophic glossitis (thinning of the tongue surface)
The commonest causes: Lack of B12, iron or folate; thrush; a dry mouth
Tests to ask for: Full blood count, B12, folate, ferritin
See a doctor without waiting: If numbness, tingling or balance problems come with it

Why the tongue becomes smooth and red

The upper surface of a healthy tongue is covered with thousands of small bumps called papillae; these give the tongue its velvety texture and slightly whitish-pink colour. This layer is one of the fastest-renewing tissues in the body and needs a constant supply of iron, B12 and folic acid to renew itself. When the building blocks run short, or the surface is constantly irritated, the papillae shrink and disappear. The thin tissue underneath, rich in blood vessels, looks bright red from the outside. Cleveland Clinic describes inflammation of the tongue (glossitis) as the tongue looking smooth and shiny, being sore, and turning red and swollen.

The best-known cause is a vitamin and mineral deficiency. The NHS lists a sore or red tongue, sometimes with mouth ulcers, among the symptoms of anaemia due to a lack of B12 or folate. MSD Manuals writes that a pale, smooth tongue can come from iron deficiency anaemia or from pernicious anaemia due to B12 deficiency, while a smooth red tongue can also be seen in pellagra, which is due to a lack of niacin (vitamin B3). In a study in China comparing 236 patients with atrophic glossitis with 208 healthy people, 68.22% of the patients had B12 deficiency, 13.98% had ferritin deficiency and 21.61% had anaemia. When more than half or all of the tongue surface had become smooth, B12 deficiency was more common.

The second major cause is oral thrush (candida). Thrush does not always appear as white plaques that can be wiped off; it can also show itself as a red, burning and smooth tongue. In a study of 124 patients with atrophic glossitis in the Chinese city of Qingdao, a fungal infection was found in 79.03% of the patients, a dry mouth in 41.94%, anaemia in 48.39%, B12 deficiency in 29.03% and ferritin deficiency in 22.58%. The fact that the rates in the two studies are so different actually gives the most important lesson: the same appearance comes from different causes in different patients, and the causes often overlap.

The third cause is a dry mouth. Saliva both moistens the surface of the tongue and limits the overgrowth of fungus. In a study in Japan of 231 patients complaining of a dry mouth, the two factors most closely linked to atrophic glossitis were an increase in the amount of the fungus Candida albicans and a reduced stimulated flow of saliva. In other words, in a dry mouth the fungus multiplies easily and smooths the surface of the tongue; in this situation, giving antifungal medicine alone can lead to the picture coming back unless the cause of the dryness is found.

The deficiency itself has a cause too, and that cause is often not diet. The NHS lists among the common causes of B12 deficiency pernicious anaemia, in which the immune system attacks the stomach, stomach operations, bowel diseases such as Crohn's disease, a plant-based diet and certain medicines; for medicines, it gives as examples the stomach-protecting proton pump inhibitors (PPIs) and the diabetes medicine metformin. For folate deficiency, it lists absorption problems such as coeliac disease, certain epilepsy medicines and methotrexate.

The timing can be misleading. The NHS writes that the body's B12 stores can last around 2 to 5 years without being replenished, so it can take a long time for problems to appear after a change in diet. Folate stores, on the other hand, usually last around 4 months. According to the NHS, some of these symptoms can also be seen before anaemia develops. Reading these two pieces of information together gives a practical conclusion: a full blood count that comes back normal is not enough to explain the picture in the tongue; B12, folate and ferritin need to be measured separately.

A smooth red tongue can be confused with other pictures. Geographic tongue also has smooth red areas, but these have a white border and move within days. If there is a single smooth red diamond-shaped area in the middle, towards the back of the tongue, it may be median rhomboid glossitis; the review in the American Family Physician journal writes that this can be linked to fungus and, if there are symptoms, usually improves with antifungal treatment. Cleveland Clinic also lists allergy to foods, medicines or dental care products, spicy food, alcohol and tobacco, injury inside the mouth and appliances in the mouth such as dentures among the causes of inflammation of the tongue.

There is also data on why this picture should be followed up. In a large case-control study in people over 65 in the USA, a previous diagnosis of inflammation of the tongue was present in 6.0% of those with tongue cancer and 0.6% of those without cancer. This is an observational study; it does not show that inflammation of the tongue turns into cancer, and most smooth red tongues come from a harmless cause. But it suggests that inflammation of the tongue that lasts for months without a cause being found, or does not respond to treatment, should not be forgotten and should be followed up with regular examinations.

Which picture suggests which cause

The first list describes the signs that suggest the more common causes with simple treatment; the second list describes the pictures that call for seeing a doctor without waiting or for further assessment. Examination and a blood test make the definite distinction.

When it fits

The whole tongue is smooth, and there is tiredness and shortness of breath tooIf widespread smoothing comes together with weakness, tiring quickly and palpitations, anaemia and a lack of B12, iron or folate are the first causes that come to mind. Your GP will request a blood test.
You wear a denture, and the palate is red tooIf redness of the palate under the denture and burning of the tongue come together, thrush is considered. The NHS recommends taking dentures out at night and not using a denture that does not fit.
It started after antibiotics or an asthma inhalerThe NHS lists long-term antibiotic use and asthma inhalers among the conditions that make oral thrush more likely. With this history, a red, burning tongue suggests thrush.
Your mouth is constantly dryIn a dry mouth, the fungus multiplies easily and the surface of the tongue becomes smooth. The cause of the dryness, especially the medicines being taken, should be looked into separately.

When it doesn't

Numbness, tingling, balance problems or forgetfulnessThe NHS writes that B12 deficiency can affect the nervous system, and that if it is not treated some problems can become permanent. If these symptoms come with the tongue finding, see your GP without delay.
The tongue is swelling quickly, and breathing or speaking is becoming difficultCleveland Clinic defines the tongue swelling enough to affect breathing or speaking as an emergency. Call 112 without waiting.
A red area in a single place that does not moveA red area that is different from the rest of the tongue, has clear borders and has not gone in 2 weeks should be shown to a dentist or an oral and maxillofacial surgeon. The NHS lists a red patch in the mouth among the symptoms of mouth cancer.
A picture that does not improve despite treatmentCleveland Clinic recommends seeing a doctor if the symptoms last longer than 10 days or do not respond to treatment. Smoothing that continues even though the deficiency has been corrected and the thrush treated needs further assessment.
Together with diarrhoea, weight loss and abdominal painAn absorption problem coming from the bowel, for example coeliac disease or Crohn's disease, may be the cause of the deficiency. The cause needs investigating rather than settling for supplements.

The order followed to find the cause

The sequence below moves from the observation you can make at home to the doctor's assessment.

1
Look in the mirror at how the smoothing is spread
In daylight, stick your tongue out. Is the whole tongue smooth, or only the edges or the tip? Is there a white line around the smooth areas, and do they move within days? Is there a single diamond-shaped area in the middle of the tongue? Take a photo.
2
Check the rest of the mouth
Redness on the palate or under the denture; cracks at the corners of the mouth; white plaques that can be wiped off; a dry mouth. The NHS lists cracks at the corners of the mouth and a change in taste among the symptoms of oral thrush.
3
Make a list of your medicines and diet
Stomach protectors, metformin, epilepsy medicines, methotrexate, long-term antibiotics, asthma inhalers; a plant-based diet, a strict diet, regular alcohol; a past stomach or bowel operation. The NHS writes that these medicines and conditions can lower B12 or folate levels.
4
Blood test: ask for a full panel
B12, folate and ferritin in addition to a full blood count. In the study in China, B12 deficiency was much more common than anaemia (68.22% compared with 21.61%); a full blood count alone may not be enough to explain this picture. If needed, your GP will request further tests for pernicious anaemia and coeliac disease.
5
Examination by a dentist
The dentist assesses the tongue, the palate, the denture and the amount of saliva. If thrush is suspected, treatment can be started or a swab taken; if there is a sharp tooth edge or a denture that does not fit, it is corrected.
6
Treatment according to the cause, and a check-up
If a deficiency is found, supplements and an investigation of what caused the deficiency; if there is thrush, antifungal treatment; if there is dryness, its cause. The tongue is reassessed a few weeks later; if the picture has not improved, referral is made to an oral medicine specialist or an oral and maxillofacial surgeon.

Treatment routes according to the cause

The review in the American Family Physician journal writes that atrophic glossitis is often linked to a nutritional deficiency and improves once the underlying condition is treated. Treatment varies with the cause.

B12 deficiency

Supplements as tablets or injections, depending on the reason for the deficiency. In the study in China, patients with atrophic glossitis and B12 deficiency responded well to supplements. If there is an absorption problem, treatment can be long-term; the plan is made by your GP or a specialist in internal medicine.

Iron or folate deficiency

Along with supplements, the reason for the deficiency is investigated: blood loss for iron; diet, an absorption problem or medicines for folate. The NHS lists digestive diseases such as coeliac disease among the causes of folate deficiency.

Oral thrush

An oral gel available from the pharmacy or an antifungal medicine recommended by the doctor. The NHS recommends seeing a GP if there is no improvement despite 1 week of gel treatment or if swallowing is painful. For denture wearers, cleaning the denture and taking it out at night are part of the treatment.

A dry mouth

Reviewing the medicines that cause the dryness, sipping water often, and sugar-free gum that stimulates saliva. It is common for thrush to come back unless the dryness improves.

Irritation and allergy

Cleveland Clinic recommends stopping products that cause allergy, spicy food, alcohol and tobacco, and improving oral hygiene. For a sore tongue, the NHS recommends using a toothpaste without sodium lauryl sulphate and drinking cold drinks through a straw.

Mistakes commonly made with a smooth red tongue

With this complaint, the costliest mistakes are moving on to treatment without finding the cause, and settling for a single cause.

Starting B12 injections or tablets without a blood test

Values measured after supplements can hide the real situation, and the reason for the deficiency, for example pernicious anaemia or coeliac disease, can be missed. Test first, then treat.

Ending the search with a normal full blood count

The NHS writes that the symptoms of the deficiency can be seen before anaemia develops. B12, folate and ferritin should be measured separately.

Using antifungal medicine alone

Even if the thrush clears, the picture comes back if there is an underlying deficiency or a dry mouth. In the study in Japan, the fungus and a reduced flow of saliva acted together.

Thinking of nerve symptoms separately from the tongue

Tingling in the hands and feet, balance problems and forgetfulness may come from the same deficiency as the picture in the tongue. The NHS writes that the likelihood of permanent damage increases as treatment is delayed.

Wearing the denture at night too

To prevent oral thrush, the NHS recommends not wearing dentures at night and not using a denture that does not fit. The moist environment that stays constantly under the denture feeds the fungus.

How the tongue recovers after treatment

The time varies with the cause and how deep the deficiency is; the sequence below is a general framework. The plan of the doctor following you takes priority.

When irritants are stopped
When spicy, sour and hot food, alcohol and tobacco are cut down, the burning eases; this helps during the time until the cause is treated.
With thrush treatment
The NHS writes that with gel treatment improvement is expected by the end of 1 week, and that if it does not come you should see a doctor.
With treatment of the deficiency
The NHS writes that most symptoms improve with treatment. The surface of the tongue can take time to become rough again; your GP decides when to do the follow-up blood test.
The check-up examination
If the tongue does not improve even though the cause has been treated, a second cause is looked for or further assessment is carried out. Redness that persists, or continues in a single place, should be followed up.

Don't wait if

Numbness, tingling, or problems with balance or memory. See your GP without delay; B12 deficiency should be assessed quickly.
The tongue is swelling quickly, and breathing or speaking is becoming difficult. Do not wait; call 112 or go to the nearest A&E.
Swallowing is painful or difficult. With oral thrush, the NHS counts difficulty and pain when swallowing as a reason to see a doctor. See your GP.
A red area in a single place that has not gone in 2 weeks, or a sore lasting beyond 3 weeks. Show it to your dentist or an oral and maxillofacial surgeon.

What determines the cost

We do not give a single figure, because the cause behind a smooth red tongue ranges from simple thrush to an absorption disease. The items that determine it:

Scope of the tests: Full blood count, B12, folate and ferritin; if needed, tests for pernicious anaemia and coeliac disease, and a swab for thrush.
The underlying cause: A short course of antifungal treatment and long-term supplements or the treatment of a bowel disease are very different routes.
Dentures and irritation inside the mouth: Adjusting or replacing a denture that does not fit, and smoothing sharp tooth edges, may become part of the plan.

Frequently asked questions

Why is my tongue red and smooth?

When the small bumps on the surface of the tongue (papillae) disappear, the tongue looks smooth and red. The commonest causes are a lack of B12, iron or folate, oral thrush and a dry mouth; often more than one is present together.

Which vitamin deficiency causes a smooth red tongue?

Most often B12, followed by iron and folic acid. MSD Manuals also lists a lack of niacin (B3). It is a blood test, not the appearance, that tells you which one it is; B12, folate and ferritin should be measured together.

My blood count is normal. Could there still be a deficiency?

There could. The NHS writes that the symptoms of the deficiency can be seen before anaemia develops. That is why not only a full blood count but also B12, folate and ferritin should be requested.

Can thrush make the tongue red?

Yes. Thrush does not always cause white plaques; it can also appear as a red, burning, smooth tongue. The NHS writes that with thrush the inside of the mouth is red, and that when the white patches are wiped off, red spots that can bleed are left underneath.

There is a single smooth red area in the middle of my tongue

A single diamond-shaped smooth area in the back middle of the tongue may be median rhomboid glossitis; it can be linked to fungus and, if there are symptoms, improves with antifungal treatment. Even so, show a red area that persists in a single place to your dentist.

Which doctor should I see?

A GP for the blood test, and a dentist for the examination inside the mouth and the assessment of thrush and dentures. The two together give the quickest result. If the picture does not improve, an oral medicine specialist or an oral and maxillofacial surgeon assesses it.

I have started B12 supplements. When will my tongue improve?

The NHS writes that most symptoms improve with treatment, but the time varies with how deep the deficiency is. If the tongue does not improve despite supplements, a second cause such as thrush or a dry mouth should be looked for.

Is a smooth red tongue dangerous?

Most often it comes from a treatable cause. What is dangerous is the damage an accompanying B12 deficiency can do to the nervous system, and missing a red area that persists in a single place with no cause found. That is why the cause should be looked for and a picture that does not improve should be followed up.

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