Second only to the gut, the mouth is home to a diverse community of bacteria, known as the oral microbiome, with more than 700 species alone colonising our tongues, teeth and tissue.

This means the mouth acts as an early warning system for serious problems. Indeed the shape, colour and texture of your tongue can reveal whether patients are suffering from nutritional deficiencies, fungal infections and even cancer, according to experts.

'The tongue offers a remarkably accurate window into overall health,' Dr Seb Lomas a biochemist and dentist at Wonder of Wellness Clinic, Huddersfield, said. 

'Its colour, coating, and surface texture can reveal much about the oral microbiome, hydration, nutrient status, and even gut and systemic wellbeing. 

'While tongue changes alone shouldn't be used for diagnosis, they can provide valuable early clues for instance inflammation, fungal imbalance or digestive insufficiency often manifest here before other symptoms appear.' 

For centuries, traditional Chinese medicine has linked changes in the appearance of our tongue to various health conditions. 

The alternative medicine practice has long been considered controversial amongst doctors who believe it is not backed by scientific evidence.

However, growing evidence suggests that poor oral health is strongly linked to a number of serious diseases, including diabetes, dementia and even cancer.

Now leading dentists want to encourage more people to be aware of subtle changes in their mouth, such as the colour of their tongue, gum sensitivity or bad breath.

They argue that spotting these symptoms could allow patients to avoid life-changing illnesses before they begin. And it's an area of medicine that is growing increasingly advanced. 

One recent study has even shown that artificial intelligence software can analyse the colour of patients' tongues to diagnoses various health conditions including diabetes, stroke, anaemia, asthma, liver disease, and Covid-19 with 98 per cent accuracy. 

'In biological dentistry we view the mouth as a mirror to the body,' Dr Lomas said. 

'Because the oral microbiome connects directly with the gut, sinuses and airway, shifts in bacterial balance or tissue tone often correlate with broader inflammatory or metabolic changes.'

And whilst not all changes are red flags, and could simply be a sign of poor oral hygiene, certain changes may indicate more serious health concerns from yeast infections, anemia and cancer. 

Here are some of the most common tongue changes to look out for:  

A white coating could be a nasty infection

A white tongue could be a sign of a difficult-to-treat fungal infection. 

Ordinarily, the tongue should be a pinkish colour, says Dr Victoria Sampson, a London-based functional dentist . 

However, if the tongue has a white coating, this may be a sign of an oral thrush infection.

Oral thrush is an infection caused by a fungus called Candida, which can be caused by taking antibiotics over a long time, which kill off the bacteria in your mouth that usually keeps yeast in check.

People with a compromised immune system, diabetics and elderly people are more prone to this type of tongue infection — and it can also be a sign of candida overgrowth in the gut. 

But, the good news, says Dr Sampson, is that thrush can usually be treated by taking probiotic supplements - that contain so-called healthy bacteria - or by eating more fermented foods like kimchi, which boost the production of these helpful bacteria in the gut. Apples, bananas and wholegrain bread also have the same effect.

However, Dr Sampson adds that a white tongue is not always thrush. 'If you brush your tongue, and it's red and painful underneath, then that is a sign of a yeast infection,' she says.

'If you brush it and there's no redness or pain, that could be dehydration.' 

Pale tongue? You might be low in iron

When the tongue becomes very pale in colour, this is usually a sign of a nutritional deficiency, the most common of which is a lack of iron.

Also known as anaemia, the condition occurs when people don't get enough of the vital nutrient that helps transport oxygen around the body. Iron is normally found in dark green leafy vegetables, pulses, dried fruit, cereals and meat.

Anaemia is particularly prevalent among pregnant women. It can also occur as a result of serious blood loss.

Other common symptoms include tiredness and lack of energy, shortness of breath, heart palpitations, paler than usual skin and headaches. 

In the 2024 study, published in the journal Technologies, found that patients with paler tongues were highly likely to also have a lack of iron in their blood. 

As with the skin, when the tongue does not receive enough oxygen, it can appear paler than usual. 

Experts say a pale tongue could also be a sign of Raynaud's phenomenon—which occurs when blood stops flowing properly around the body— or the condition cyanosis which can cause your tongue and gums to turn a bluish-grey, as a result of poor blood circulation or a lack of oxygen in the blood. 

A bluish-grey pale tongue can be caused by serious problems with the lungs — like asthma or pneumonia. A blood clot in the heart or elsewhere in the body that is restricting blood flow can also trigger a pale tongue.

Dr Sampson added: 'The mouth is connected to the body in a number of ways, one of which is through the blood vessels.'

No need to worry about tongue bumps - unless it's also hairy

It is normal for the tongue to be covered in bumps - but there are exceptions, say experts. 

These small round bumps are called filiform, and they provide grip in order to help chew food. Normally, the tongue regularly sheds its filiforms, which are then replaced by new bumps.

However, when this doesn't happen, this allows bacteria and dirt to get trapped in the mouth.

This build-up can lead to a black, sometimes hairy-looking, tongue. The problem is more common in people with weakened immune systems, who shed their filiforms less regularly, says Dr Sampson.

She added: 'For the most part, black tongue is harmless and can be cured by practicing good oral hygiene, including brushing twice a day and using a tongue scraper to remove plaque and bacteria build up.' 

Eating more raw fruits and vegetables and staying hydrated can also help clean the tongue. 

'Overusing mouthwash, which can cause an imbalance of bacteria in the mouth, can also cause your tongue to go black,' says Dr Sampson. 

However, it can also be a sign of the virus Epstein-Barr, an infection which commonly causes glandular fever. Most people will have contracted Epstein–Barr virus, which is mainly spread through contact with saliva, by the time they reach adulthood.

Once you encounter the virus, it remains in your body. The virus can be reactivated if you have a weak immune system. When it’s active, it can trigger a hairy tongue, known as leukoplakia. 

Whilst leukoplakia isn't always something to worry about, it is typically caused by an excess growth of cells, and, left untreated, these can, in rare cases, develop into cancer. 

Deep grooves and 'scalloped' edges a sign of sleep troubles 

Marks on the edges of the tongue and grooves in its centre may be a sign of a potentially deadly sleep condition, say experts. 

'This would suggest that the tongue is pushing against the teeth during sleep,' says Dr Lomas. 'If this is the case, then it might be a sign that the airway are blocked.'

Obstructive sleep apnoea is a common sleep disorder where breathing stops and starts throughout the night. It is triggered when the muscles at the back of the throat relax, blocking off the airway.

It is strongly linked to obesity. Without treatment, sleep apnoea can lead to other more serious problems including high blood pressure, stroke, type 2 diabetes and heart disease. 

Experts say that, when the throat muscles relax, this can push the tongue forwards against the teeth. This can lead to grooves and so-called scalloped edges, where the edges of the tongue are indented and sometimes painful.

Exercising regularly, losing weight and prioritising good sleep habits can all help treat sleep apnoea.

But if these lifestyle changes do not improve the condition, then more intensive treatment options, including surgery, might be considered.

Dr Lomas said: 'These subtle signs, combined with patient history can provide important insight into breathing patterns, fatigue and overall health.'  

The warning signs of life-threatening mouth cancer   

Painless ulcers on the tongue that don't go away can be a sign of cancer, according to experts. The disease can also lead to red or white patches as well as unexplained lumps.

Mouth cancer, also called oral cancer, can affect any part of the mouth, including the gums, tongue, inside the cheeks, or lips. 

Nearly 11,000 people in the UK were diagnosed with oral cancer last year, the Mouth Cancer Foundation reports. 

The number of people diagnosed with the disease, the majority of which are men aged between 66 and 70,  has increased by more than 38 per cent over the last 20 years. 

The cancer is primarily caused by the human papillomavirus (HPV), a very common virus, typically spread through sexual contact.

Most women below the age of 30, and 18-year-old men or younger, should have received an HPV vaccine, meaning they are not at-risk. 

Mouth cancer can also be triggered by excessive smoking or drinking alcohol.

Despite growing numbers, experts say there is still relatively little awareness of the symptoms. 

Experts add this is particularly concerning as survival rates generally depend on early diagnosis and treatment. 

Since the majority of oral cancers are often caught late, only around 50 per cent of patients will survive their cancer for five or more years after their diagnosis. 

When caught early, however, more than 85 per cent of people will survive their cancer for at least five years after diagnosis.  

'If the tongue has some sort of painless ulcer that doesn't go away, that's one of the biggest warning signs of high risk oral cancer,' says Dr Sampson.

'We have to refer patients with this symptom immediately.'

Other common symptoms include pain inside the mouth, difficulty swallowing, a hoarse or croaky voice and unexplained weight loss.

Mr Mahesh Kumar, a maxillofacial surgeon and president of the Mouth Cancer Foundation, said: 'We’re increasingly seeing mouth cancer in people who don’t fit the traditional risk profile. 

'While smoking and alcohol remain major risks, the human papillomavirus (HPV) is now linked to many new cases, particularly among younger people.

'Recognising the signs early – ulcers that don’t heal, red or white patches, or unusual lumps in the mouth can make all the difference.'