Open your mouth and stick out your tongue. It may show if you have a serious disease.

This practice is usual examination in traditional Chinese medicine.

Illnesses have been diagnosed by the tongue’s appearance for millennia, one reason being that people used to be too embarrassed to undress in front of a doctor.

This has changed, of course, but to this day, even mainstream Western physicians make use of tongue diagnosis.

The tongue is closely linked to the brain and other internal organs via nerve pathways, so when something in the body is amiss, the tongue shows it.

The agile appendage reflects a person’s state of health, says Dr Dirk Esser, medical superintendent of the Department of Otolaryngology at Erfurt Helios Hospital in Germany.

Normally, the tongue is a pale pink colour, with a somewhat rough surface and slight coating. A tongue that looks much different from that, even for a few hours, could be a sign of illness.

If it’s black more than periodically, leukaemia may be to blame, while a strong, constant, yellow discolouration could indicate liver or gallbladder problems.

A brown tongue points to possible digestive tract trouble, a greyish one to anaemia, and a blue one to lung disease.

A cold or gastrointestinal disorder often gives the tongue a thick, white coating.

“The biochemical processes in the body behind tongue colouration haven’t yet been scientifically explained,” remarks Rene Graeber, a traditional practitioner in Germany.

He says acid levels in the body could play a role. If an illness causes an imbalance of bile – a yellowish-brown alkaline fluid that’s stored in the gallbladder and aids in digesting fat – acid levels are disrupted as well.

“This could explain a yellow tongue coating, which is linked to the gallbladder,” Graeber says.

The colour of your tongue may be a good indicator of your health.

A study in 2015 found that changes in the formation and breakdown of amino acids could play a role in a brownish tongue coating in cases of gastritis.

Discolouration isn’t the only way the tongue indicates health problems. “Smooth tongue”, known medically as atrophic glossitis, is marked by a smooth, glossy appearance of the muscular organ.

“This occurs due to deficiencies of vitamins or minerals,” notes Dr Andreas Filippi, an oral and dental implant surgeon at the University Centre for Dentistry in Basel, Switzerland.

A burning sensation or inflammation of the tongue could also be a sign of a vitamin deficiency.

If it’s continually red, called “raspberry tongue” or “strawberry tongue”, scarlet fever is a likely cause.

Coating on just one side of the tongue may be due to a nerve disorder or middle ear infection.

A swollen, brown-tinged tongue could be a sign of kidney failure.

And “geographic tongue”, characterised by uneven patches resembling smooth red islands, indicates a digestive tract disorder, Graeber says.

A temporary tongue coating or discolouration is generally no cause for concern, however. Eating blueberries, for example, will turn the tongue blue for a while.

Dr Esser advises everyone to regularly check the appearance of his or her tongue at home in front of a mirror, preferably in daylight and immediately after getting up in the morning – before the tongue has been coloured by food or beverages.

If something appears abnormal, he says, it should be addressed during a visit to one’s family doctor.

Sometimes, the tongue is infected with a fungus. This typically happens to people with a weakened immune system or during therapy with antibiotics.

Oral thrush, as the infection is called, can be treated with antifungal lozenges. Some over-the-counter mouthwashes may help too, Dr Esser says.

Dr Filippi recommends cleaning the tongue regularly, “ideally with a tongue brush and not a tongue scraper”.

Since most of the bacteria in the mouth are on the tongue, cleaning it helps to prevent tooth decay and bad breath. The tongue brush should be used with a special paste or toothpaste.

Graeber has another tongue-cleaning tip – oil pulling, in which you swish around in your mouth a mixture of one teaspoon each of coconut oil and sesame seed oil.

“This doesn’t harm the oral flora and helps guard against infections in the mouth,” he said. – dpa