A coated or white tongue occurs when the surface is colonised by bacteria or fungi, and dead cells become trapped between the small nodules on the tongue.
A coated tongue isn't a disease and isn't usually a sign of anything serious. It's usually only temporary.
You can try gently brushing it with a tongue scraper and drinking plenty of water to help it improve.
However, sometimes a coated tongue can indicate an infection or more serious condition. You should see your GP for advice if:
You can read on to learn more about the possible causes of a coated tongue, but don't use this to diagnose yourself with a condition – always leave that to your GP.
Note that in a minority of people, a coated tongue may never return to its normal colour or texture, even after treatment.
Leukoplakia is a common condition that results in a white patch in the mouth, which sometimes appears on the tongue. The patch is usually painless but cannot be removed by brushing or scraping.
This white patch seems to be the result of too many cells being produced from the lining of the mouth and a protein called keratin being deposited. Leukoplakia can develop when the tongue has been irritated, and is linked with drinking too much alcohol and also with smoking.
Although not usually dangerous, in a few cases leukoplakia turns cancerous, often many years or even decades after it first appears.
It's important that your mouth is regularly examined by a dentist or doctor to ensure any leukoplakia isn't increasing in size or changing, or that new areas of leukoplakia are not developing.
Read more information about leukoplakia.
Your dentist or specialist will usually be able to tell the difference between a white tongue caused by leukoplakia and a coated tongue.
Oral lichen planus (lichen planus of the mouth) is a long-term disorder of the immune system that causes white lacy streaks and white patches in the mouth, including on the tongue.
Mild cases do not usually cause any pain or discomfort, although it can cause burning sensations and discomfort in the mouth, painful red gums and sore patches in the lining of the mouth.
The exact cause of oral lichen planus is unknown. It doesn't run in families and can't be passed on to other people.
Mild cases will not need any treatment. More severe cases can be managed with an antiseptic mouthwash plus steroid sprays or steroid tablets dissolved in water to make a mouth rinse.
Read more information about lichen planus.
Oral thrush is a yeast infection in the mouth caused by a fungus. It can cause a burning sensation on the tongue as well as sore white plaques that can be scraped off (although it may sometimes appear as a red patch).
You are more likely to develop oral thrush if you:
You should see your GP if you think you have oral thrush. If it's left untreated, the symptoms will persist and your mouth will continue to be uncomfortable. Treatment is with antifungal medicines.
Read more information about oral thrush.
Syphilis is a bacterial infection usually caught by having sex with someone who is infected.
Syphilis can cause a small painless sore or ulcer on the tongue if caught from having oral sex. This appears from 10 days to three months after exposure to the infection. Treatment is with a single dose of penicillin.
If left untreated, syphilis may lead to white plaques on the tongue called syphilitic leukoplakia.
Read more information about syphilis.