Tongue color changes
The tongue's papillae (tiny, rounded projections) may become discolored if a person smokes or chews tobacco, eats certain foods or vitamins, or has colored bacteria growing on the tongue.
Black discoloration on the top of the tongue may occur if a person takes bismuth preparations for an upset stomach. Brushing the tongue with a toothbrush or scraping it with a tongue scraper can remove such discoloration.
A small blue-black discoloration on the underside of the tongue may be a tattoo caused by a fragment of dental amalgam filling material, which contains silver, becoming stuck in the tongue.
A pale and smooth tongue can be caused by iron deficiency anemia Iron Deficiency Anemia Iron deficiency anemia results from low or depleted stores of iron, which is needed to produce red blood cells. Excessive bleeding is the most common cause. People may be weak, short of breath... read more or by pernicious anemia, which is caused by a deficiency of vitamin B12 Vitamin B12 Deficiency Vitamin B12 deficiency can occur in vegans who do not take supplements or as a result of an absorption disorder. Anemia develops, causing paleness, weakness, fatigue, and, if severe, shortness... read more .
A strawberry-red tongue may be the first sign of scarlet fever or, in a child, a sign of Kawasaki disease Kawasaki Disease Kawasaki disease causes inflammation of blood vessels throughout the body. The cause of Kawasaki disease is unknown but may be associated with an infection. Children typically have fever, rash... read more 
or multisystem inflammatory syndrome in children (MIS-C) Symptoms COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more , an uncommon complication of COVID-19.
A smooth red tongue and painful mouth may indicate general inflammation of the tongue (glossitis) or be caused by pellagra, a type of undernutrition caused by a deficiency of niacin Niacin Deficiency Niacin deficiency (causing pellagra) is uncommon in countries with low rates of food insecurity. Many people with niacin deficiency also have deficiencies of protein, riboflavin (a B vitamin)... read more 
(vitamin B3) in the diet.
Tongue surface changes
In geographic tongue, some areas of the tongue are red and smooth (like ulcers), often surrounded by a white border. Other areas, appearing white or yellow and rough, may resemble psoriasis Psoriasis Psoriasis is a chronic, recurring disease that causes one or more raised, red patches that have silvery scales and a distinct border between the patch and normal skin. A problem with the immune... read more 
or be caused by psoriasis. The areas of discoloration often move around over a period of weeks to years. The condition is usually painless, and no treatment is needed. If people have symptoms, applying low doses of corticosteroids sometimes helps.
In fissured tongue, deep grooves are located on the tongue surface. The cause is unknown, but fissured tongue may occur with geographic tongue and some other disorders. Usually, there are no symptoms and no treatment is needed.
In "hairy" tongue, keratin (a normal body protein that is in hair, skin, and nails) accumulates on the normal projections on the top of the tongue (papillae) and gives it a hairy appearance. Hairy tongue may develop when food debris is trapped in the papillae when people do not clean their mouth adequately. The tongue may also appear hairy after a fever, after antibiotic treatment, or when peroxide mouthwash is used too often.
These "hairs" on the top of the tongue should not be confused with hairy leukoplakia. Hairy leukoplakia is white, hairy-appearing patches on the side of the tongue that is caused by the Epstein-Barr virus Infectious Mononucleosis Epstein-Barr virus causes a number of diseases, including infectious mononucleosis. The virus is spread through kissing. Symptoms vary, but the most common are extreme fatigue, fever, sore throat... read more 
. It usually occurs in people with conditions that suppress the immune system, especially HIV infection Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more 
.
Strawberry tongue describes a red tongue with small "seeds." The tiny thread-like projections (papillae) on the tongue shed or slough off and the mushroom-shaped projections remain, which form the "seeds of the strawberry." Strawberry tongue may also be the first sign of scarlet fever.
SCIENCE PHOTO LIBRARY
The surface of the tongue has large, irregular patches that have the appearance of countries on a map.
Photo courtesy of Casey Campbell, DDS, MS.
Benign migratory glossitis (geographic tongue) in which the normal projections (papillae) on the tongue surface are lost and surrounded by raised white-yellow areas. The tongue also shows fissuring (deep grooves on the top and sides of the tongue), which often coexists with geographic tongue.
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The tongue is brownish and has a hairy appearance because keratin has collected on the normal projections on the top of the tongue (papillae).
Photo courtesy of Craig B. Fowler, DDS.
Whitish patches on the tongue, similar to those sometimes found inside the cheeks, may be due to
Fever
Dehydration
Thrush Noncancerous mouth growths
(a Candida infection)Leukoplakia Precancerous changes in the mouth
(a flat white spot that develops as a result of prolonged irritation)Mouth breathing
Rubbing against a sharp tooth edge or broken filling
