Why is my tongue bright red?

A healthy tongue is pink and slightly rough from thousands of tiny papillae. When it turns red, the shape of the redness gives the best clue to the cause:

• Smooth, glossy and red all over (sometimes called a "beefy" red tongue): the papillae have thinned. MedlinePlus explains that when the tongue is inflamed, papillae are lost and the tongue looks smooth. This pattern points toward nutritional causes.
• Red and bumpy, like a strawberry: the papillae are swollen and prominent. This is typical of some infections and inflammatory illnesses, especially in children.
• Red patches with a pale or white border that move around: usually geographic tongue, which is harmless.
• One red patch that stays put: needs a professional look, because a persistent red area can be erythroplakia.

Vitamin and mineral deficiencies

MedlinePlus lists folic acid and vitamin B12 deficiency, pernicious anemia, pellagra (lack of niacin, vitamin B3), sprue and Plummer-Vinson syndrome among the causes of a red tongue. The NHS lists "a sore or red tongue, sometimes with mouth ulcers" as a symptom of B12 or folate deficiency anemia, alongside tiredness, shortness of breath, headaches and, with B12, pins and needles. Iron deficiency can also make the tongue sore. The NHS lists people at higher risk: vegans who do not take B12 supplements or fortified foods, people who regularly drink heavily, people with absorption problems such as celiac disease, and people taking medicines such as proton pump inhibitors or metformin.

Irritation and minor injury

Burning the tongue on hot food or drink, or a lot of spicy, acidic or sour food, can leave it red and tender for a few days. The NHS notes that a burned or bitten tongue usually settles within days.

Allergic reactions

Cleveland Clinic lists allergic reactions to foods, medicines or dental products among the causes of glossitis. A new toothpaste, mouthwash or medicine shortly before the redness is a useful clue.

Infections

Viral, bacterial and fungal infections can all inflame the tongue. Oral thrush, for example, can leave the mouth red inside with white patches, according to the NHS.

Geographic tongue

Smooth red patches with a white or light border that change shape over days or weeks. It is harmless and not linked to cancer. Our geographic tongue guide explains it in detail.

A red, bumpy "strawberry" tongue in a child with fever deserves attention the same day.

• Scarlet fever starts like flu, with a high temperature, sore throat and swollen neck glands. The NHS describes a white coating on the tongue that peels away, leaving it red and swollen with small bumps, and a rough, sandpaper-like rash 12 to 48 hours after the first symptoms. It is treated with antibiotics, so contact a doctor.
• Kawasaki disease mainly affects children under 5. The NHS says the main symptom is a high temperature lasting 5 days or more, with redness inside the mouth and on the tongue, red eyes, cracked lips, rash and swollen hands or feet. It needs urgent assessment because it can affect the heart.

The MSD Manual also lists multisystem inflammatory syndrome in children (MIS-C), an uncommon complication of COVID-19, as a cause of strawberry tongue.

• Go gentle on the tongue. Use a soft toothbrush and skip scraping while the tongue is sore; scraping an inflamed surface only irritates it.
• Avoid triggers for a week: very hot drinks, spicy and acidic foods, alcohol, tobacco and strong mouthwashes. The NHS also suggests toothpaste without sodium lauryl sulphate.
• Stop any new oral product you started just before the redness, such as a new toothpaste or rinse.
• Do not start high-dose supplements on a guess. A simple blood test can show whether B12, folate or iron is low, and the right treatment depends on the cause.

Treatment follows the cause. A doctor may order blood tests for anemia, B12, folate and iron, and treat a deficiency with supplements or, for pernicious anemia, B12 injections. Infections are treated with the appropriate antibiotic or antifungal. Allergic glossitis improves once the trigger is removed. A dentist will examine any fixed red patch and may take a biopsy, since the MSD Manual notes that persistent red areas in the mouth may be a sign of mouth cancer.

Cleveland Clinic advises contacting a provider if glossitis symptoms last longer than 10 days or do not respond to treatment, and calling 911 if the tongue swells enough to affect breathing or speaking. See a dentist for any single red patch that lasts more than two weeks, even if it does not hurt.