Smooth tongue (glossitis)

The tongue's surface is normally covered in tiny projections (papillae) that give it its rough, textured feel. When these flatten and are lost, the tongue becomes smooth, shiny, often reddened ('beefy') and frequently sore or burning — a state called atrophic glossitis. The most recognised and important causes are nutritional deficiencies: a lack of vitamin B12, folate, iron, or B vitamins such as riboflavin (B2), niacin (B3) and pyridoxine (B6) can each strip the tongue of its papillae, and a smooth sore tongue is a classic clue to B12 or iron deficiency, often alongside tiredness and other signs of anaemia. Other causes include local factors (dryness, irritation from dentures, smoking or spicy food), yeast infection, coeliac disease and other malabsorption states, some skin and autoimmune conditions, and certain medicines. Because the tongue's surface turns over quickly, it is sensitive to nutritional shortages and can be an early external sign of them. A smooth, sore tongue — especially with cracked mouth corners, tiredness, tingling in the hands and feet, or a poor or restricted diet — is therefore a useful pointer to check for a treatable deficiency.

• Vitamin B12 deficiency — a classic cause, often with tiredness and tingling.
• Folate deficiency.
• Iron deficiency — smooth sore tongue with anaemia.
• Other B vitamins — riboflavin (B2), niacin (B3), B6.
• Coeliac disease and other malabsorption — cause combined deficiencies.
• Local irritation — dentures, smoking, dryness, spicy food.
• Yeast infection, some skin/autoimmune conditions, and certain medicines.

• Vitamin B12 and folate — key deficiencies causing a smooth tongue.
• Iron studies (ferritin, iron) — for iron deficiency.
• Full blood count (with MCV) — for anaemia and its type.
• Other B vitamins (B2, B6) — where a broader deficiency is suspected.
• Coeliac testing (anti-tTG) — if malabsorption is possible.
• Examination — of the tongue and mouth, and review of diet and medicines.