Common features

• Mouth pain or burning
• Redness, swelling, tenderness
• Ulcers or blisters
• White patches or coating
• Pain with eating, drinking, or swallowing
• Drooling or reduced food/fluid intake, particularly in children

Common causes

• Viral infection: especially herpes simplex, which may cause painful blisters and ulcers with fever.
• Aphthous ulcers: recurrent small, painful “canker sores.”
• Fungal infection: oral candidiasis, often causing removable white patches.
• Irritation or allergy: spicy/hot foods, tobacco, alcohol-containing mouthwash, toothpaste flavorings, ill-fitting dentures, or chemical burns.
• Trauma: cheek biting, sharp teeth, braces, burns.
• Nutritional deficiency: iron, vitamin B12, folate, or other B-vitamin deficiency. S Das: A Manual on Clinical Surgery, pp. 1343-1354.
• Medicines or cancer treatment: chemotherapy, radiotherapy, and some drugs can cause oral mucositis/stomatitis.
• Less commonly, systemic conditions such as inflammatory bowel disease, Behçet disease, or immune-mediated blistering disorders.

What you can do initially

• Drink plenty of cool fluids; use soft, bland foods.
• Avoid acidic, spicy, salty, very hot foods, tobacco, and alcohol.
• Rinse gently with warm salt water: ½ teaspoon salt in a cup of warm water, then spit out.
• Maintain gentle oral hygiene with a soft toothbrush.
• A pharmacist or clinician can advise on a topical oral pain-relief product. The correct treatment depends on the cause, for example antifungal therapy for thrush or antiviral therapy for significant herpes infection.

Seek urgent medical care if

• You cannot drink enough, have signs of dehydration, or severe pain
• You have trouble swallowing or breathing
• There is high fever, widespread rash, eye redness/pain, or genital sores
• You are immunocompromised, receiving chemotherapy, or have uncontrolled diabetes
• An ulcer, white/red patch, or lump lasts more than 2 weeks, recurs frequently, or is associated with weight loss, neck swelling, or bleeding