Mouth Ulcers (Aphthous Stomatitis) — Causes, Types & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Mouth ulcers (aphthous ulcers or canker sores) are painful shallow erosions of the oral mucosa that affect approximately 20% of the population recurrently — recurrent aphthous stomatitis (RAS) is the most common oral mucosal disease. Three clinical subtypes are recognised: minor aphthae (80% of RAS — ulcers under 10 mm, healing in 7-14 days without scarring); major aphthae (Sutton's disease — 10% — ulcers over 10 mm, lasting 6 weeks or longer, healing with scarring); and herpetiform aphthae (10% — clusters of 5-100 small (1-3 mm) punctate ulcers resembling herpetic lesions but not caused by HSV, healing in 7-30 days). Most mouth ulcers are idiopathic or triggered by local trauma or stress. However, recurrent or persistent mouth ulcers may be a manifestation of serious systemic conditions: inflammatory bowel disease (Crohn's disease — mouth ulcers in up to 20%; orofacial granulomatosis), coeliac disease, Behcet's disease (oral plus genital ulcers plus uveitis), nutritional deficiencies (iron, B12, folate), HIV, lupus, and reactive arthritis.

Recurrent aphthous stomatitis is multifactorial. Genetic predisposition: family history in 40% of patients — if both parents have RAS, 90% of children develop it. Local trauma: sharp foods (crisps, toast crusts), ill-fitting dentures, cheek biting, toothbrush abrasion. Stress (psychological and physical) — consistently identified trigger in prospective studies. Sodium lauryl sulphate (SLS) in toothpaste: an anionic surfactant that disrupts oral mucin and may promote ulceration — SLS-free toothpaste reduces RAS frequency in some patients. Hormonal changes: perimenstrual exacerbation in some women. Nutritional deficiencies: iron, vitamin B12, folate, and zinc deficiency are found in 20% of RAS patients — correction may reduce recurrence. Food triggers: acidic foods (citrus, tomatoes, vinegar, pineapple), gluten (in undiagnosed coeliac disease), nuts, chocolate, and coffee are variably reported. Medications causing aphthous-like oral ulcers: nicorandil (a potassium channel activator for angina — causes large, painful, treatment-resistant ulcers), NSAIDs, gold, methotrexate, and antiviral medications. Systemic disease: Crohn's disease (deep fissuring ulcers with cobblestone appearance, lip swelling — orofacial granulomatosis), Behcet's disease, MAGIC syndrome, and HIV (atypical large or necrotising aphthae in immunosuppressed patients).

Minor aphthae: round or oval, 2-10 mm ulcers with a white or grey fibrinous base (pseudomembrane) surrounded by a distinct erythematous (red) halo; located on non-keratinised mucosa — buccal (inner cheek) and labial (inner lip) mucosa, ventral tongue, floor of mouth, and soft palate; very rarely on the gingiva, hard palate, or dorsal tongue (which are keratinised). Pain is typically disproportionate to ulcer size — significantly impairs eating, drinking, swallowing, and speech. Prodrome: a tingling or burning sensation may precede ulcer appearance by 24-48 hours. Frequency in RAS: 1-3 episodes per month typical; some patients describe continuous ulceration ('revolving door RAS'). Major aphthae: over 10 mm, very painful, can persist for weeks to months, located on any oral mucosa including the soft palate and oropharynx; heal with scarring, causing trismus if perioral. Herpetiform aphthae: multiple tiny discrete ulcers that may coalesce into an irregular large ulcer — often on the ventral tongue and floor of mouth; very painful; may last 30 days.

Mouth ulcer diagnosis is primarily clinical — based on history (onset, duration, frequency, triggers, associated symptoms), appearance (morphology, number, distribution), and medical/medication history. Blood tests for recurrent aphthae (to exclude systemic causes and deficiencies): full blood count (anaemia, macrocytosis); ferritin, serum iron, TIBC (iron deficiency); vitamin B12 and folate; zinc; anti-TTG antibody and total IgA (coeliac disease — the most commonly missed cause); consider HIV test if risk factors present. Biopsy: for ulcers persisting over 3 weeks without healing, large major aphthae, or atypical features (irregular border, indurated base, cervical lymphadenopathy) — to exclude malignancy (oral squamous cell carcinoma can present as a non-healing ulcer). Oral cancer red flags requiring urgent 2-week wait biopsy referral: unexplained ulcer lasting over 3 weeks; unexplained lump in the mouth; unexplained red or white patch in the mouth; unexplained hoarseness lasting over 3 weeks. Systemic investigation: if Behcet's disease suspected — pathergy test, ophthalmology, rheumatology review; if Crohn's suspected — colonoscopy with biopsies; if SLE — ANA, anti-dsDNA, complement.

The goal of treatment is pain relief, accelerated healing, and prevention of recurrence. Mild RAS (infrequent, small, minor aphthae): chlorhexidine gluconate 0.2% mouthwash (antiseptic — reduces secondary bacterial colonisation and may slightly accelerate healing); benzocaine or lidocaine gel (topical anaesthetic — provides immediate pain relief before meals); carmellose sodium paste (orabase — forms a protective film over the ulcer); avoid identified triggers; SLS-free toothpaste; correct nutritional deficiencies (ferrous sulfate, B12, folic acid). Moderate RAS: topical corticosteroids — the most effective pharmacological treatment; triamcinolone acetonide 0.1% in orabase paste (applied to the ulcer 2-4 times daily); betamethasone sodium phosphate 500 mcg dissolved in water as a mouthwash (use for 3 minutes, spit, and rinse — do not swallow); prednisolone 5 mg tablet dissolved in 10 mL water as a mouthwash (for widespread aphthae); fluticasone propionate MDI inhaler used intraorally. Adjunct: tetracycline mouthwash (250 mg capsule dissolved in water — antibacterial; significantly reduces pain and ulcer duration in RAS; do not swallow; contraindicated in children under 12). Severe/major aphthae: systemic corticosteroids (prednisolone 20-40 mg daily — short course, taper); colchicine 0.5-1.5 mg daily (used as steroid-sparing, anti-inflammatory); dapsone; thalidomide (highly effective for HIV-associated aphthae and Behcet's — requires specialist supervision and pregnancy prevention due to severe teratogenicity). Nicorandil-associated ulcers: stop nicorandil (switch to an alternative anti-anginal agent) — ulcers heal within 2-4 weeks of discontinuation.

Major aphthae (Sutton's disease) cause severe, protracted pain lasting 6 weeks or longer, with healing producing visible intraoral scarring that may cause restricted mouth opening (trismus), difficulty swallowing, and permanent mucosal deformity — particularly when multiple major aphthae occur simultaneously or recurrently. Repeated ulceration at the same site creates mucosal scarring and may cause partial closure of the pharynx or oesophagus in severe Behcet's disease. In immunosuppressed patients (HIV, organ transplant recipients on immunosuppressive therapy), aphthae can become large, deep, necrotising, and coalesce — causing severe dysphagia, weight loss, and oral feeding failure. Delayed diagnosis of the systemic cause: unrecognised coeliac disease (presenting as recurrent aphthae with anaemia) allows ongoing intestinal damage and malabsorption; unrecognised Behcet's disease may cause sight-threatening uveitis or life-threatening vascular complications. Any oral ulcer persisting beyond 3 weeks without healing requires urgent biopsy to exclude oral squamous cell carcinoma.

Switch to SLS-free toothpaste: sodium lauryl sulphate disrupts the protective oral mucin layer and has been shown in RCTs to reduce RAS frequency by 50% in some patients. Avoid identified dietary triggers: keep a food diary and eliminate acidic foods (citrus, vinegar, tomatoes), nuts, chocolate, and spicy foods if these consistently precede ulcer episodes. Correct nutritional deficiencies: patients with RAS should have iron, B12, folate, and zinc levels checked and deficiencies corrected — this alone eliminates recurrent aphthae in some patients, particularly those with undiagnosed coeliac disease (a strict gluten-free diet resolves aphthae). Protect oral mucosa from trauma: use a soft-bristled toothbrush; smooth down sharp tooth edges or ill-fitting denture flanges; avoid hard or sharp foods. Stress management: mindfulness, CBT, and sleep hygiene reduce stress-triggered episodes. Perimenstrual exacerbation: some women benefit from a progesterone oral contraceptive pill, which stabilises hormonal fluctuations that trigger RAS. For recurrent severe RAS: prophylactic colchicine or continuous topical corticosteroid use may be considered under specialist supervision.

See a dentist or GP urgently for any oral ulcer that does not heal within 3 weeks — this requires referral for urgent biopsy under the 2-week wait cancer pathway to exclude oral squamous cell carcinoma, which can present as a painless or mildly painful non-healing ulcer. See a GP for: recurrent mouth ulcers occurring more than 3 times per year; ulcers associated with genital ulcers or eye inflammation (possible Behcet's disease — specialist referral needed); mouth ulcers with unexplained weight loss, chronic diarrhoea, or abdominal pain (possible Crohn's disease or coeliac disease); very painful large ulcers (major aphthae) lasting over 4 weeks; or mouth ulcers in an immunosuppressed patient. Speak to a doctor about stopping nicorandil if you have recurrent painful oral ulcers and take this medication — nicorandil is a specific and under-recognised cause that resolves completely on drug withdrawal.