Reasoning GP · Algorithm · 1-page summary
Mouth ulcers
For: adults and children with mouth ulcers in primary care. Not for: dental treatment (dentist, urgent dental service or NHS 111) or confirmed oral cancer (oncology leads).
Core rule: unexplained oral ulceration lasting more than 3 weeks, or a persistent unexplained neck lump → NICE NG12 says consider a suspected cancer pathway referral; local safety policy is to refer by default. Do not delay it with further topical treatment trials.
0Stop — call 999 now — before the full history
- Possible SJS/TEN: mouth erosions or blistering with a target or blistering rash, skin pain, fever, eye symptoms or a recent high-risk drug → stop the suspected drug → Same-day hospital (usually admission); 999 if critically unwell, airway compromise, shock or cannot travel safely. No Nikolsky testing first.
- Possible Ludwig's angina: floor-of-mouth or neck swelling with difficulty swallowing, breathing or opening the mouth, drooling or stridor → 999. No tongue depressor.
- Fever or unwell on chemotherapy or immunosuppression, or on carbimazole, clozapine or methotrexate → Immediate acute oncology / ED; no waiting for FBC.
- Unable to eat or drink (often a child with primary herpes) or systemically unwell → Same-day hospital
1Triage by duration — the 3-week rule (NG12)
| Finding | Action |
|---|---|
| <3 wk, explained | Remove the cause, treat, document; review by 3 weeks. |
| <3 wk, suspicious | Indurated, enlarging, atypical, neck lump, sore throat, dysphagia, numbness → refer now. |
| >3 wk, unexplained | NG12 “consider”; local default → Suspected cancer pathway by local route. |
| Red patch, lump | Red or red-white patch, lip or mouth lump: consider → Dentist ≤2 weeks |
| Fast-growing | Over 1–2 weeks with a hard base → cancer referral at this visit. |
2Screen — serious non-cancer causes
- Behçet's: oral plus genital ulcers, uveitis, skin lesions → rheumatology / dermatology; painful red eye or photophobia → Same-day eye
- Pemphigus / pemphigoid: widespread, skin or eye → Same-day; mouth only → Oral medicine ≤2 wk
- Syphilis: painless indurated ulcer, nodes, sexual risk → serology, Urgent GUM
- HIV: severe atypical ulcers plus risk factors → offer an HIV test.
- Methotrexate mucositis → Urgent review of dosing, renal function and FBC.
- Tonsillar asymmetry (persistent) → urgent ENT; loose teeth → OMFS.
3Assess — good light, whole mouth
☐ Site, size, base, edges, induration ☐ Lateral tongue, floor of mouth (bimanual), soft palate, retromolar ☐ Neck nodes ☐ Red or white patches ☐ Drugs, skin, eyes, genitals, gut
Tests only if adult-onset, severe, atypical or systemic features: FBC, ferritin, B12, folate, TTG IgA + total IgA (eating gluten). None for typical long-standing minor aphthae.
4Classify — only once blocks 0–2 are clear
- Minor aphthous — <1 cm, non-keratinised mucosa, heals in 7–14 days.
- Major aphthous — >1 cm, deep, 2–6 weeks; mimics cancer → oral medicine/OMFS if persistent or atypical.
- Traumatic — at a sharp tooth or denture; heals 7–10 days once removed. Not healed at 3 weeks → cancer pathway.
- Viral — primary herpes (gums, fever), hand, foot and mouth → supportive.
- Drug — nicorandil, NSAIDs, methotrexate, alendronate, chemotherapy.
- Uncertain — treat as unexplained; review by 3 weeks.
5Treat today — doses: NICE/SPC, BNF, local formulary
- Relief: analgesia, saline rinses, benzydamine 0.15% mouthwash; SLS-free toothpaste.
- Topical steroid only if the diagnosis is clear and infection excluded: hydrocortisone buccal tablets or betamethasone mouthwash (off-label, spit out). Systemic: specialist only.
- Primary herpes: consider early oral antiviral if severe, immunocompromised or poor intake.
- Nicorandil: never stop without an angina plan with the prescriber; record as an adverse reaction.
6Refer routinely
- Recurrent aphthae no better at 6–8 weeks, no deficiency → oral medicine.
- Positive TTG, or GI symptoms → gastroenterology.
- Nicorandil ulcers persisting after withdrawal → Oral medicine ≤2 wk
- Facial swelling, trismus, spreading dental infection → Same-day dental / OMFS
7Never reassure by
- Another topical treatment trial for an ulcer over 3 weeks.
- A "traumatic" label on an ulcer that has not healed.
- A non-smoker (HPV-related cancer is rising).
- Looking only at the front of the mouth.
- A normal haemoglobin: iron deficiency needs a ferritin.
- An FBC before transfer on chemotherapy.
8Safety-net — say it, then document it
999 “Call 999 for swelling under the tongue or in the neck with difficulty swallowing, breathing or opening your mouth, or drooling; or mouth blistering with a rash, skin pain or eye symptoms.” Now: “Fever on chemotherapy — acute oncology line or ED now.” Same day: “Cannot eat or drink — contact us today.” In writing: “Come back if any ulcer has not healed within 3 weeks, grows, the edge feels hard or raised, or a white or red patch won't rub off.” Track every cancer referral to an outcome.
✓Safe to leave primary care only if — all five, documented
No block 0–2 feature
Whole mouth, high-risk sites and neck nodes examined
Duration recorded; review by 3 weeks or referral made
Drug history checked; tests chosen by the criteria
Safety-net given in writing
Summary of the full Reasoning GP mouth ulcers algorithm, which holds the detail, examination, causes and evidence. Sources: NICE NG12 (updated April 2026); BSG coeliac disease guidance; NICE/UKHSA/RCGP antimicrobial prescribing summary (dental infection); current BSG/NICE iron-deficiency pathway. Clinical reference — follow local referral pathways and check doses: NICE/SPC, BNF.