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Health condition · Clinically reviewed

Mouth ulcers, why they recur - and when three weeks matters.

Most mouth ulcers are minor, painful and self-limiting. A small number are not - knowing the difference protects you.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE CKS and specialist oral medicine sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK guidance on assessment, topical treatment and the three-week referral rule.

Key facts

Mouth ulcers at a glance.

The essentials, in plain English - what it is, the types, and how it's assessed in the UK today.

  • What it is

    Recurrent, painful sores on the lining of the mouth - the most common cause of oral ulceration in the UK.

  • Minor aphthous

    The commonest type - shallow ulcers under 10mm that heal within one to two weeks without scarring.

  • Major aphthous

    Larger and deeper, sometimes over 10mm - slower to heal and can leave scarring.

  • Herpetiform

    Crops of tiny pinpoint ulcers that can merge into a single irregular, painful patch.

  • Common triggers

    Minor trauma, stress, hormonal change, and deficiency in iron, B12 or folate.

  • Three-week rule

    Any ulcer not healed within three weeks needs urgent referral to exclude mouth cancer.

Why this guide matters

Nearly always simple - occasionally, not.

Mouth ulcers are extremely common and usually harmless. The three points below shape everything else on this page.

  • Most heal on their own

    A typical minor aphthous ulcer clears within one to two weeks with simple symptom relief.

  • Recurrence points to a cause

    Ulcers that keep coming back are worth investigating - deficiency, coeliac disease and Crohn’s disease are all recognised drivers.

  • Three weeks is the line

    Any single ulcer still present after three weeks needs urgent assessment to exclude mouth cancer.

How the diagnosis is made

From first look to a clear plan.

The steps a UK GP or dentist will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History and examination

    When it started, how often it recurs, and a careful look at the site, size and edge of the ulcer.

  2. 02

    Assessing

    Classify the ulcer type

    Minor, major or herpetiform aphthous ulceration - the pattern guides the rest of the work-up.

  3. 03

    Assessing

    Ask about frequency and triggers

    Stress, hormonal timing, trauma from teeth or dentures, and any food or toothpaste pattern.

  4. 04

    Confirming

    Bloods if recurrent

    FBC and haematinics - iron, B12 and folate - are checked when ulcers keep coming back.

  5. 05

    Confirming

    Coeliac screening

    Recurrent aphthous ulceration is a recognised presentation of coeliac disease and is worth screening for.

  6. 06

    Escalating

    Urgent referral if not healing

    Any ulcer persisting beyond three weeks needs a two-week-wait referral to exclude mouth cancer.

  7. 07

    Escalating

    Specialist oral medicine review

    Major, severe or systemic-disease-associated ulceration is referred on for specialist management.

Typical timeline: most ulcers settle in one to two weeks - anything longer needs a review.

Symptoms

What mouth ulcers actually look like.

The classic mix of minor, major and herpetiform ulceration - and the features that mean it's time to get checked.

  • Minor aphthous ulcers

    Small, shallow, round or oval ulcers under 10mm - the most common type, healing in one to two weeks.

  • Major aphthous ulcers

    Larger, deeper ulcers that can exceed 10mm, take weeks to heal, and may leave scarring.

  • Herpetiform ulcers

    Multiple tiny pinpoint ulcers that can cluster and merge into one irregular, very sore patch.

  • Trauma-related ulcers

    Cheek-biting, sharp teeth or ill-fitting dentures - a mechanical trigger with a clear cause.

  • Stress and hormonal flares

    Ulcers that cluster around stressful periods or cycle with hormonal change.

  • Nutritional deficiency

    Low iron, B12 or folate is a common and treatable driver of recurrent ulceration.

  • Linked to bowel disease

    Recurrent ulcers can be an early sign of coeliac disease, Crohn’s disease or Behçet’s disease.

  • Red flag - not healed in 3 weeks

    A persistent, non-healing, firm or unusual ulcer needs urgent assessment to exclude mouth cancer.

Treatment

How mouth ulcers are treated in the UK.

Topical treatments first, correcting any deficiency next - and specialist care for major or systemic-disease-linked ulceration.

  • Topical corticosteroid

    Hydrocortisone buccal tablets or a corticosteroid paste applied directly to the ulcer reduce inflammation and shorten healing time.

  • Chlorhexidine mouthwash

    An antiseptic rinse that reduces secondary infection and can shorten the discomfort of an active ulcer.

  • Topical anaesthetic gel

    Lidocaine-based gel numbs the area, most useful applied shortly before eating or brushing teeth.

  • Choline salicylate gel

    An anti-inflammatory and analgesic gel licensed specifically for mouth ulcer pain relief.

  • Correcting a deficiency

    Iron, B12 or folate replacement where bloods confirm a deficiency - often reduces how often ulcers recur.

  • Avoiding trigger foods

    Acidic, salty, spicy or rough-textured foods can provoke or worsen flares - a food diary helps identify patterns.

  • Treating the underlying cause

    Managing coeliac disease, Crohn’s disease or Behçet’s disease directly reduces the ulcer burden that comes with them.

  • Specialist / systemic treatment

    For major or Behçet’s-associated ulceration, oral medicine may use systemic anti-inflammatory or immunomodulating treatment.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or dentist knows your history and can tell you which parts apply to you. If in doubt, get seen.

  • NICE CKS. Aphthous ulcer (recurrent).

  • NICE. Suspected cancer: recognition and referral (NG12) - oral cancer referral criteria.

  • British Society for Oral Medicine (BSOM). Guidance on recurrent oral ulceration.

  • Coeliac UK / British Society of Gastroenterology. Guidance on coeliac disease screening.

Red flags

When a mouth ulcer needs urgent attention.

Most mouth ulcers are manageable in primary care. These are the situations that aren't - and where a specialist opinion is needed.

  • Not healed within 3 weeks

    The single most important red flag - any mouth ulcer persisting this long needs an urgent 2-week-wait referral to exclude mouth cancer.

  • Firm, indurated or rolled edge

    An ulcer that feels hard at the base or has a raised, rolled border is suspicious for malignancy rather than a simple aphthous ulcer.

  • Unexplained weight loss

    Ulceration alongside weight loss should prompt a wider assessment, not just local mouth care.

  • Persistent neck lumps

    New or enlarging lymph nodes near an ulcer that won’t heal warrant the same urgent referral pathway.

  • Genital or eye involvement

    Recurrent oral ulcers together with genital ulcers or eye inflammation raise the possibility of Behçet’s disease.

  • Bloody diarrhoea or abdominal pain

    Mouth ulcers alongside gut symptoms can point to Crohn’s disease and deserve gastroenterology input.

  • Unexplained anaemia or fatigue

    Recurrent ulcers with tiredness or anaemia should prompt a check of iron, B12 and folate.

  • Smoking or heavy alcohol use

    These raise the background risk of oral cancer, so any non-healing ulcer in this group is assessed with a lower threshold.

  • Ulceration with gluten-related symptoms

    Bloating, altered bowel habit or fatigue alongside recurrent ulcers should prompt coeliac screening.

Living with it

A common condition, with a clear checklist.

Four things that make the biggest difference day to day - avoiding triggers, a gentler oral routine, timed pain relief and knowing when to escalate.

A quiet reminder

A watch that becomes a habit is easy to keep.

Noting when an ulcer started takes seconds - and it's the detail that tells you when to seek help.

  1. 01 Diet

    Avoid your triggers

    Acidic, salty, spicy or rough foods can set off a flare - a short food diary usually reveals the pattern.

  2. 02 Hygiene

    Switch your toothpaste

    Sodium lauryl sulfate (SLS) in ordinary toothpaste can worsen ulcers - an SLS-free formula and a soft brush help.

  3. 03 Comfort

    Time your pain relief

    Apply an anaesthetic gel shortly before meals so eating and drinking are more comfortable.

  4. 04 Escalate

    Watch the three-week mark

    Note when an ulcer appeared - if it hasn’t healed within three weeks, get it checked rather than waiting it out.

Frequently asked

Everything we get asked about mouth ulcers.

Quick answers on causes, treatment and when to seek urgent review.

  • What causes mouth ulcers?

    Most are minor aphthous ulcers triggered by minor trauma, stress, hormonal change or a nutritional deficiency in iron, B12 or folate. Recurrent ulcers can also be linked to coeliac disease, Crohn’s disease or Behçet’s disease.

  • What is the difference between minor, major and herpetiform ulcers?

    Minor aphthous ulcers are small, under 10mm, and heal in one to two weeks without scarring. Major aphthous ulcers are larger and deeper, take longer to heal and can scar. Herpetiform ulcers appear as multiple tiny sores that can merge into a larger, very painful patch.

  • When should I worry about a mouth ulcer?

    The main warning sign is an ulcer that hasn’t healed within three weeks - this needs an urgent two-week-wait referral to exclude mouth cancer. A firm or rolled edge, unexplained weight loss or a persistent neck lump are also reasons to seek prompt review.

  • Can mouth ulcers be a sign of another condition?

    Yes. Recurrent aphthous ulceration is a recognised feature of coeliac disease, Crohn’s disease, Behçet’s disease and nutritional deficiency in iron, B12 or folate. If ulcers keep coming back, it is worth checking for these underlying causes.

  • What treatments actually help?

    Topical corticosteroid pastes or buccal tablets, chlorhexidine mouthwash, and topical anaesthetic or choline salicylate gels are the mainstay. Correcting any nutritional deficiency and avoiding trigger foods also reduce how often ulcers recur.

  • How long should a mouth ulcer take to heal?

    A typical minor aphthous ulcer heals within one to two weeks. Major ulcers can take several weeks. Any ulcer still present after three weeks should be assessed urgently rather than left to settle on its own.

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