Most mouth ulcers are aphthous ulcers or trauma from biting, and heal on their own within 7–14 days. An ulcer needs professional examination if it lasts more than two weeks, is painless, keeps recurring in the same spot, is larger than about a centimetre, has raised or hardened edges, or comes with a lump in the neck. Painless and persistent is the combination that matters most.
The common, harmless kinds
- Traumatic ulcerFrom biting your cheek, a sharp tooth edge, a denture rubbing, or a toothbrush injury. Shape often matches the cause. Heals in about a week once the cause is removed.
- Aphthous ulcer (canker sore)Round or oval, grey-white centre with a red rim, genuinely painful out of proportion to size. Recurrent in many people. Triggered by stress, hormonal changes, certain foods, or deficiency of iron, folate or vitamin B12.
- Viral ulcersCold sores on the lip border from herpes simplex; multiple small ulcers with fever in children from primary infection. Self-limiting.
What actually helps
- Remove the cause — have a sharp tooth or an ill-fitting denture adjusted.
- Warm salt-water rinses, several times daily.
- Topical gels with a local anaesthetic or protective barrier, for eating comfort.
- Avoid acidic, spicy, salty and very hot foods while it heals.
- Consider a toothpaste without sodium lauryl sulphate if you get recurrent aphthous ulcers — some people notice a genuine reduction.
- If ulcers recur frequently, ask about iron, folate, B12 and coeliac screening.
The features that mean get it checked
- Still present after two weeks — the single most important sign.
- Painless. Harmless ulcers usually hurt; the dangerous ones often do not.
- Raised, rolled or hardened edges, or a firm feel to the surrounding tissue.
- Larger than about one centimetre.
- Recurring repeatedly in exactly the same location.
- On the side or underside of the tongue, or on the floor of the mouth.
- Accompanied by a lump in the neck, numbness, loose teeth, or difficulty swallowing.
- In anyone using tobacco, gutkha, paan masala or drinking heavily — lower your threshold considerably.
What we will do
Examine the ulcer and the whole mouth, look for a mechanical cause and remove it if present, and review after a defined interval. If it has not healed as expected, the definitive answer comes from a biopsy. Most are benign — the biopsy exists to settle the question rather than to leave it open.
Questions we get asked
Why do I keep getting mouth ulcers?
Recurrent aphthous ulceration is common and often runs in families. Stress, hormonal cycles and certain trigger foods contribute. Deficiency of iron, folate or B12 and coeliac disease are worth excluding if they are frequent.
How long should a normal mouth ulcer take to heal?
Seven to fourteen days. Anything beyond two weeks should be examined regardless of how it looks or feels.
Are mouth ulcers contagious?
Aphthous ulcers are not. Cold sores caused by herpes simplex are, particularly while blistering — avoid direct contact and sharing utensils at that stage.