Mouth ulcers — causes and when to seek care
Reviewed By
Last Updated
October 1, 2026
When to leave it alone, when to come in, and the one rule worth remembering.
Mouth ulcers are small, painful sores in the lining of the mouth. Most are minor and heal on their own within one to two weeks. Salt-water rinses, pharmacy gels or mouthwashes and avoiding triggers help. Any ulcer lasting more than three weeks, ulcers that keep returning, or red or white patches should be checked by a dentist or GP. We assess ulcers at our Islington clinic.
Visible Signs & Symptoms
An ulcer is a break in the lining of the mouth where the surface layer has been lost. Most mouth ulcers are minor aphthous ulcers: round or oval, with a pale yellow-grey centre and a red rim, a few millimetres across. They hurt out of proportion to their size and typically resolve within seven to fourteen days without treatment.
Common signs
- One or more small, shallow sores on the inside of the cheeks or lips, on the tongue, or on the floor of the mouth.
- Stinging or soreness, particularly when eating spicy, salty or acidic food, or when brushing.
- A tingling or tender spot a day or so before the ulcer appears.
- Mild swelling of the surrounding tissue.
Different types
Minor ulcers are the most common: small, shallow and healing without a scar. Major ulcers are larger and deeper, can take several weeks to heal and occasionally leave a scar. Herpetiform ulcers appear as clusters of many pinhead-sized sores that may merge together. Ulcers caused by injury, such as a sharp tooth edge or accidental bite, usually sit where the irritation happens and settle once the cause is removed.
Who gets them
Mouth ulcers are common and can affect anyone. Recurrent minor ulcers often begin in childhood or early adulthood and tend to become less frequent with age. Many people have an occasional ulcer after biting the cheek or during a stressful few weeks; others notice a repeating pattern, with a new ulcer appearing before the last has fully healed. Keeping a simple note of when ulcers appear, where they sit, how long they last and what was happening at the time is one of the most useful things you can bring to an appointment, because it often points towards the cause.
What is not a typical ulcer
Some changes in the mouth look different from an ordinary ulcer and deserve a professional look: a sore that is not painful, a lump, a hard or raised edge, a red or white patch, or an area of numbness. Cold sores, which appear on or around the lips and are caused by a virus, are also a different condition.
Clinical Root Causes
For many people there is no single clear cause. Often several factors combine, and recurring ulcers tend to have a pattern that is worth exploring.
Local causes in the mouth
- Injury: biting the cheek or tongue, a hard toothbrush, hot food or drink, or dental treatment.
- Sharp edges: a broken tooth, a chipped filling or a rough restoration rubbing against the cheek or tongue.
- Appliances: dentures, braces, aligners or retainers that rub or no longer fit well.
- Local irritants: some people find toothpastes containing sodium lauryl sulfate associated with more frequent ulcers.
General and whole-body factors
- Nutritional deficiency: low levels of vitamin B12, iron, folate, zinc or vitamin D are associated with recurrent ulcers.
- Gut conditions: coeliac disease, Crohn's disease and ulcerative colitis can be linked with mouth ulcers.
- Hormonal triggers: some people notice ulcers around their menstrual cycle.
- Stress and disrupted sleep: a common trigger for recurrent episodes.
- Stopping smoking: some people develop ulcers for a period after quitting.
- Certain medicines: a number of medicines can cause mouth ulcers as a side effect. Do not stop a prescribed medicine without speaking to your GP or prescriber.
- Infections: some viral infections cause ulcers, particularly hand, foot and mouth disease in children.
- Autoimmune patterns: rare, but considered where ulcers are severe, frequent or accompanied by other symptoms.
Where ulcers keep returning, it is worth looking beyond the mouth. Blood tests to check for deficiencies or gut conditions are arranged through your GP, and our nutritional therapist can support diet and lifestyle alongside, not instead of, medical care.
The three rules worth remembering
Most mouth ulcers are a nuisance rather than a danger, and they heal without lasting effects. The ones that matter are the exceptions, and three simple rules cover them.
The three rules worth remembering
- The three-week rule: in line with NHS guidance, any ulcer that has not healed within three weeks should be checked promptly by a dentist or GP.
- The recurrence rule: ulcers that keep coming back suggest an underlying cause worth investigating.
- The appearance rule: anything unusual-looking, including a red or white patch, a lump or a painless sore, deserves checking.
Other reasons to be seen
- Ulcers that are unusually large, very painful, or near the back of the throat.
- An ulcer that bleeds, or becomes increasingly red and sore, which may suggest infection.
- Ulcers alongside fever, feeling generally unwell, weight loss, or sores elsewhere on the body.
- Pain that makes eating or drinking difficult, particularly in children or older adults at risk of dehydration.
- An ulcer near a sharp tooth, filling, denture or appliance that does not settle once the area is protected.
When to seek urgent help
If you have difficulty swallowing or breathing, or rapidly spreading swelling in the mouth, face or neck, seek urgent medical care through NHS 111, or call 999 in an emergency.
Being seen promptly is not a reason to worry. Most ulcers that are checked turn out to have a simple explanation, and early assessment means the cause can be dealt with sooner.
What it costs to get an ulcer looked at
Treatment depends on whether the ulcer is a one-off, has a local cause in the mouth, or keeps returning.
Self-care for a minor ulcer
- Rinse with warm salt water, or use a soft toothbrush and a mild toothpaste, ideally one without sodium lauryl sulfate.
- Avoid very spicy, salty, acidic, hard or hot food until the ulcer settles; drinking cool water through a straw can help.
- A pharmacist can advise on gels, sprays, protective pastes and antimicrobial mouthwashes that ease pain and help keep the area clean.
- Look after sleep and stress where you can, as both are common triggers.
Ulcers with a dental cause
Where a sharp tooth, broken filling or rough restoration is rubbing, we can smooth or repair it, for example with a composite filling. Where a denture, retainer or aligner is the cause, we check the fit and adjust or advise. Removing the source of irritation is usually what allows the ulcer to heal.
Recurrent or slow-healing ulcers
For ulcers that keep returning, we look for patterns in timing, site and triggers, review your medical history and medicines, and examine the mouth thoroughly. Where blood tests or prescription treatment may be needed, we write to your GP. Any ulcer that has not healed within three weeks, or any red or white patch, is referred promptly in line with NHS guidance, usually to an oral medicine or specialist service, which may include a small tissue sample. We do not carry out biopsies ourselves.
Whole-body support
Alongside medical investigation, some patients find it useful to work on diet, gut health and stress with our wellness team, including nutritional therapy with Nicoletta Peloni. This supports, rather than replaces, care from your GP.
What happens at DWL
A dental problem assessment is a focused appointment with one of our dentists to examine the ulcer, look for local causes, check the rest of the mouth, and agree next steps. If the ulcer is part of a wider picture, we will say so and help coordinate with your GP. For general self-care advice you may also find our guide on how to treat mouth ulcers useful.
Cost
- Dental problem assessment: £75
- Dental examination: £65, including a full risk assessment and a check of the soft tissues of the mouth
Any follow-up dental treatment, such as repairing a sharp tooth, is explained and priced before it goes ahead. We are a private practice and do not provide NHS treatment.
Getting here: we are at 222 Essex Road, Islington, N1, two minutes from Essex Road station on the Great Northern line. Buses 38, 56, 73, 341 and 476 stop on Essex Road, and many patients arrive by bike or Lime and Forest e-bike, with Dalston around ten minutes away. We are open Monday to Friday, 8am to 7pm, by appointment, and do not take walk-ins.
For the full picture, including how this compares with the alternatives, see our guide to emergency dentist in Islington.
Further reading
Frequently asked questions
If your question isn't here, call reception on 020 8127 4567 or book a free discovery call.Text Link
View all FAQs →When should I worry about a mouth ulcer?
When it persists beyond three weeks, when it recurs several times a month, or when it looks unusual — irregular edges, a raised or hardened border, or white or red patches nearby. A typical small, soft, round ulcer that is settling within two weeks does not need concern.
What causes recurring mouth ulcers?
Most often nutritional deficiency (B12, iron, folate, zinc, vitamin D), a gut condition such as coeliac or Crohn's, hormonal triggers, stress and poor sleep, or a local irritant like SLS toothpaste.
Can my diet really cause mouth ulcers?
Yes. Nutritional deficiency is one of the commonest causes of recurrent ulcers, and it is one of the most fixable. A blood test through your GP can identify a deficiency, and correcting it often settles the pattern.
Is it serious if an ulcer lasts more than three weeks?
It needs evaluating — that is exactly why the rule exists. Most persistent ulcers turn out to be benign, but a small minority represent something needing prompt treatment, including the rare oral cancer. The three-week rule ensures everyone gets checked rather than waiting.
Can stress cause mouth ulcers?
Yes — stress and disrupted sleep are among the most common triggers, both for single ulcers and for recurrent patterns. A high-stress stretch, a run of bad nights, or being generally run down all raise the likelihood.
How does a dentist actually help with ulcers?
We examine for a local cause — a sharp tooth, a broken restoration, a rubbing denture — and treat it where there is one. We carry out a full oral assessment to exclude the causes that must not be missed, and where a recurrent pattern suggests something systemic, we recommend blood tests through your GP.
