Oral Health›Common problems

Mouth Ulcers: Causes, Relief and When to Get One Checked

Most mouth ulcers are harmless and heal on their own within one to two weeks. Here is what causes them, what eases the soreness, and when an ulcer that will not heal should be checked.

Updated September 2026·By the OHA editorial team·7 min read·How we write
Key takeaways
  • Mouth ulcers are common, are not contagious, and most heal on their own within about 1 to 2 weeks.
  • The most common cause is minor injury, such as biting your cheek or rubbing from a sharp tooth, a brace or a denture.
  • Soft food, avoiding spicy, salty or acidic food, a salt-water rinse and a numbing gel from a pharmacy can ease the pain.
  • Get an ulcer checked if it will not heal or keeps coming back. How long to wait varies: 3 weeks in UK advice, 2 weeks in Australian advice, and a week in American Dental Association advice.
  • Most ulcers are not serious, but one that does not heal can occasionally be a sign of mouth cancer.

A mouth ulcer is a small, painful sore inside the mouth. Better Health Channel (Victoria) describes it as the loss or erosion of part of the delicate lining of the mouth, called the mucous membrane. The NHS says mouth ulcers are common, are rarely a sign of anything serious, and should clear up on their own within a week or two.

What does a mouth ulcer look like?

healthdirect Australia describes mouth ulcers as shallow sores with a white or grey top, often red around the outside, and usually smaller than 5 millimetres across. They can appear alone or in groups, inside the lips and cheeks, on the gums, tongue or floor of the mouth. Eating, drinking, talking and brushing can make them hurt more.

Mouth ulcers are not contagious, according to the NHS and the Oral Health Foundation. The NHS says not to confuse them with cold sores, which appear on or around the lips and often start with tingling, itching or burning.

What causes mouth ulcers?

Injury to the mouth

Better Health Channel and the Oral Health Foundation say the most common cause is minor damage to the lining of the mouth, such as:

  • biting your cheek or tongue
  • a sharp or broken tooth, or a rough filling
  • braces, or dentures that do not fit well
  • brushing too hard or slipping with a toothbrush
  • sharp food, or burns from hot food or drinks

The Oral Health Foundation calls these traumatic ulcers. They are usually single and heal once the cause is removed.

Recurrent ulcers (aphthous ulcers)

Some people get ulcers again and again with no obvious injury. These are aphthous ulcers, also called canker sores. healthdirect and Better Health Channel both say about 1 in 5 people get them. The exact cause is not known, but the sources list factors that may make ulcers more likely:

  • stress, anxiety or tiredness (NHS, healthdirect)
  • hormonal changes, such as during pregnancy (NHS, healthdirect)
  • certain foods: healthdirect gives chocolate, peanuts and coffee as examples
  • low levels of iron, folate or some B vitamins; the NHS also lists zinc and vitamin D
  • some medicines: the NHS lists some anti-inflammatory painkillers (NSAIDs), beta blockers and nicorandil
  • stopping smoking, which the NHS says can bring on ulcers at first
  • toothpaste containing sodium lauryl sulphate, which the NHS advises avoiding

The sources do not agree on whether ulcers run in families. The NHS says some families get them more often, and healthdirect says about 4 in 10 people who get them have a family member who does too. The Oral Health Foundation says recurrent aphthous ulcers are not usually inherited.

Other conditions

The NHS says several ulcers at once can be a symptom of hand, foot and mouth disease, oral lichen planus (a white, lacy pattern inside the cheeks), Crohn's disease or coeliac disease (digestive conditions), or a weakened immune system. Better Health Channel also lists viral infections and autoimmune diseases.

How long do mouth ulcers last?

Most heal without treatment within 1 to 2 weeks (NHS, healthdirect, American Dental Association); Better Health Channel says 10 to 14 days. The Oral Health Foundation says less common major ulcers, which are larger and deeper, can take several weeks. healthdirect says recurrent ulcers usually become milder and less frequent over time.

What helps a mouth ulcer?

The sources differ on whether healing can be sped up. Better Health Channel says it is not possible, and that treatment manages the symptoms. The NHS says there is no quick fix, but that a pharmacist can recommend treatments to speed up healing, prevent infection or reduce pain.

Looking after your mouth

The NHS and healthdirect suggest:

  • eat soft foods, and avoid spicy, salty, acidic or rough, crunchy foods such as toast or crisps
  • avoid very hot or acidic drinks such as fruit juice, and drink cool drinks through a straw
  • brush with a soft toothbrush; healthdirect says if brushing is too painful, use a mouthwash instead, avoiding ones that contain alcohol
  • try not to touch the ulcer (healthdirect)

Salt-water rinses

All three bodies below suggest one, but their recipes differ:

  • NHS: half a teaspoon of salt in a glass of warm water, rinse and spit out, as often as you like.
  • healthdirect: one teaspoon of salt in a cup of water, held over the sore area and spat out, a few times a day.
  • Better Health Channel: warm, slightly salted water, held in the mouth for up to 4 minutes, four times a day.

Do not swallow the rinse.

Treatments from a pharmacy

The NHS says a pharmacist can recommend an antimicrobial mouthwash, a painkilling tablet, mouthwash, gel or spray, corticosteroid lozenges or a salt mouthwash. healthdirect says an anaesthetic (numbing) gel can ease the pain but will not heal the ulcer. Better Health Channel suggests an alcohol-free medicated mouthwash, preferably containing chlorhexidine, twice a day. healthdirect says vitamin B12 supplements may help an ulcer heal, but to ask your doctor first.

Treatment from a dentist or doctor

For severe, persistent or infected ulcers, the NHS says a GP or dentist may prescribe stronger treatment, such as steroids. A dentist can smooth a sharp tooth or adjust a denture (Oral Health Foundation). Better Health Channel says you may need blood tests, and occasionally a biopsy, where a small sample of tissue is taken for testing.

When should a mouth ulcer be checked?

Advice on how long to wait differs between countries:

  • UK: the NHS and the Oral Health Foundation say see a dentist or GP if an ulcer lasts longer than 3 weeks.
  • Australia: healthdirect and Better Health Channel say see a doctor or dentist if an ulcer lasts longer than 2 weeks. Better Health Channel says this matters especially if you use tobacco or drink alcohol regularly.
  • US: the American Dental Association says a dentist should examine any mouth sore that lasts a week or longer. The US National Institute of Dental and Craniofacial Research (NIDCR) says see a dentist or doctor if a sore, irritation or lump in your mouth lasts more than two weeks.

Mouth ulcers and mouth cancer

Most mouth ulcers are harmless. But the NHS says a long-lasting ulcer is sometimes a sign of mouth cancer, and Cancer Research UK says an ulcer that will not heal is a common symptom of it.

Better Health Channel adds that an ulcer caused by mouth cancer may not be sore, so a painless ulcer that does not heal still needs checking. It says tobacco and alcohol, separately and together, increase the risk of mouth cancer, and the NIDCR says most mouth cancers are related to tobacco, alcohol or both.

Keep this in proportion. The NHS says the symptoms of mouth cancer are very common and can be caused by other conditions, and Cancer Research UK says most people with these symptoms do not have mouth cancer. If it is cancer, the NHS says finding it early may make it easier to treat. See our guide to mouth cancer.

When to see a dentist
  • An ulcer has lasted longer than 3 weeks (NHS) or 2 weeks (healthdirect, Better Health Channel, NIDCR). The American Dental Association says a week or longer.
  • Your ulcers keep coming back.
  • The ulcer is different from ones you have had before, for example bigger or near the back of your throat (NHS).
  • The ulcer bleeds, or becomes more painful and red, which the NHS says may be a sign of infection.
  • You also have a red or white patch or a lump in your mouth (NHS).
  • You also have ulcers elsewhere on your body or painful, swollen joints (NHS, see a GP), or weight loss, stomach pain, a fever of 38°C or higher, or blood in your poo (healthdirect, see a doctor).

How can you prevent mouth ulcers?

Not all ulcers can be prevented, but the sources suggest brushing gently with a soft toothbrush, making sure braces and dentures fit well, eating a balanced diet, managing stress, avoiding foods that seem to trigger ulcers, and having regular dental check-ups.

Frequently asked questions

Are mouth ulcers contagious?

No. The Oral Health Foundation says they cannot be passed on by kissing or sharing cups, cutlery or food.

Can a mouth ulcer be a sign of cancer?

Occasionally. The NHS says a long-lasting ulcer is sometimes a sign of mouth cancer, but that the symptoms are very common and can have other causes. Get any ulcer that has not healed checked.

Why do I keep getting mouth ulcers?

Often there is no clear cause. Stress, hormonal changes, certain foods, low iron or vitamin levels and some medicines can play a part (see above). If they keep coming back, see a dentist or doctor.

Sources

  1. Mouth ulcers, NHS, accessed September 2026
  2. Symptoms of mouth cancer, NHS, accessed September 2026
  3. Mouth ulcers, Oral Health Foundation, accessed September 2026
  4. Mouth sores and ulcers, healthdirect Australia, accessed September 2026
  5. Mouth ulcers, Better Health Channel (Victoria), accessed September 2026
  6. Mouth sores, American Dental Association (MouthHealthy), accessed September 2026
  7. Oral cancer, NIH National Institute of Dental and Craniofacial Research, accessed September 2026
  8. Symptoms of mouth and oropharyngeal cancer, Cancer Research UK, accessed September 2026

This article is general information about oral health. It is not a diagnosis or a substitute for advice from a dentist or doctor who knows your situation. If you have pain, swelling, bleeding that does not settle, or a problem that is getting worse, see a dental professional. In an emergency, contact your local emergency service.

Toothache: Causes, Pain Relief and When to Get Help
Toothache is usually a sign that a tooth or the gum around it needs treatment. Here are the common causes, what you can safely do while you wait for a dentist, and the signs that mean you need help the same day.
Dental Abscess: Symptoms, Treatment and When It Is an Emergency
A dental abscess is a build-up of pus from an infection in a tooth or the gum. It will not go away on its own and needs a dentist. Here is how to recognise one, how it is treated and the signs that need emergency care.
Cracked, Chipped and Broken Teeth
A cracked or chipped tooth is usually not serious, but a crack cannot heal on its own and can get worse. Here are the signs, what to do straight away, how each kind of crack is treated and how to protect your teeth.