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Mouth ulcers

Also called Aphthous ulcers or Canker sores

Mouth ulcers are painful sores that appear inside the mouth, usually round or oval and white, red, yellow or grey. They are common and usually heal on their own within 1 to 2 weeks. Causes include biting the cheek, sharp teeth, stress, hormonal changes and some foods. Sometimes they are linked to conditions such as coeliac disease or Crohn's disease.

Last updated Nov 9, 2026

What it is

Mouthwashes, gels and pain-relieving sprays can help while they heal.

A mouth ulcer that lasts more than 3 weeks should be checked by a dentist or doctor.

Common signs

  • Round or oval sores inside the mouth
  • Pain when eating, drinking or brushing
  • Swelling around the sore

How it is usually diagnosed

  • Examination of the mouth
  • Blood tests if they keep coming back

Records worth keeping

Keeping these together makes each appointment easier, especially when you see a new doctor:

  • Notes on how often ulcers appear
  • Blood test results

Questions to ask your doctor

  • Why do my ulcers keep coming back?
  • Should I be tested for any conditions?
  • Which treatment would help?

When to get help right away

Call 112 or go to the nearest emergency department if you have:

  • A mouth ulcer that does not heal in 3 weeks, or ulcers with fever and feeling very unwell: get it checked soon

This page is general information. It is not a diagnosis and does not replace a doctor who knows your history. Medfold keeps your records organised; it does not interpret them.

Sources

Related conditions

Mouth cancerCancer of the mouth, tongue, lips or gums. A mouth ulcer or lump that does not heal in 3 weeks should be checked.Coeliac diseaseAn autoimmune condition in which eating gluten damages the lining of the small bowel. It is treated with a lifelong gluten-free diet.Crohn's diseaseA lifelong condition in which parts of the digestive system become inflamed, causing flare-ups of diarrhoea, tummy pain and tiredness.