General information only. This article explains dental topics in general terms and isn’t a substitute for personal advice. Everyone’s oral health and dental needs are different, so please see a dentist for advice that applies to you.
Mouth ulcers are small, painful sores inside the mouth, on the inside of the cheeks or lips, the tongue, the gums or the roof of the mouth. They are very common, and most heal by themselves within one to two weeks. Occasionally, an ulcer is a sign of something that needs attention.
Common types of mouth ulcers
- Aphthous ulcers (canker sores) are round or oval, with a white or yellow centre and a red border. They are the most common type and often recur. Most are small, but larger ones can take longer to heal.
- Traumatic ulcers are caused by injury, such as biting the cheek, a sharp tooth or filling, a rubbing denture or brace, a hot food burn or brushing too hard.
- Viral ulcers can occur with infections such as the cold sore virus or hand, foot and mouth disease. These often come with other symptoms such as a fever.
Why ulcers happen
The cause of recurrent aphthous ulcers is not fully understood. They tend to run in families, and have been associated with:
- Minor injury inside the mouth.
- Stress and tiredness.
- Hormonal changes, such as around periods.
- Low levels of iron, vitamin B12 or folate.
- Some medical conditions, such as coeliac disease and inflammatory bowel disease.
- Some medicines.
How mouth ulcers are managed
Most ulcers heal without treatment. Management usually focuses on easing discomfort while the ulcer heals, for example with soothing gels or mouth rinses, which a pharmacist or dentist can suggest. Where an ulcer is caused by a sharp tooth, filling, denture or brace, the cause can usually be smoothed or adjusted. For people who get ulcers often, a doctor may arrange blood tests to look for an underlying cause.
When an ulcer needs to be checked
An ulcer should be checked by a dentist or doctor if it:
- Has not healed within two weeks.
- Is painless, or feels hard or raised.
- Keeps coming back in the same place.
- Is unusually large or getting bigger.
- Comes with a lump in the neck, numbness, difficulty swallowing, or a red or white patch.
- Comes with fever, feeling unwell or ulcers elsewhere on the body.
An ulcer that does not heal can occasionally be a sign of oral cancer, which is why it is important to have it assessed.
Common questions
Are mouth ulcers contagious?
Aphthous ulcers and traumatic ulcers are not contagious. Ulcers caused by viruses, such as cold sores, can be passed on.
Is a mouth ulcer the same as a cold sore?
No. Cold sores are caused by a virus and usually appear on or around the lips. Aphthous ulcers occur inside the mouth and are not caused by the cold sore virus.
Why do I keep getting mouth ulcers?
Recurrent ulcers are common and often have no single cause. If they are frequent, large or slow to heal, a doctor can check for underlying causes such as low iron or vitamin levels.
Can braces or dentures cause ulcers?
Yes. Rubbing from a brace, aligner or denture can cause ulcers, particularly when it is new. A dentist can usually adjust the appliance.
When to see a dentist
See a dentist if an ulcer has not healed within two weeks, keeps returning in the same place, or seems to be caused by a sharp tooth, filling or denture. More information: smoking, vaping and your mouth.