Mouth ulcers are small, painful spots on the lining of the mouth, covered in white with a red edge. They are harmless, not contagious and usually heal on their own within one to two weeks. Until then, whatever spares the spot helps: a soft toothbrush, mild food and, if needed, a pain-relieving gel from the pharmacy. If a spot has not healed after two weeks, it should be checked.
Updated: 14 November 2026
- Mouth ulcers are harmless and not contagious.
- They usually heal on their own within one to two weeks.
- Not healed after two weeks: have it checked.
How to recognise a mouth ulcer
A round, flat spot, usually the size of a lentil, with a white or yellowish coating and a red edge. It sits on the inside of the lip or cheek, on the tongue or on the gum, and hurts mainly when eating, drinking and speaking.
| Type | What it looks like | Healing |
|---|---|---|
| small ulcer, the most common | the size of a lentil, up to four at a time | within one to two weeks |
| large ulcer, rare | larger and deeper, very painful | takes weeks, can leave scars |
| many very small ulcers, very rare | the size of a pinhead, all over the mouth | have it checked by a doctor |
Where mouth ulcers come from
Usually there is no clear cause. A family tendency can play a role. Known triggers are:
- small injuries, such as biting your cheek or a sharp tooth edge
- pressure from braces, a guard or a denture that does not fit well
- a deficiency, for example of vitamin B12
- certain medications
- toothpastes with sodium lauryl sulphate, a foaming agent
What helps
- Spare the spot: soft toothbrush, brush gently, but keep brushing.
- Eat mild food: spicy and sour food, hard bread and alcohol irritate the spot.
- Relieve: gels, sprays or rinses from the pharmacy ease the pain and can support healing. Better avoid mouthwashes with alcohol.
- Change toothpaste: if you often get ulcers, you can try a toothpaste without sodium lauryl sulphate.
There is no remedy that makes a mouth ulcer disappear immediately.
A spot in the mouth that has not healed after two weeks is one we look at.
Austrian public health portal gesundheit.gv.at, mouth ulcers, 2022“I keep getting mouth ulcers. Is something wrong with me?”
Usually not. Many people get mouth ulcers again and again without anything behind it. But if they come very often, it is worth having it checked, also by your GP: rarely, a deficiency or a disease of the gut or the immune system is behind it.
When you should have a spot checked
- It has not healed after two weeks.
- It is very large, or there are very many.
- The ulcers keep coming back.
- Fever, swollen lymph nodes or complaints elsewhere in the body come with it.
- A spot does not heal and does not hurt. That is exactly when it should be checked.
What we do in the practice
We look at the spot and search for a trigger in the mouth. We smooth a sharp edge on a tooth or filling, and we fix a pressure point on a guard or denture. If a spot does not heal, we arrange for further assessment.
A spot that does not heal is best shown to us soon.
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