Bite the inside of your cheek and a round white sore appears that stings with every meal. The NHS says mouth ulcers should clear up on their own within a week or 2; there is no quick fix, but a soft-bristled toothbrush, cool drinks through a straw and softer foods make the wait easier. If one lasts longer than 3 weeks, it says to see a dentist or GP. This sets out the NHS page “Mouth ulcers”.
1. Usually gone in a week or 2. They need time; there is no quick fix.
2. Avoid very spicy, salty or acidic food, crunchy food and very hot drinks. Cool drinks through a straw.
3. Get it checked if it lasts over 3 weeks, looks different, or bleeds and turns red. A long-lasting ulcer is sometimes a sign of mouth cancer, the page says.
What they are — NHS
The NHS says mouth ulcers usually appear inside the mouth on the cheeks or lips, and its example photo shows a large, white, circular ulcer inside the bottom lip. It is clear on one point: mouth ulcers are not contagious and should not be confused with cold sores. Cold sores are caused by a virus and can spread, so they are a different matter (cold sores).
While it heals — NHS
| Type | What the NHS says | Worth noting (our gloss) |
|---|---|---|
| Do | Use a soft-bristled toothbrush | Less contact with the sore |
| Do | Drink cool drinks through a straw | Keeps the drink off the ulcer |
| Do | Eat softer foods | — |
| Do | Regular dental check-ups · a healthy, balanced diet | Where causes like a sharp tooth get spotted |
| Don’t | Eat very spicy, salty or acidic food | — |
| Don’t | Eat rough, crunchy food such as toast or crisps | — |
| Don’t | Drink very hot or acidic drinks such as fruit juice | — |
| Don’t | Use toothpaste containing sodium lauryl sulphate | Check the ingredients list |
How to brush in the first place is in brushing for 2 minutes.
Why they happen — NHS
The NHS says a single ulcer is usually caused by something you can avoid: biting the inside of your cheek, badly fitting dentures or braces, rough fillings or a sharp tooth. Harder-to-control causes include hormonal changes such as during pregnancy, some medicines, vitamin deficiencies and stopping smoking. It may be surprising that quitting smoking can bring on ulcers, but the NHS lists it among the causes.
Several ulcers can be linked to conditions such as hand, foot and mouth disease, oral lichen planus, Crohn’s disease, coeliac disease, HIV or lupus. If you also have ulcers elsewhere on your body, or painful, red, swollen joints, see a GP.
At the pharmacy — NHS
A pharmacist can recommend a treatment to speed up healing, prevent infection or reduce pain, the NHS says. Options available without a prescription include antimicrobial mouthwash, painkillers, corticosteroid lozenges and salt (saline) mouthwash. We haven’t matched product names sold in Korea, so ask a pharmacist.
When to see a dentist or GP — NHS
| When | Where | Worth noting (our gloss) |
|---|---|---|
| It lasts longer than 3 weeks | Dentist or GP | A week past the usual 1 to 2 |
| It is different from past ulcers (bigger, near the back of the throat) | Dentist or GP | — |
| It bleeds or becomes more painful and red | Dentist or GP | May be a sign of infection |
| Ulcers elsewhere on the body · painful, red, swollen joints | GP | The “several ulcers” causes |
The NHS files these as non-urgent. It also says most mouth ulcers are harmless, but a long-lasting ulcer is sometimes a sign of mouth cancer, so it’s best to get it checked. Where to go is covered in ER vs local clinic.
Checklist
- ☐ Give it a week or 2 — soft toothbrush, soft food
- ☐ Skip spicy, salty, acidic, crunchy food and very hot drinks
- ☐ Check your toothpaste ingredients
- ☐ Same spot again and again? Ask a dentist about a sharp tooth or dentures
- ☐ Over 3 weeks: dentist or GP
Questions that remain
Will vitamins make it heal faster?
The NHS lists vitamin deficiency as one cause, but doesn’t say vitamins speed healing. “There is no quick fix” is what this page says.
Can I catch a mouth ulcer?
The NHS says mouth ulcers are not contagious. Cold sores, which blister around the lips, are a different thing.
If the tooth itself hurts rather than an ulcer, the NHS has separate toothache advice — a salt-water rinse is half a teaspoon in a glass of water (toothache).
The NHS has separate advice on bad breath — gum disease and holes in teeth are common causes, and see a dentist if it hasn’t gone after a few weeks (bad breath).
Sources
- NHS — Mouth ulcers — source (page shows: reviewed 11 March 2024, next review 11 March 2027; checked 12 October 2026). A week or 2, not contagious, 5 dos and 4 don’ts, causes, 4 pharmacy options, dentist and GP list, 3 weeks, mouth cancer.
- Not read. Korean agency guidance on mouth ulcers; Korean product classifications.
- What we added. The “worth noting” column.
Where else to check
- A pharmacist — mouthwashes and lozenges.
- A dentist — sharp teeth and dentures.
Written on 12 October 2026. The content is from the NHS; the glosses are ours.