Understanding Mouth Ulcers
Mouth ulcers are painful but usually harmless, and they heal on their own. Learn what sets them off, how to ease the pain and when to get advice.
What are mouth ulcers?
Mouth ulcers are small, painful sores inside your mouth. They form on the soft lining of the cheeks, lips, tongue or gums. They look like a white, yellow or grey oval patch with a red border.
They are very common. About 1 in 5 people in the UK get them at some point. Most are completely harmless. They heal on their own within 1–2 weeks without treatment.
There are three main types of common mouth ulcer (aphthous ulcer):
- Minor ulcers. These are the most common type. They are small (under 10 mm) and painful. They heal in 7–14 days without leaving a scar.
- Major ulcers. These are bigger (over 10 mm) and there are fewer of them. They are much more painful and take 2–6 weeks to heal. They can leave a scar. They are more likely to need checking by a professional.
- Herpetiform ulcers. Despite the name, the herpes virus does not cause them. They are clusters of many very small (1–2 mm) ulcers that can join together. They are very painful and keep coming back.
These ulcers are not catching (contagious). They are not linked to the cold sore virus.
What causes mouth ulcers?
The exact cause of common mouth ulcers is not always clear. But many triggers are well known:
- Injury. You might bite the inside of your cheek by accident. Sharp food, a denture that does not fit well, or a broken tooth rubbing your mouth can also cause them.
- Stress and anxiety. Many people get ulcers at stressful times.
- Hormone changes. Some women get ulcers at the same point in their monthly cycle (period).
- Some foods, mainly chocolate, coffee, tomatoes, strawberries, nuts and spicy food
- Toothpaste with sodium lauryl sulphate (SLS). This foaming ingredient can irritate the inside of some people's mouths.
- Low levels of some nutrients, mainly iron, vitamin B12, folic acid or zinc
- Stopping smoking. Some people get more ulcers when they give up smoking.
- Health conditions. Inflammatory bowel disease (Crohn's, coeliac) and some autoimmune conditions can cause ulcers or make them worse. So can some medicines.
Signs and symptoms
Most mouth ulcers are simple:
- A round or oval painful sore with a white or grey centre and a red edge
- Soreness that is worse when you eat, drink or brush your teeth
- Usually 1–5 at a time, often 3–10 mm across
- Heals on its own within 7–14 days
Get dental or medical advice soon for an ulcer that:
- Has not healed after 3 weeks
- Is very large (more than 1 cm across), or has an uneven, raised or hard edge
- Is painless. Painless ulcers are more worrying than painful ones.
- Keeps coming back in the same place
- Comes with trouble swallowing, a lump in the neck, or weight loss you cannot explain
How are mouth ulcers treated?
Most ulcers do not need treatment. They heal on their own. But if they are painful or do not go away, these can help:
- Numbing gels or sprays (such as benzocaine gel). These numb the area for a short time. You can buy them from a pharmacy.
- Germ-killing mouthwash. Chlorhexidine gluconate mouthwash can help stop the ulcer getting infected. It may help it heal faster.
- Steroid lozenges or ointments (such as hydrocortisone pellets). You can get these on prescription or buy them. They work best if you use them as soon as you feel an ulcer starting.
- Protective pastes. Some products cover the ulcer to protect it from more irritation.
- If tests show you are low in a nutrient, supplements (iron, B12, folate) may stop ulcers coming back.
What you can do at home
To ease pain and help healing:
- Rinse with warm, slightly salty water. This simple, soothing rinse keeps the area clean.
- Avoid food and drinks that sting, mainly acidic, spicy or very hot things.
- Use a soft toothbrush. Take care when you brush near the ulcer.
- If you get ulcers often, try an SLS-free toothpaste. Some people find this helps.
- Keep a food and lifestyle diary to help find your own triggers.
- Get enough sleep and manage stress. Both affect how often ulcers appear.
When to see your dental team or doctor
See your dental team or doctor if an ulcer:
- Has not healed after 3 weeks. This is the most important rule.
- Is very painful or large, or keeps coming back in the same place
- Comes with a skin rash, joint pain or eye problems. These may be signs of a condition that affects the whole body.
- Started after you began a new medicine
An ulcer that does not heal must always be checked. In rare cases, it can be an early sign of mouth cancer. Most ulcers are completely harmless, but it is always better to get it checked.
This leaflet is for general information only and does not replace professional dental advice. Your dental team will discuss your individual circumstances and any risks and treatment specific to you. Treatment outcomes vary between patients depending on individual circumstances.
Sources
- Mouth ulcers. NHS website (nhs.uk), reviewed March 2024.
- Suspected cancer: recognition and referral (NG12). National Institute for Health and Care Excellence (NICE), 2015, updated April 2026.
- Management of Acute Dental Problems, 2nd edition. Scottish Dental Clinical Effectiveness Programme (SDCEP), 2026.
Links checked 18 October 2026.
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