Mouth ulcers are small, painful sores that form on the soft lining of the mouth — on the cheeks, lips, tongue, or gums. They appear as a white, yellow, or grey oval area with a red border around it.
They are very common — about 1 in 5 people in the UK gets them at some point. Most are completely harmless and heal on their own within 1–2 weeks without treatment.
There are three main types of aphthous ulcer:
Minor aphthous ulcers — the most common type. Small (under 10 mm), painful, heal without scarring in 7–14 days.
Major aphthous ulcers — larger (over 10 mm), fewer in number, much more painful, and take 2–6 weeks to heal. They can leave scarring. More likely to warrant investigation.
Herpetiform ulcers — despite the name, these are not caused by the herpes virus. They appear as clusters of many very small (1–2 mm) ulcers that can merge together. Very painful and recurrent.
These are not contagious and are not related 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 established:
Trauma — accidentally biting the inside of your cheek, a sharp food, an ill-fitting denture, or a broken tooth rubbing on soft tissue
Stress and anxiety — many people notice ulcers appearing during stressful periods
Hormonal changes — some women find ulcers coincide with their menstrual cycle
Certain foods — particularly chocolate, coffee, tomatoes, strawberries, nuts, and spicy food
Toothpaste containing sodium lauryl sulphate (SLS) — a foaming agent that can irritate some people's oral lining
Stopping smoking — some people notice an increase in ulcers when they give up smoking
Medical conditions — inflammatory bowel disease (Crohn's, coeliac), certain autoimmune conditions, and some medications can cause or worsen ulcers
Signs and symptoms
Most mouth ulcers are straightforward:
A round or oval painful sore with a white/grey centre and red rim
Soreness that is worse when eating, drinking, or brushing teeth
Usually 1–5 at a time, typically 3–10 mm in size
Heals on its own within 7–14 days
Seek prompt dental or medical advice for an ulcer that:
Has not healed after 3 weeks
Is unusually large (more than 1 cm across) or has an irregular, raised, or hardened edge
Is painless — painless ulcers are more concerning than painful ones
Keeps coming back in the same spot
Is accompanied by difficulty swallowing, a lump in the neck, or unexplained weight loss
How are mouth ulcers treated?
Most ulcers do not need treatment — they heal on their own. However, if they are painful or persistent, the following can help:
Topical anaesthetic gels or sprays (such as benzocaine gel) — these numb the area temporarily and are available from pharmacies.
Antimicrobial mouthwashes — chlorhexidine gluconate mouthwash can help prevent secondary infection and may speed healing.
Steroid lozenges or ointments (such as hydrocortisone pellets) — available on prescription or over the counter. Most effective when used at the very first sign of an ulcer developing.
Protective pastes — some products form a barrier over the ulcer to protect it from further irritation.
If a nutritional deficiency is identified, supplements (iron, B12, folate) may prevent recurrence.
What you can do at home
To ease discomfort and help healing:
Rinse with warm, slightly salty water — this is a simple, soothing rinse that keeps the area clean.
Avoid foods and drinks that sting or irritate — particularly acidic, spicy, or very hot items.
Use a soft-bristled toothbrush and take care when brushing near the ulcer.
Try SLS-free toothpaste if you get frequent ulcers — some people find this helps.
Keep a food and lifestyle diary to help identify personal triggers.
Get enough sleep and manage stress levels — both influence how frequently ulcers appear.
When to see your dentist or doctor
See your dentist or doctor if an ulcer:
Has not healed after 3 weeks — this is the most important rule
Is unusually painful, large, or keeps recurring in the same spot
Is accompanied by a skin rash, joint pain, or eye problems — these may suggest a systemic condition
Developed after starting a new medication
A persistent ulcer that does not heal must always be assessed — in rare cases it can be an early sign of oral cancer. The vast majority of ulcers are entirely 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 dentist will discuss your individual circumstances and any risks and treatment specific to you. Treatment outcomes vary between patients depending on individual circumstances.
References
Aligned with guidance from: NICE, SDCEP, FGDP(UK).