Mouth Ulcers
Symptoms, Causes & Treatment
Understanding mouth ulcers: what causes them, which ones need urgent assessment, and the treatments that speed healing and reduce recurrence.
What Are Mouth Ulcers?
Mouth ulcers (aphthous ulcers or canker sores) are painful breaks in the mucous membrane lining the inside of the mouth. They are extremely common, affecting approximately 20% of the population to some degree, and most people will experience at least one mouth ulcer during their lifetime.
The vast majority of mouth ulcers are benign aphthous ulcers that heal within 7–14 days without treatment. However, any ulcer that persists beyond 3 weeks, is painless, or has an unusual appearance must be assessed urgently to exclude oral cancer.
The most important rule: any mouth ulcer that has not healed after 3 weeks must be assessed by a clinician or dentist to exclude oral cancer.
What Do Mouth Ulcers Look Like?
Mouth ulcers vary in size, number, location, and associated features depending on their cause.
Painful white, yellow, or grey ulcers with red border inside mouth · Usually 2–10mm in size · Located on inner lips, cheeks, tongue, or gum margins · Painful on eating, drinking, or speaking · Heal within 1–2 weeks without treatment · May recur
Mouth ulcer persisting more than 3 weeks without healing · Ulcer that grows, bleeds, or becomes indurated · Ulcer in a smoker or heavy drinker over 40 (exclude oral cancer) · Multiple severe ulcers with systemic symptoms (possible Behçet's disease)
Any mouth ulcer not healed after 3 weeks requires urgent clinical assessment to exclude oral cancer. Painless ulcers, ulcers with raised hard edges, or ulcers in people who smoke or drink heavily are particularly concerning and should not be dismissed.
What Causes Mouth Ulcers?
Mouth ulcers have many causes. Understanding the likely cause guides appropriate investigation and management.
Aphthous ulcers (canker sores) are the most common oral mucosal disease. Minor aphthae resolve in 7–14 days; major aphthae are larger and heal in weeks. Recurrent aphthous stomatitis (RAS) affects ~20% of the population.
Mouth ulcers can be caused by iron, vitamin B12, or folate deficiency. Deficiency screening is recommended in patients with recurrent or severe aphthous stomatitis. Supplementation often reduces recurrence.
Dental caries (tooth decay) is caused by acid produced by oral bacteria (Streptococcus mutans) metabolising sugar. The acid demineralises enamel and dentine, creating cavities. Untreated cavities progress to pulpitis and then periapical abscess.
A dental abscess is a collection of pus caused by bacterial infection of the tooth pulp or periodontal tissue. It produces severe throbbing pain, facial swelling, and systemic infection. It is a dental emergency when airway involvement is suspected.
Cracked tooth syndrome causes sharp pain on biting, released on opening. Cracks may not be visible on X-ray. Temperature sensitivity is common. Severe cracks may require extraction.
Gingivitis is reversible inflammation of the gum margin caused by plaque accumulation. It is the earliest stage of periodontal disease and is completely reversible with good oral hygiene. The hallmark is bleeding on brushing.
Key Risk Factors
How Are Mouth Ulcers Assessed?
Most mouth ulcers are diagnosed clinically. Blood tests for iron, B12, folate, and coeliac screen are performed in recurrent cases. Any ulcer not healed after 3 weeks requires urgent specialist assessment to exclude malignancy.
How Are Mouth Ulcers Treated?
Most aphthous ulcers require only symptomatic relief. Persistent, recurrent, or large ulcers require specific treatment.
Supportive Measures
Rinse with warm salt water 3–4 times daily. Apply benzocaine gel for pain relief. Avoid spicy, acidic, and hard foods. Use an SLS-free toothpaste (Sensodyne True White) if toothpaste-triggered. Take paracetamol for pain.
Recurrent Mouth Ulcers
Recurrent aphthous stomatitis (RAS) significantly affects quality of life. Investigation for iron, B12, folate deficiency, and coeliac disease is essential. Treating deficiencies reduces recurrence frequency in up to 50% of cases. Topical corticosteroids, dapsone, colchicine, or thalidomide (in very severe cases) may be used for refractory cases under specialist supervision.
When Should You Seek Medical Advice for Mouth Ulcers?
An ulcer that has not healed after 3 weeks · Painless ulcer with hard or raised edges in a smoker or alcohol drinker · Ulcer associated with a neck lump. These require urgent two-week-wait referral to exclude oral cancer.
Ulcer has not healed after 3 weeks · Multiple large or very painful ulcers · You are getting frequent recurrent mouth ulcers · You are losing weight alongside recurrent ulcers.
How Can You Reduce Mouth Ulcer Recurrence?
Recurrent aphthous ulcers can often be reduced in frequency by identifying and addressing triggers.
Brush teeth twice daily with fluoride toothpaste for 2 minutes. Use interdental brushes or floss daily. This removes the plaque that causes both decay and gum disease. Electric toothbrushes are more effective than manual.
See a dentist every 6–12 months (or as recommended). Early decay is painless and cheaply treated; advanced decay requires root canal or extraction. Regular dental checks are the most cost-effective dental investment.
Do not smoke. Smoking causes periodontal disease, masks gum bleeding (a key warning sign), impairs healing after dental treatment, and is the most significant risk factor for oral cancer.
Gum disease is the primary cause of bad breath. Good oral hygiene — brushing, flossing, tongue cleaning, and regular dental hygienist visits — treats the root cause more effectively than mouthwash alone.
Wash hands before touching eyes. Do not share towels, pillowcases, or eye make-up during conjunctivitis. Viral conjunctivitis is highly contagious. Stay away from school or work until discharge has resolved.
A dental abscess with facial swelling affecting the throat, causing difficulty breathing or swallowing, is a life-threatening emergency. Call 999 immediately. Do not wait for a dental appointment.
Speak to a Clinician About Mouth Ulcers
Through The GP Service, a clinician can assess mouth ulcer symptoms, arrange blood tests, prescribe treatment, and make urgent referrals where needed.
Expert clinical advice, when you need it.
Mouth Ulcers FAQs
Minor aphthous ulcers (canker sores) are the most common type and typically heal within 7–14 days. Major aphthous ulcers are larger and take several weeks to heal. Herpetiform ulcers are multiple small clusters that coalesce. Most require no treatment beyond symptom relief.
Any mouth ulcer that has not healed after 3 weeks must be assessed by a clinician or dentist to exclude oral cancer. Painless ulcers, ulcers with hard edges, and ulcers in people who smoke or drink heavily are particularly concerning.
Topical corticosteroid gel (hydrocortisone or triamcinolone acetonide) reduces inflammation and speeds healing. Benzydamine mouthwash provides pain relief. Chlorhexidine mouthwash prevents secondary infection. Most mild ulcers require no prescription.
Recurrent aphthous stomatitis affects approximately 20% of people. Investigations should include blood tests for iron, B12, folate, and coeliac disease, as deficiencies are found in a significant proportion. Treating deficiencies often significantly reduces recurrence.
Mouth ulcers can be caused or worsened by SLS (sodium lauryl sulphate) in toothpaste, certain foods (chocolate, coffee, nuts, spicy foods), biting the cheek, and some medications (NSAIDs, beta-blockers, nicorandil). Identifying and avoiding personal triggers helps reduce recurrence.
Most common mouth ulcers are not contagious. However, ulcers caused by herpes simplex virus (herpetiform stomatitis or primary herpetic gingivostomatitis) are contagious through direct oral contact.
Behcet’s disease, Crohn’s disease, coeliac disease, and HIV can all cause recurrent or atypical oral ulceration. Mouth ulcers may be the first manifestation of these conditions.
While waiting to see a dentist, rinse with warm salt water, use over-the-counter anaesthetic gel (benzocaine), take paracetamol or ibuprofen, and avoid hot, spicy, or acidic foods and drinks.