Canker sore inside the mouth
A canker sore is a shallow, painful ulcer on movable mouth lining that usually heals without a dental procedure.
The short answer
A canker sore is a small ulcer of the oral mucosa, often with a pale centre and red border, that can hurt while eating or speaking. It usually affects non-keratinised lining such as the inner lip, cheek, or underside of the tongue.
What can trigger a canker sore inside the mouth?
A minor injury, stress, illness, hormonal change, or nutritional problem may precede an ulcer, although the exact trigger is often unclear. A cold sore is different because it typically begins as grouped blisters on the lip edge.
How can you ease discomfort while a mouth ulcer heals?
Rinse gently with salt water, choose soft cool foods, and avoid spicy, acidic, or rough foods while the ulcer heals. A pharmacist or dentist can recommend a topical treatment when pain interferes with eating.
When should a mouth ulcer be examined by a dentist?
Arrange an examination if an ulcer is unusually large, recurrent, spreading, associated with fever, or not healing. A persistent or firm ulcer needs assessment to exclude trauma, infection, immune disease, or another oral lesion.
How can a dentist distinguish a canker sore from other lesions?
Ask whether the lesion is a canker sore, traumatic ulcer, cold sore, or another condition, and whether a sharp tooth or appliance is rubbing it. Ask what treatment can reduce pain and how recurrence should be evaluated.
Frequently asked questions
Is a canker sore contagious?
A canker sore is not spread by ordinary contact, unlike an active cold sore caused by herpes viruses.
Can a sharp tooth cause a mouth ulcer?
Yes. Repeated rubbing from a tooth, filling, denture, or appliance can produce a traumatic ulcer that needs removal of the irritant.
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Who wrote this page
This library is published by Dental Nation, a licensed dental group practising in the United Arab Emirates. Pages are written and overseen by the same clinical team that treats patients in our clinics, and are held to a fixed editorial standard for safety and accuracy.
This page is patient education, not medical advice, and cannot replace an examination. Anything urgent — facial swelling, trauma, uncontrolled bleeding or severe pain — needs a dentist or emergency care now.