Sore inside corner of mouth
A sore at the inner corner of the mouth may come from trauma, an ulcer, infection, or dryness, so its appearance and duration matter.
The short answer
A sore at the inner corner of the mouth may be a traumatic ulcer, irritation from a tooth or appliance, angular cheilitis, or another lesion, so its appearance and duration matter. The mouth corner and nearby cheek should be examined if it does not settle.
How do ulcers and corner-of-mouth inflammation differ?
An ulcer is a break in the moist lining of the mouth, while angular cheilitis affects the skin folds at the lip corners and may cause cracking or crusting. A sharp tooth edge, cheek biting, dry lips, saliva pooling, yeast, or bacterial irritation can produce similar soreness.
What can you do while a sore at the mouth corner heals?
Rinse gently with water or mild salt water, keep the area clean, and avoid spicy or acidic foods while it heals. Do not pick the sore; a dentist can smooth a sharp tooth, adjust an appliance, or prescribe treatment when an infection or persistent ulcer is found.
When does a sore inside the mouth corner need examination?
Arrange an examination for a sore that lasts, returns often, enlarges, hardens, bleeds without provocation, or is associated with a neck lump or difficulty swallowing. Sudden facial swelling with breathing difficulty requires urgent care.
What should you ask about the exact site of this mouth sore?
Ask whether the lesion is on the lip skin, the inner cheek, or the gum and what feature identifies its likely cause. Ask whether a sharp edge, appliance, dry mouth, yeast, or another condition needs treatment or follow-up.
Frequently asked questions
Can a sharp tooth cause this sore?
Yes, repeated rubbing or cheek biting can injure the lining and keep an ulcer open.
Can I put household products on it?
Avoid caustic products and use gentle rinsing until the cause is identified.
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.