Canker sores develop inside the mouth as small white or gray sores that have a red border. They are not contagious and may occur as one sore or several. Their exact cause is uncertain but some experts believe that immune system problems, bacteria or viruses may be involved. In some cases, trauma to the mouth’s soft tissues can cause a canker sore.
Canker sores usually heal on their own after one or two weeks. Over-the-counter topical anesthetics and antimicrobial mouthwashes may provide temporary relief. Stay away from hot, spicy or acidic foods that can irritate the sore. Antibiotics from your dentist and some oral bandages can reduce secondary infection.