A canker sore appears as a round white spot with a red border. That's what canker sores are like for people who experience them. These shallow ulcers in your mouth can make eating and talking uncomfortable. They may occur on your tongue, on your soft palate, inside your cheeks or lips, and at the base of your gums.

Canker sores differ from cold sores in that they occur in the soft tissues of your mouth and aren't contagious. Conversely, cold sores rarely develop in the soft tissues of your mouth and are extremely contagious because they're caused by the herpes virus.

Canker sores are common, but the cause in many cases is unknown. Canker sores can occur at any age, but often first appear when you are between 10 and 40 years of age.

Often, treatment isn't necessary. Pain often decreases after several days, and canker sores usually heal within one to three weeks. Occasionally, severe canker sores can develop that are larger than 1 centimeter in diameter or last longer than two weeks or both. 

Treatment 

Often treatment isn't necessary and your canker sore will heal on its own. Your doctor may suggest prescription medication if your sores are large, painful or persistent. To relieve the pain and irritation of canker sores, your doctor may recommend a prescription mouthwash, a corticosteroid salve or an anesthetic solution.

Because canker sores can recur, you may be able to reduce their frequency by addressing factors that seem to trigger canker sores:

• Watch what you eat. Avoid foods that seem to irritate your mouth. These may include acidic foods, nuts and certain spices.

• Don't chew and talk at the same time. You could cause minor trauma to the delicate lining of your mouth, triggering a canker sore.

• Follow good oral hygiene habits. Regular brushing after meals and flossing once a day can keep your mouth clean and free of foods that might trigger a sore. Using a soft brush may help you avoid irritation of mouth tissues.