Canker sores (aphthous stomatitis) are painful white ulcers in the mouth that appear most often on the tongue, inside the cheeks, and inside the lips. Unlike cold sores, canker sores are not contagious.
The cause of canker sores is not well-understood but may include injury or irritation inside the mouth, infection, and stress. Minor canker sores heal in 1 to 3 weeks.
Most people do not need to see a doctor for canker sores. The sores will get better on their own. To relieve pain, you might try over-the-counter medicine or change your diet to bland, soft foods.