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, stress, inheritable conditions, and female hormones. The sores usually heal in 7 to 10 days.

There is no specific cure for canker sores, but home treatment often relieves the discomfort.