Canker sores are painful, shallow sores in the lining of the mouth. They are usually on the inside of lips, inside of cheeks, and gums. They do not cause fever.
The exact cause of canker sores is unknown. Some may result from food that gets stuck in the teeth. Others may be due to forgotten injuries from toothbrushes, toothpicks, rough foods (such as corn chips), hot foods, or biting of the lips or cheeks.
Canker sores are not the same as cold sores. The herpes simplex virus causes cold sores (also known as fever blisters) on the outer lip. This virus does not cause canker sores on the inside of the mouth.
To reduce the pain, your child can swish 1 teaspoon of liquid antacid in his or her mouth for several minutes after meals. A child over age 4 with just one ulcer can put an antacid tablet on the sore and let it dissolve. Do this 3 or 4 times a day. Give acetaminophen (Tylenol) or ibuprofen (Advil) as needed for pain (especially at bedtime).
Offer a soft, bland diet to reduce the pain. Cold drinks and milkshakes are especially good. Avoid giving your child salty foods, citrus fruits, and spicy foods. Encourage your child to drink lots of fluids to prevent dehydration. For very young children, give fluids by cup rather than from a bottle because the nipple can increase the pain.