Canker sores are painful shallow ulcers (sores) in the lining of the mouth, usually on the inside of lips, inside of cheeks, and gums. You will not have a fever with a canker sore.
The exact cause of canker sores is not known. Some may result from prolonged contact with 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 self-biting.
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.
The white color of canker sores is the normal color of healing tissue in the mouth. They clear up in 1 to 2 weeks. Once they begin, no treatment can speed up the healing.
To reduce the pain, swish 1 teaspoon of an antacid solution in your mouth for several minutes. For a single sore, put an antacid tablet on the sore and let it dissolve. Do this 3 or 4 times a day. Take acetaminophen (Tylenol) or ibuprofen (Advil) as needed for pain (especially at bedtime).
Eat a soft, bland diet to reduce the pain. Cold drinks and milkshakes are especially good. Avoid salty foods, citrus fruits, and spicy foods. Drink a lot of fluids to prevent dehydration.
Canker sores tend to recur in some people. Good attention to toothbrushing and flossing after meals may prevent some sores. Be careful with toothpicks and rough foods.
Try to identify any foods that might be causing the ulcers. Were tomato, citrus fruit, peppermint, cinnamon, nuts, or shellfish eaten within the last day? If you find a food that you think may be causing the problem, don't eat the food for 2 weeks and then eat it again to see whether you get canker sores from it. If the canker sores do come back, try to avoid that food in the future.
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