Canker sores are shallow, painful sores in your mouth. They are usually red. Sometimes they have a white coating over them. You might get them on the inside of your lips, the insides of your cheeks or under your tongue. Canker sores are different from fever blisters, which usually are on the outside of your lips or the corners of your mouth.

Anyone can get canker sores, but people in their teens and 20s get them more often. Canker sores may run in families, but they aren't contagious. Doctors don't know what causes canker sores.

What should I do when I get canker sores?

If you have small canker sores you can treat them at home. You can try taking ibuprofen (brand name: Advil) or acetaminophen (brand name: Tylenol) for pain. Two other medicines called Orabase and Zilactin-B might keep your canker sores from becoming irritated by eating, drinking or brushing your teeth. You put these medicines right on the sore.

You can also mix equal amounts of Milk of Magnesia and Benadryl Allergy liquid. After it's mixed, you can swish a teaspoonful in your mouth for about one minute and then spit it out. If you do this every 4 to 6 hours, your canker sores may hurt less.

When should I call my family doctor about canker sores?

If your canker sores are large, last longer than a week or are so sore that you can't eat, you should make an appointment to see your doctor. You should make an appointment with your doctor, too, if you also have a fever or feel sick when you have canker sores.

What can my doctor do to help my canker sores?

Several prescription medicines may help with canker sores. You can talk about them with your doctor.

What's the right way to use the medicine for my canker sores?

You may be asked to “swish and swallow” the medicine. This means that you swish the medicine around in your mouth, especially around your canker sore, for a few minutes before swallowing it.

If your doctor has you use a medicine to put on the canker sore, you should dry the sore with a tissue. Next, put a small amount of medicine on a cotton swab (like a Q-Tip). Then, put the medicine on your canker sore using the cotton swab. Don't eat or drink for 30 minutes. If you do, the medicine will be washed away. Be sure to use the medicine for as many days as your doctor tells you to.