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The main symptom you'll notice with canker sores is that your mouth gets very tender on and around the sores. How bad the pain is will depend on where the sores are, and how many you have.

You may find that eating or talking makes the pain worse. If it's really bad, you might try to avoid eating or talking altogether. If you often have difficulty eating because of canker sores, you need to be careful not to lose too much weight.

If your canker sores keep coming back, or if you have a sore that takes more than a week to heal, your dentist or doctor should take a look.¹

Your dentist or doctor will examine your mouth and ask you:²

• How often you get canker sores
• How quickly they go away
• If anything seems to trigger them or make them worse
• Whether you can eat when you get them and, if not, whether you've lost weight as a result.

You probably won't have any other symptoms. If you do, it could be a sign that you have an infection or another condition that is causing the canker sores. Tell your doctor if you also have a fever, an upset stomach or sores anywhere else on your body.¹

Doctors don't usually do any tests for canker sores. But if your doctor thinks you might not have enough iron in your blood, you might have a blood test.²

If your doctor or dentist thinks your sores might be caused by another illness, you will be referred to see a specialist. For more information about other causes, read What else could it be?

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.