Canker Sores

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Canker Sores

Topic Overview

What is a canker sore?

A canker sore is a shallow sore shaped like a crater (ulcer) on your tongue or on the inside of your lip or cheek. Canker sores have a red border and a white or yellow centre. They may be painful and can make it hard to talk and eat. You may have one or more than one canker sore at a time. Unlike cold sores, you cannot spread canker sores to other people. See a picture of canker sores.

Anyone can get a canker sore but women, teenagers, and young adults have them more often. People usually get their first canker sore between the ages of 10 and 40. Most people have canker sores at some time in their lives, and some people have them regularly.

What causes a canker sore?

The cause of canker sores is unknown, but they tend to run in families. Canker sores may also develop when you:

  • Are stressed or tired.
  • Have your menstrual cycle, if you are a woman.
  • Hurt your mouth, such as biting your lip.
  • Have braces on your teeth.
  • Have food allergies. Eating foods that you are allergic to may cause you to get a canker sore.
  • Eat or drink food or juice that has a lot of acid, such as orange juice.
  • Do not get enough vitamins or minerals in your diet, such as iron.

What are the symptoms?

The main symptom of a canker sore is getting a shallow ulcer on your tongue or on the inside of your lip or cheek. The sore may be large or small, and it will have a red border and a white or yellow centre. You might have more than one canker sore at a time.

Canker sores usually begin with a burning or tingling feeling. They may be swollen and painful. Having a canker sore can make it hard to talk or eat.

Canker sores may hurt for 7 to 10 days. Minor canker sores heal completely in 1 to 3 weeks, but major canker sores can take up to 6 weeks to heal. Some people get another canker sore after the first sore has healed. Most canker sores heal without a scar.

How is a canker sore diagnosed?

If you see your doctor or dentist about the pain caused by your canker sores, he or she will do a physical examination by looking in your mouth to diagnose the canker sores.

How is it treated?

You do not need to see a doctor for most canker sores. They will get better on their own. There are many things you can try at home to relieve the pain caused by your canker sores:

  • Eat soft, bland foods that are easy to swallow, such as yogourt or cream soup. Cut your food into small pieces or mash or puree it. Avoid coffee, chocolate, spicy or salty foods, citrus fruits or juices, nuts, seeds, and tomatoes.
  • Drink cold fluids, such as water or iced tea, or eat Popsicles. Sometimes fluid touching the canker sore can cause a stinging pain. Use a straw so the fluid doesn't touch the canker sore. Hold ice on the canker sore until it is numb.
  • Rinse your mouth with salt water. To make a salt water rinse, dissolve 1 tsp (5 g) of salt in 1 cup (250 mL) of warm water.
  • Buy an over-the-counter medicine such as Orabase, Anbesol, or milk of magnesia to put on your canker sores. Use a cotton swab to apply the medicine. Put it on your sores 3 to 4 times a day.
  • Take a pain reliever, such as non-steroidal anti-inflammatory drugs (NSAIDs), including ASA, ibuprofen (such as Advil), or naproxen (such as Aleve). Do not give ASA to anyone younger than 20 because of the risk of Reye syndrome.

If your canker sores do not feel better after trying these steps at home for 2 weeks, you may need to see your doctor or dentist. He or she may recommend medicines that will help the pain caused by your canker sores. Usually these medicines are swished or gargled in your mouth, or they are painted on the sore. Your doctor may prescribe steroid cream (triamcinolone or fluocinonide) to rub on your canker sore and/or a prescription mouthwash to use.

Talk to your doctor if you have a fever, have trouble swallowing, or if your canker sores keep coming back. You may have another problem that is causing your symptoms.

How can canker sores be prevented?

Most of the time the cause of canker sores is unknown. Unless you know what causes your canker sores, you cannot prevent them from happening. If you do know what causes your canker sores, you can help prevent them by avoiding what you know causes them. For example, if you have gotten canker sores in the past from hurting the inside of your mouth, you might help prevent them by chewing your food slowly and carefully, trying not to talk and chew at the same time, and using a soft-bristled toothbrush when you brush your teeth.

If you have gotten canker sores in the past by eating foods that have a lot of acid (such as citrus fruits or tomatoes) and sharp or harsh foods (such as bread crusts, corn chips, or potato chips), it might help to avoid these. Other ways that might help to prevent canker sores include limiting your use of alcohol and tobacco and controlling the stress in your life.

In general, it is important to get enough vitamins and minerals in your diet, like folic acid, vitamin B12, zinc, and iron.

Other Places To Get Help


American Dental Association
211 East Chicago Avenue
Chicago, IL  60611-2678
Phone: (312) 440-2500
Web Address:

The American Dental Association (ADA), the professional membership organization of practicing dentists, provides information about oral health care for children and adults. The ADA can also help you find a dentist in your area.


Other Works Consulted

  • Allen CM (2009). Aphthous ulceration (canker sore) section of Diseases of the mouth. In RE Rakel, ET Bope, eds., Conn's Current Therapy 2009, p. 850. Philadelphia: Saunders Elsevier.
  • Beaudreau RW (2004). Soft tissue lesions of the oral cavity section of Oral and dental emergencies. In JE Tintinalli et al., eds., Emergency Medicine: A Comprehensive Study Guide, 6th ed., pp. 1486–1487. New York: McGraw-Hill.
  • Blair EA, Eibling DE (2001). Systemic, autoimmune, and allergic conditions section of Mucosal lesions of the oral cavity, tongue, and oropharynx. In KH Calhoun et al., eds., Expert Guide to Otolaryngology, pp. 240–246. Philadelphia: American College of Physicians.
  • Bruch JM, Treister NS (2010). Aphthous stomatitis (canker sores). In Clinical Oral Medicine and Pathology, pp. 53–56. New York: Humana Press-Springer.
  • Lustig LR, Schindler J (2010). Intraoral ulcerative lesions section of Ear, nose, and throat. In SJ McPhee, MA Papadakis, eds., Current Medical Diagnosis and Treatment 2010, 49th ed., p. 203. New York: McGraw-Hill Medical.
  • Quinn KL (2010). Management of patients with oral and esophageal disorders. In SC Smeltzer et al., eds., Brunner and Suddarth's Textbook of Medical-Surgical Nursing, 12th ed., pp. 999–1000. Philadelphia: Lippincott Williams and Wilkins.


By Healthwise Staff
Primary Medical Reviewer Kathleen Romito, MD - Family Medicine
Primary Medical Reviewer Brian D. O'Brien, MD - Internal Medicine
Specialist Medical Reviewer Arden Christen, DDS, MSD, MA, FACD - Dentistry
Last Revised November 19, 2010

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