Canker Sore

Written by April Khan and Matthew Solan | Published on July 18, 2012
Medically Reviewed by George Krucik, MD, MBA on July 18, 2012


A canker sore (aphthous ulcer) is a mouth ulcer or sore that is open and painful. They are the most common type of mouth ulcer. Some people notice them on the inside of their lip or cheek. They are usually white or yellowish and surrounded by red, inflamed soft tissue.

A canker sore can be either a simple canker or a complex canker. A simple canker sore reemerges about three to four times every year.. This is a common type in people between the ages of 10 and 20. A complex canker sore is not as common and develops in people who have had it before.

Neither type of canker sores is contagious and usually heal on their own within a week to three weeks, although the pain normally subsides between 7 to 10 days.

Contact your physician or dentist if you develop large sores or an outbreak, or experience excruciating pain, high fever, diarrhea, rash, or headache. Also seek medical care if you are unable to drink or your canker sore hasn’t healed within three weeks.

Recognizing a Canker Sore

Signs of canker sores are:

  • smallish white or yellow oval-shaped ulcer
  • painful red area in your mouth
  • tingling sensation in your mouth

In some cases the following symptoms may also be present:

  • swollen lymph nodes
  • fever
  • not feeling well

What are the Causes and Risk Factors?

Your risk for developing canker sores increases if you are a woman or have a family history of canker sores. There are various causes for canker sores; however in some cases the cause cannot be determined. The most common causes include:

  • viral infection
  • stress
  • hormonal fluctuations
  • food allergies
  • menstrual cycle
  • vitamin or mineral deficiencies
  • immune system problems
  • mouth injury

Diagnosing Canker Sores

Your physician can often diagnose a canker sore just by looking at it. If your doctor thinks a virus, vitamin or mineral deficiency, hormonal disorder, or immune system issue is the problem, or if there is a severe breakout, he or she may order blood tests or take a biopsy of the area.

A cancerous lesion may appear as a canker sore, but will not heal without treatment.

Treating and Ridding Your Mouth of Canker Sores

Canker sores normally heal on their own. To speed up the healing avoid spicy foods, and brush and floss your teeth regularly to keep the area from becoming infected by bacteria.

Pain can be severe at times. You can lessen the discomfort several ways. For example:

  • Gargle with mouthwash or salt water. Although it will feel intense at first, it will help reduce pain.
  • Mix equal parts water and hydrogen peroxide and apply to your canker sore with a cotton swab. Repeat up to three times a day.
  • Apply milk of magnesia up to three times a day.
  • Your physician or dentist also can prescribe antimicrobial mouth rinse, antibiotics, corticosteroid ointment, or prescription mouthwash.

Tips to Prevent Canker Sores

You can prevent the recurrence of canker sores by avoiding foods that may have previously caused the outbreak. These often include spicy, salty, or acidic foods. Also, avoid foods that cause allergy symptoms, such as itchy mouth, swollen tongue, or hives.

If your canker sores pop up due to stress, adopt regular stress reduction and calming techniques, such as deep breathing and meditation.

Also, practice good oral health and use a soft toothbrush to avoid irritating your gums and soft tissue. Consult with your doctor to determine if you suffer from any specific vitamin and/or mineral deficiencies. He or she can help design a suitable diet plan or prescribe individual supplements, if needed.

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Show Sources

  • Mayo Clinic Staff. (March 24, 2012). Tests and Diagnosis. In Canker Sore. Retrieved April 2, 2012, from
  • Medline Plus. (n.d.). Canker Sore. In Health Topics. Retrieved April 2, 2012, from

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