What Are Canker Sores?
By drhemmert
March 15, 2012
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Canker Sores - What Are Canker Sores?


Many people often wonder exactly what are canker sores?

Canker sores, also known as Aphthous Ulcers, are small lesions that occur inside the mouth, and are not contagious.


One to two days before appearing, a burning or tingling sensation may be present in the area of the mouth where the lesion is developing. Rarely, a fever might present itself when developing a canker sore.
Canker sores appear inside the mouth as round or oval sores typically with a red border and yellow or white center. Canker sores typically develop:
  • On the top surface of the tongue and the tip of the tongue
  • Underneath the tongue, on the floor of the mouth
  • The inside of the cheek and lip
  • On the gum tissue

Canker sores do not develop on the external surfaces of the lips and are not to be confused with coldsores.

Types of Canker Sores

Canker sores may be classified as:

  • Minor - Although painful, minor canker sores are often fully healed within two weeks after onset. The size of a minor canker sore varies, but typically stays under 1/3 inch to 1/2 inch.
  • Major - Canker sores that appear larger that 1/3 inch to 1/2 inch, last longer than two weeks, and appear to have irregular margins -- oddly shaped -- may be classified as major. Rarely, this type of canker sore may leave behind a scar. Common in immuno-suppressed patients.
  • Herpetiform Canker Sores - A cluster of several tiny lesions that appear to form one larger sore. This type of canker sore may last from one week to one month.

Canker sores may become painful, especially when eating, drinking, and talking.


We know what canker sores are, but the exact cause is still unknown. Women statistically suffer from canker sores more often than men. Canker sores are typically seen in people between the ages of 10 and 40, although they have been known to show up at any age.

There is reason to believe that certain types of bacteria and/or viruses are responsible for the painful mouth sores. Canker sores are not contagious and are not related to the herpes simplex virus, also known as cold sores.

Canker sores are caused by:

  • Injuries to the mouth, as seen frequently by contact sports players. Accidentally biting the inside of the cheek or lip may also result in a canker sore
  • Temperature hot food or drink may cause a canker sore in the area of the mouth that was essentially burnt by the offending substance
  • Spicy and/or acidic foods often produce a canker sore as a response to the irritation these spices and acids create in the mouth
  • The use of chewing (smokeless) tobacco will often cause a canker sore to develop in the area of the mouth where the tobacco is held, due to the irritating chemicals found in the addictive product
  • Poor-fitting, complete or partial dentures may cause canker sores in the area of the mouth where the denture may rubbing on the tissue. The development of a canker sore is often one of the first signs that indicate the need for a denture reline or adjustment by your dentist
  • Orthodontic brackets, bands, and various other orthodontic attachments will often cause canker sores to develop in area of the mouth where there is constant friction on the oral tissues. This is common when orthodontic treatment first begins and may occur after each subsequent adjustments, throughout each stage of treatment
  • Allergies to metals such as nickel may become evident in the mouth of a person wearing orthodontic devices necessary to move the teeth. Canker sores may begin to appear adjacent to the metal attachments. This is often referred to as contact dermatitis.
  • Broken teeth are often sharp and may rub on the oral tissues to produce painful canker sores. Broken restorations may also cause a similar effect on the oral tissues
  • Emotional stress has been identified as a possible trigger that may cause the development of canker sores
  • Bacteria responsible for peptic ulcers known as Helicobacter pylori, has been linked to canker sore occurrence
  • Vitamin deficiencies, specifically vitamin B12, foliate (folic acid), and iron, may trigger canker sore development
  • Hormonal changes, notably during menstruation, pregnancy, and menopause, have been linked to canker sores
  • Canker sores often run in families. Genetics my be a factor for many canker sore sufferers
  • Allergic reactions and sensitivities to certain foods may cause a canker sore to develop. Allergic reaction to certain types of bacteria found in the mouth may also result in this type of mouth ulcer
  • Celiac disease sufferers may experience canker sores. Gluten may be associated with the development of canker sores in those with celiac disease
  • Information associated with inflammatory bowel disease (IBD) often will list canker sores as a complication associated with Crohn's disease and ulcerative colitis
  • Mouth sores are a common occurrence observed in immuno-suppressed patients, such as those with HIV/AIDS
  • Behcet's Disease, a rare autoimmune disease that damages the body's blood vessels notes mouth sores, more specifically canker sores, as a one of the four most common symptoms of the disease
  • Sodium lauryl sulfate is a common ingredient in toothpaste and had been associated with the development of canker sores


There are canker sore treatments and remedies that help ease pain, discomfort and possibly speed the healing process.

At-home treatment for minor canker sores include:

  • Saltwater Solution and Sodium Bicarbonate - Mix 1 teaspoon salt with one cup warm water. Swish the solution in your mouth for 30 seconds, then spit the solution out. In addition to salt, 1/2 teaspoon baking soda (sodium bicarbonate) may be added to the saline solution. Create a paste by mixing baking soda with small drops of water until a thick consistency results. Use this paste to cover the canker sores, which will help relieve pain. These methods may be repeated as often as needed. Saline and sodium bicarbonate both help the mouth heal quickly by gently reducing the alkalinity and bacteria in the mouth.
  • Hydrogen Peroxide Solution - Mix one part hydrogen peroxide with one part water. Use a cotton swab to dab the solution directly onto the canker sores. Do not swallow the solution. Hydrogen peroxide is an antiseptic that will help reduce the amount of bacteria in the mouth.
  • Milk of Magnesia - Used frequently as an aide to relieve constipation and as an antacid, milk of magnesia is a liquid suspension of magnesium hydroxide. Dab milk of magnesia directly onto the canker sores with a cotton swab, three to four times a day. This method is recommended after using the hydrogen peroxide solution. Milk of magnesia will help reduce the pain and help speed the healing process.
  • Liquid Antihistamine - Diphenhydramine (Benadryl) may be used as an oral rinse by mixing one part milk of magnesia and one part diphenhydramine together. Rinse with the solution for one minute, then fully spit out the solution. Take care to avoid swallowing this mixture.
  • Over-The-Counter Oral Care Products and Mouth Rinse - Available in most dental care sections, antiseptic mouth rinses contain ingredients intended to help heal mouth sores by reducing the amount of bacteria in the mouth. Oral care products that are manufactured to numb painful areas in the mouth are also useful when treating canker sores. Products such as gels, paste, and rinses that are specifically marketed for mouth sores may provide pain relief and help speed the healing process. It is important that you follow the manufacturers' instructions closely when using over-the-counter products.

Canker sores that are classified as major, or are considered herpetiform canker sores, may require treatment from your dentist. Common methods used to treat more serious canker sores include:

  • Oral Medications - Prescription medication may be necessary for treating serious canker sores that have developed into secondary infections. Tetracycline suspension (liquid) may be prescribed with instruction to hold the medicine in the mouth for two to five minutes before swallowing. Tetracycline is typically not prescribed for children as it has been shown to cause permanent discoloration in developing teeth. Zovirax (Acyclovir) is an antiviral drug that may be prescribed for cases where there are multiple, very painful canker sores.
  • Corticoid Steroids - Although rare, corticoid steroids such as prednisone and dexamethasone may be prescribed as a treatment for canker sores.

    Dexamethasone suspension (liquid) may be prescribed for use as an oral rinse with instruction to fully spit out after a determined time.

Keep in mind that even though they are painful, canker sores tend to heal well on their own. Consult your dentist when canker sores do not heal after 14 days, are accompanied by a fever, or appear to be infected.


A.D.A.M. "Canker Sores"

A.D.A.M. "Canker Sore Treatment"

American Dental Association. Oral Health Topics - "Mouth Sores"

Colgate World Care. Oral & Dental Health Basics - "What are Canker and Mouth Sores?"

WordNet - Princeton University Cognitive Science Laboratory - "Milk of Magnesia"

Beyond Allergy. "Allergies to Metal in the Mouth" May 8, 2007.

Herlofson BB. Barkvoll P. "Sodium lauryl sulfate and recurrent aphthous ulcers. A preliminary study." Acta Odontol Scand 1994: 52: 257-259. Oslo. ISSN 0001-6357.

NYU Langone Medical Center. "Aphthous Ulcers"