CANKER SORES - Dr. Lara Coseo

Canker sores are a painful, and sometimes disruptive, problem in the mouth. They can affect your ability to eat, drink, and speak. While much remains unknown about them, this article will detail the things we do know.

What are Canker Sores?

The scientific name for canker sores is aphthous ulcers, or for short aphthae. An aphthous ulcer consists of a round or oval ulceration that is white in color, surrounded by a ring of bright red tissue. These painful ulcers form on the unattached gingiva inside the mouth (the gum tissue that is not attached to the underlying jawbone but instead can move freely). This includes the inside of cheeks and lips, the tongue and floor of the mouth, and the soft palate. It does not include the hard palate or gum tissues attached to the bone over tooth roots.

The size, severity, and duration of these sores depends on their classification. Aphthous ulcers come in three varieties: minor, major, and herpetiform.

Minor Aphthous Ulcers

Minor aphthous ulcers are the most common type of canker sores. These ulcers range from 5 to 10 millimeters in diameter, and they resolve themselves within approximately 10 to 14 days. Many people do not seek treatment from their dentist for minor ulcers, instead opting to simply let them run their course.

Major Aphthous Ulcers

Major aphthous ulcers are less common (only about 10-15% of all canker sores), and much more painful. These larger sores have a diameter greater than a centimeter (they can be dime or nickel-sized). They penetrate deeper into the tissues with the potential to leave scars. They also last much longer, up to several months. 

Due to their size, depth and duration, these ulcers cause significant pain and disruption of everyday life. This leads most affected people to seek treatment for some type of pain relief.

Herpetiform Aphthous Ulcers

Herpetiform aphthae are less common, and they have a significantly different appearance from the other types. The name herpetiform describes their appearance, which mimics that of intraoral herpes lesions caused by HSV-1. (This is the virus that causes cold sores or fever blisters. It is not the sexually transmitted form of herpes.)

The appearance of both herpetiform aphthae and intraoral HSV lesions is a cluster of many tiny ulcers, which are 1-2 millimeters in size. The important distinction between the two is in theirlocations. Your dentist can quickly tell you which you have when he or she sees where the sores are located inside your mouth.

Herpetiform aphthous ulcers typically last 7-14 days. In some cases, the tiny ulcerations may coalesce to form one large ulcer, which can be quite painful.

What Causes Canker Sores?

Scientists have not uncovered a single cause of canker sores. There are many suggested predisposing factors in the literature, and we’ll cover most of those here. People who consistently suffer from canker sores can usually find a pattern in their lives to know when they are at highest risk.

- Trauma

Many people develop canker sores in an area that has been injured or traumatized. Something as simple as biting your lip during a meal can lead to a painful ulcer. Often, people can experience ulcers in response to a sharp edge on a tooth or dental appliance that irritates an area of the soft tissue inside the mouth.

- Nutritional Deficiencies

Studies have shown a correlation between an increased prevalence of aphthous ulcers and certain vitamin and/or mineral deficiencies. When your body does not have enough vitamin B12, zinc, iron, folic acid among others, you are more likely to develop canker sores. If you suffer from frequent canker sores without trauma in the area, you should ask your medical doctor to check for nutritional deficiencies!

- Allergic Reactions

Allergic reactions to dental materials are relatively rare, but they do occur. When some has a true allergy to a retainer, nightguard, partial or denture, they may develop ulcers in multiple areas of the mouth. Some people have allergies to ingredients in oral care products, like toothpastes and mouthwashes.

- Severe Dry Mouth

Patients who suffer from chronic, severe dry mouth have a much higher risk for developing painful mouth sores. Without the lubrication of saliva, the soft tissues of the mouth undergo constant frictional irritation from the teeth. Patients with dry mouth are also more likely to bite their lips, cheeks and tongue, which can lead to ulcers as well.

- Health Problems

Various systemic health conditions are associated with an increased prevalence of canker sores. These include HIV, Behcet’s disease, and Celiac disease among many others. The mechanism isunknown, but scientists suspect that a depressed immune system caused by various health conditions puts you at a higher risk for ulcers in your mouth.

- Stress

Researchers cannot determine the mechanism through which psychological stress causes aphthous ulcers, but they have found a definite correlation in increased stress levels with increased ulcer prevalence. Those who suffer from repeated canker sores can attest to the fact that they tend to occur during periods of high stress levels.

How Can You Prevent Canker Sores?

Because the specific causes of canker sores remain vague, preventing them can be difficult. In general, the most important weapons in fighting aphthous ulcers will be protecting the soft tissues from trauma and maintaining a healthy immune system.

This may involve something as simple as chewing more slowly so that you reduce your risk of biting your cheeks, lips, and tongue. You can also wear protective mouthguards during sleep or athletic activity.

Another important method of protecting the soft tissues inside the mouth is ensuring adequate lubrication. In cases of dry mouth where natural lubrication is missing, you can use an artificial lubricant, such as Biotene’s dry mouth gel.


In order to support a healthy immune system, you should drink plenty of water to maintain good hydration and eat a balanced low-sugar diet. Ideally, you should get the vitamins and minerals you need through your food, but if that is not possible, you can add a multivitamin supplement to your daily routine.

People who are prone to canker sores should also use mild, hypoallergenic oral care products. The ingredient most commonly associated with irritation inside the mouth is Sodium Lauryl Sulfate (or SLS). This detergent is responsible for the foaming action of most toothpastes. Look for one that is SLS-free if your mouth is sensitive or prone to sores. 

What Treatment is Available for Canker Sores?

The treatment for aphthous ulcers varies widely among healthcare providers. Some doctors will prescribe oral steroids to fight inflammation and promote healing of the sores. Steroid creams and ointments are available to treat intraoral sores, but their effectiveness is reduced by their inability to stay in place because they are easily washed away by saliva.

A prescription mouthwash containing an antihistamine, a topical anesthetic, and a coating agent (usually an antacid like Milk of Magnesia). This mouthwash can help patients manage the pain of ulcers while they heal. This treatment is particularly helpful when the underlying cause of the sore is a true allergy to something in the mouth.Your medical doctor may place you on vitamin and/or mineral supplements if he or she diagnoses a deficiency. This therapy may not speed up the healing process of the current ulcer, but it should reduce your risk for future sores.

Many dental offices provide laser therapy to reduce inflammation and improve the healing of aphthous ulcers.


--- By Dr. Lara I She is a 2004 graduate of Baylor College of Dentistry. She practiced general dentistry for 13 years before retiring for medical reasons. She currently serves as an Adjunct Associate Professor at Texas A&M College of Dentistry.

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