What causes canker sores?

Canker sores, also called aphthous ulcers, are small, shallow lesions that develop on the soft tissues inside the mouth in areas like the lip, tongue, cheek, or at the base of the gums. Canker sores are usually white or yellow and are often surrounded by red, inflamed soft tissue. Canker sores can be painful, and interfere with eating. In rare or severe cases of canker sores, individuals could experience fever, physical fatigue, or swollen lymph nodes.

Canker sores come in two types: simple or complex. Complex canker sores are less common and occur mostly in people who have had canker sores in the past. Simple canker sores can occur three to four times per year and last up to a week or two. Unlike cold sores, canker sores are not contagious, no matter the type.

Causes of Canker Sores  

The exact cause of most canker sores is unknown, but there are some specific situations where outbreaks have been known to occur. Physical or emotional stress is likely to increase a person's chances of getting canker sores. Tissue injury to the inside of the mouth is also a probable cause of simple canker sores. Acidic foods like fruits, tomatoes, eggplant, and gluten can trigger an outbreak as well. Dentures and braces that don't properly fit can also cause injury, creating canker sores.

Some complex canker sores may be a sign of underlying health conditions like a weakened immune system, dietary conditions and vitamin deficiencies, or gastrointestinal tract diseases.

While most canker sores typically go away on their own within a week, sometimes they may require medical attention from your doctor or dentist. You should consult a doctor or dentist if canker sores:

• become larger or more painful
• recur with frequent outbreaks
• last more than two weeks
• cause extreme difficulty eating or drinking
• are accompanied by a high fever.