What causes canker sores?

Herpes virus: Usually the sore starts with a tingly sensation then may feel feverish and swollen then becomes painful and you will notice a raised blister or sore with a red border. Many times they are due to a trauma or stress but the bottom line is that it is from a herpetic virus.

Several: The exact cause of most canker sores is unknown. Stress or tissue injury is thought to be the cause of simple canker sores. Certain foods -- including citrus or acidic fruits and vegetables (such as lemons, oranges, pineapples, apples, figs, tomatoes, and strawberries) -- can trigger a canker sore. Sometimes a sharp tooth surface, dental appliance, braces, or ill fitting dentures can trigger them.

Idiopathic condition: No one knows what causes canker sores. They may be caused by a virus, may be a form of allergic reaction or may result from an auto-immune condition. Nothing cures canker sores or prevents recurrence.