what is a canker sore in mouth
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 or make the problem worse.. Canker sores are small, shallow ulcers that appear in the mouth and often make eating and talking uncomfortable. There are two types of canker sores 1  : Simple canker sores. 2  These may appear three or four times a year and last up to a week. 3  They typically occur in people between 10 and 20 years of age.