Definition of Ulcer, aphthous

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Ulcer, aphthous: A small sensitive painful ulcer crater in the lining of the mouth. Commonly called a canker sore.

Picture of a canker sore

Aphthous ulcers are one of the most common problems that occur in the mouth. About 20% of the population (1 in 5 people) have aphthous ulcers at any given time. Aphthous ulcers typically last for 10-14 days and they heal without leaving a scar. There are many possible causes of aphthous ulcers. Often the cause is unknown.