|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.
For a full article, see Canker sores (Aphthous ulcers).