Canker sores, referred to as recurrent aphthous stomatitis, are the most common oral ulceration.  They affect approximately 20% of the population and are most common in younger individuals.  Canker sores are considerably less common in people over 50 years of age.  What causes a canker sore?  There are several immunological processes that likely cause a canker sore to appear.  Nutritional and metabolic factors can contribute to their development.  The common predisposing factors are nutritional deficiencies, certain medications, chemical irritants, and hormonal changes.  A canker sore appears as a painful, inflamed, round ulceration.  They can often be diagnosed by simple examination.  The primary goals in managing a canker sore is to provide pain relief, shorten the length of each episode, and to try to decrease the frequency of recurrence.  Topical therapy is usually the best treatment, by targeting the canker sore directly.  Over-the-counter remedies and topical anesthetics are typically adequate for pain management.