Aphthous ulcer

An aphthous ulcer, commonly called a canker sore, is a small, painful, shallow sore on the soft lining of the mouth, such as the inner cheeks, lips or tongue.

The ulcers are round or oval with a white or yellow center and a red border, and they are not contagious, which distinguishes them from cold sores caused by the herpes virus. Most heal on their own within one to two weeks. Triggers can include minor mouth injuries, stress, hormonal changes, certain foods and deficiencies of iron, folate or vitamin B12, and some people experience recurrent outbreaks.

A dentist or physician diagnoses them by appearance and history; persistent, unusually large or frequent ulcers may prompt blood tests to look for underlying conditions. Topical cannabidiol has been evaluated in small clinical studies of canker sores, and the results await replication in larger trials.