What is aphthous ulcer?

Canker sore.: An aphthous ulcer is also known as a canker sore, often a painful circular lesion inside the mouth. It does not have one specific cause, but it can be brought on by many triggers such as stress, infection, vitamin deficiencies, or immune system abnormalities. Other than being painful, they are harmless and can be treated with topical oral agents.

Canker sores: Aphthous ulcers (canker sores), are small, shallow lesions that develop in your mouth or at the base of your gums. Unlike cold sores, canker sores don't occur on the surface of your lips and aren't contagious. They can be painful, however, and can make eating and talking difficult. Possible causes: citrus fruits (e.g., oranges and lemons), physical trauma, stress, lack of sleep.