The Annoying, Painful, and Mysterious Canker Sore That familiar, throbbing sensation on the inside of your lip or cheek. A tiny white or yellow dot with a fiery red halo. You know what it is before you even look in the mirror: a canker sore. These little ulcers, also known as aphthous ulcers, are a common and unwelcome visitor for millions of us. While they’re generally harmless and clear up on their own, they can be incredibly painful, making eating, drinking, and even talking a challenge. But what exactly are they, and why do they keep popping up? What is a Canker Sore? A canker sore is a small, shallow ulcer that develops on the soft tissues inside your mouth. Unlike cold sores, which are caused by the herpes virus and appear outside the mouth on the lips, canker sores are not contagious. They can appear on your: They typically start as a small, tingling or burning sensation, and then a round or oval lesion forms, often with a white or yellowish center and a bright … [Read more...]