Cold sores normally appear on the outside of the mouth, around the lips. Sores inside the mouth may occur, but are more common in children under the age of five. When cold sores do appear inside the mouth it is usually in non-movable areas, such as the gums or roof of the mouth.  Sores inside the mouth may be canker sores, also known as aphthous ulcers. Like cold sores, canker sores can be a recurring problem and quite painful. Unlike cold sores, however, canker sores are not contagious.