A canker sore is typically one that occurs on the delicate tissues inside your mouth. It is usually light-colored at its base and can have a red exterior border.
A cold sore or fever blister, on the other hand, usually occurs on the outside of the mouth, usually on or near the nose or lips. A cold sore is contagious because it is caused by the herpes simplex virus, and it is usually painful and filled with fluid.
In most cases, patience is the best medicine for treating canker sores. A healthy diet and good oral hygiene are usually the best remedy, but some special rinses and anesthetics can help. Cold sores can be treated effectively with some over-the-counter topical creams; sometimes, an antiviral medication will be prescribed by your doctor.