Many differences. Canker sores and cold sores are common disorders of the mouth, irritating millions of americans. Although many people use the terms canker sore and cold sore synonymously, they are different conditions. Cold sores are caused by the herpes virus and are contagious while canker sores cause is unclear and is not considered contagious.
Cold sore is herpes. Cold sores are on the lips or on the face near the lips. They are caused by recurrences of herpes virus, which lives in the nerves after an initial infection, and then travel down the nerves to cause the cold sores at the skin surface from time to time. Canker sores are inside the mouth, and are not from herpes, but are due to the immune system reacting to something on the inside of the mouth.