Cold sores and canker sores are both types of oral lesions, but they have distinct differences. Cold sores, also known as fever blisters, are small, fluid-filled blisters that appear on or around the lips, nose, or chin. They are caused by the herpes simplex virus and are contagious. Canker sores, on the other hand, are small, shallow ulcers that appear inside the mouth, usually on the tongue, inner cheeks, or gums. They are not contagious and the cause of them is not entirely understood, but they are thought to be due to a combination of factors such as genetics, stress, and certain foods.