Picture of Cold Sore and Canker Sore

Cold sores and canker sores aren't the same. Cold sores usually appear on the lip; canker sores affect the inside of the mouth. Canker sores don't involve the herpes virus and aren't contagious. Their cause is unknown. Cold sores generally herald their arrival with a warning period of red, irritated skin. Blisters form, rupture, then crust over before healing.