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.
Reviewed by Laura J. Martin, MD on August 03, 2010
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Text: "Dental Health and Canker Sores", WebMD Medical Reference