I have red blister in my lower lips and it burns. what could be this problem?

Use Viroxyn: Although cold sores and canker sores are often confused for each other, they are not the same. Cold sores, also called a fever blister or herpes simplex type 1, are groups of painful, fluid-filled blisters. Unlike canker sores, cold sores are caused by a virus and are extremely contagious. Also, cold sores typically appear outside the mouth -- usually under the nose, around the lips, or under the.