My 13 year old daughter is suffering with swollen lips and a blister, that looks like a cold sore. However, she has a very dark line of dry scaly skin around both the top and bottom lips. This area sometimes itches and burns. Earlier this year she had an episode that started with a sore throat, but ended with blisters that covered her entire lips. The lips were also swollen and the same dark line around the mouth was present. What could be causing this?