Cold Sores / Fever Blisters Fever blister, also known as cold sores are a nuisance that causes annoyance and discomfort to millions of Americans. The condition is caused by a contagious herpes virus, either herpes simplex one or herpes simplex 2. Over 95% of cases are caused by herpes simplex virus one (HSV1). The virus causes “blisters” or small sores that are found on the face, lips, or in the mouth or in the nostrils. These sores cause pain, itching, and burning … [Read more...] about What Causes Fever Blisters?