|Cold sores form as a cluster of small blisters on the lips, around the corners of the mouth, or sometimes inside the nose. They are also referred to as fever blisters, and the medical term for them is recurrent herpes labialis.
Once the cold sores develop, the blisters are more obvious and clearly recognizable. When the blisters break, an extremely painful, moist sore develops. Thereafter, a crust or scab forms over the sore.
Cold sores are caused by a highly contagious viral infection, the herpes simplex virus-1 (HSV-1). If you are exposed and infected with the herpes virus, it may stay dormant in your system forever, with occasional bouts of activity and infection.