Cold sores  are a common viral infection, which are also sometimes called fever blisters. They are tiny blisters around and on your lips that are fluid-filled. These blisters are usually grouped together to form patches. A scab forms after the blisters that break, and this scab can last many days. Without leaving a visible scar, cold sores typically heal in about two to three weeks.
A fever, or sore on the lips, is usually caused by herpes simplex virus type I. More than 90%  of people worldwide are infected with it.
This means that the virus constantly lives in the body, but mostly “sleeps”; not everyone has manifestations of the disease.
What Is Herpes?
Herpes  is a virus that infects a cell by invading its genetic apparatus. It is completely impossible to get rid of the virus. However, he usually does not manifest himself in any way.
The most common symptoms of herpes are blistering rashes that can appear on the lips, mucous membranes of the nose and mouth, on the genitals and on the body