The virus that causes
cold sores is common. Most people have been infected
with this virus (herpes simplex virus, or HSV) by the
time they reach adulthood.
Although most people have been exposed to HSV, only about 20% to 40%
develop recurring cold sores.1 After a person becomes
infected, the virus remains inactive in the body until it is triggered by
something such as sunlight exposure or stress. When active, the virus results
in a cold sore outbreak.