It is the morning of your big presentation and you have an ugly cold sore on your upper lip. Why do cold sores always seem to appear when you have something important to do? Is it just bad luck?
What causes the cold sore is a virus called herpes simplex type 1 or type 2. Almost everyone in the whole world carries this virus. Stress is the main trigger for causing the virus to become active and appear as cold sores to break out.