ANDY'S ANSWER:  Cold sores are caused by the herpes simplex virus. The herpes simplex virus is very common because it is so easily spread. Some people have been infected by their own parents at a young age, by being kissed by them or by sharing eating utensils, cups, etc. with them. Once you have the virus, there is no way to get rid of it from your body - it stays with you for life. The only thing you can do is try to minimize your outbreaks (which can be very painful) and try not to infect other people.