Approximately one in three people has one sometimes: a cold sore. Painful, annoying blisters that keep coming back. A cold sore is caused by the herpes virus. And if you ever become infected by this virus, it will stay in your body for the rest of your life. So, you will never truly get rid of that cold sore. In this video virologist Michiel van Gent (ErasmusMC) tells you something about the clever hiding tactics of the herpes virus and how it keeps on avoiding your immune system.