What causes cold sores? Cold sores are a symptom of infection by the Herpes Simplex Type 1 virus in the human nervous system. This is not as bad as it sounds (gee, that’s reassuring, huh? lol)–no, really, oral herpes is harmless, annoying, but harmless. However, regrettably, the virus will stay in your nervous system forever (although I do cover a ‘cure’ at the end that will ensure you don’t ever get another outbreak)….