Cold sores are small blisters around the mouth, caused by the herpes simplex virus.
The most common strain of the virus is herpes simplex virus 1. Herpes simplex is not curable, but may lay dormant for long periods of time. Episodes of the cold sores last no longer than two weeks. Hot sun, cold wind, a cold, or a depressed immune system can cause an outbreak of herpes simplex virus. The following are the most common symptoms of cold sores.