A small blister that appears on or around the lip area, and often filled with some kind of liquid is called as cold sores. These sores are very sensitive to the rapid changes occurring in the environment and are extremely painful for the person, and are therefore referred to as cold sores. These sores are created by a virus that spreads easily from person to person and is called as the herpes virus. Cold sores are a very common problem for the mouth a lot of people around the world. The type 1 virus cold sores are contagious in spreading spreads, while type 2 viruses spread as genital disease.