Dec 22, - Cold sores are often known as fever blisters given their appearance. Most cold sores are caused by HSV-1, also known as Herpes Simplex Virus. While a majority of HSV-1 cases involve oral herpes or cold sores, around 40 percent of cases involve genital sores. Herpes can be described as a very common condition that affects both men and women. There are two different types of viruses that can cause herpes, though.