Cold sores and fever blisters are generated by herpes simplex virus type 1 (HSV-1), which is passed on from person to person through saliva (either directly, or by using the same glass or cup) or from skin contact. Cold sores usually show up as clusters of small blisters on the lip. Most people first get infected with HSV-1 before they become ten years old.
After the first infection, the virus will stay dormant in the nerves of the face. In some people, the virus get’s active from time to time. When this happens, the cold sores appear. HSV-1 can get active from a cold or fever.
Stress is also able to create a cold sore outbreak. Mental and emotional stress, along with dental treatment, illness, trauma to the lips or sun exposure can create the outbreak. HSV-1 is also able to infect the eyes, the skin at the fingers, and the genitals. Most genital herpes infections come from herpes simplex type 2 (HSV-2).
HSV-1 is able to create serious illness in those with other health problems. The virus is able to cause serious illness to people who has an immune systems that has been weakened by either illness or medicines.