What is a cold sore?

"fever blister": Cold sores are little blisters that form on the lips or mouth. They are caused by a herpes simplex virus. The blisters often break open and leak a clear fluid, then scab over after a few days.

Viral infection: A "cold sore" is caused by an infection by herpes virus type i. Most of us are infected by this type of virus in childhood. We get better, but the virus becomes dormant in our bodies and can be reactivated, causing cold sores. The virus is often reactivated by illness or stress.

A virus infection: Cold sores on the lips or near the lips, are usually caused by oral herpes virus. They start as a slightly raised reddish area, then form a cluster of tiny blisters, which break open the next day, leaving a sore (ulcer) to heal up over a week. Sores appear more often when a child is under stress or is ill from another illness. Younger babies with herpes should see a doctor when a sore appears.