What is the cause of cold sores?

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

Direct Contact: Cold sores are caused by the herpes simplex virus (hsv). They are typically transmitted through broken skin. Sometimes through kissing, sharing eating utensils or drinking cups, or other forms of touching another person's saliva.