What causes of cold sore?

Learn about HSV: Cold sore = herpes....It has nothing to do with 'having a cold'. It's a common infection and can be transmitted whenever a sore is present and even when one is not.

Cause is herpes: simplex virus. Triggers for cold sores can include illness, stress, fatigue, becoming physically cold, dry air, UV rays (sun), mouth trauma or one's period.

Cold sore: Cold sore is caused by virus called Herpes simplex . Most common way to catch it through kiss. It can present as tingling followed by blister formation which can last for few days. It is very infectious . usually blister leads to scab which disappears over few weeks but virus can lay dormant in nerve and can get activated at later stage . http://patient.info/health/cold-sores-leaflet

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 person is under stress or is ill from another illness. (Babies with herpes should see a doctor if a cold sore appears.)