What Is a Cold Sore?
Cold sores are also sometimes called fever blisters. They are contagious lesions filled with fluid that most often form around the mouth, but may also appear in your nostrils, on your chin, or on your fingers.
A cold sore is caused by herpes simplex virus type 1. It usually begins with a prodrome, a pain or tingling sensation. The prodrome typically occurs one to two days before the cold sore appears. The lesion will eventually dry up, but cold sores can last from 10 to 14 days and can be recurring.
Once you have been infected with the herpes simplex virus type 1 and an outbreak occurs, the virus can then go dormant for extended periods of time. Later it can return as an active infection near the original outbreak site. Breakouts most often occur when you are overly tired or stressed, but fever, menstruation, and sun exposure can also cause the active infection to resurface.
Although both are lesions that occur near the mouth, cold sores are different from canker sores. Cold sores are viral and occur around the mouth; canker sores develop on the soft tissue inside the mouth and are considered ulcers. Canker sores are not caused by the herpes simplex virus.