Causes and Diagnoses

Causes and Diagnoses of Cold Sores

Infection with the herpes simplex-1 virus causes cold sore outbreaks. You can catch HSV-1 from someone else who has the virus—active or not—by kissing and sharing beverages, eating utensils, napkins and towels. It can also be spread by sexual contact with someone who has genital herpes.

Repeated outbreaks may occur when you are stressed, sick, overtired or have been out in the sun too long.

Diagnosing cold sores

Your physician can usually diagnose a cold sore during a physical exam. Rarely, a biopsy (tissue sample) from the blister can be taken to confirm the type of virus in a lab.