How are cold sores diagnosed?

Suspected cold sores should be diagnosed by a clinician in order to differentiate between herpes simplex virus (HSV) and other causes of oral sores. Cold sores are often diagnosed by visual inspection, but lab tests can also be performed, including viral culture and/or polymerase chain reaction (PCR) testing of a fresh swab taken from the active sore. Blood tests for HSV antibodies can be done but aren’t as useful for diagnosis, because being HSV-positive doesn’t mean a person will get cold sores. Many people with HSV antibodies will never get cold sores.^[1][2]