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Medical Author:

Mohamad El Mortada, MD

Medical Author:

MaryAnn Tran, MD

Medical Author:

Corrine Young, PharmD

Medical Author:

Mary Nettleman, MD, MS, MACP

Mary Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.

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Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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The diagnosis of cold sores is usually based on the appearance of the lesions. Usually, no laboratory test is needed because most sores that look like cold sores are cold sores. Occasionally, mouth sores known as canker sores may be mistaken for cold sores. However, canker sores occur inside the mouth whereas recurrent cold sores usually occur on the lips. If there is a question about the diagnosis, a variety of tests are available, including viral culture and polymerase chain reaction (PCR). To do these tests, a swab is rubbed over an active blister. Swabbing the blister in an attempt to culture the virus in the lab works best in the first 24-48 hours before the blister has crusted over. There is also a way to test for herpes DNA in a swab that has been rubbed on the sore. This type of testing is called a "polymerase chain reaction" or PCR for short. PCR testing is very good at detecting herpes virus, but it is not as readily available as culture.

Blood tests for antibodies are not very useful, because finding antibodies to herpes just means that the body has been exposed to this virus at some point in the past. It does not tell if the current sore is due to herpes.

If the diagnosis is in doubt, the best approach is to encourage the person to see a doctor at the first sign of a sore. That will allow the clinician to see active lesions that can be tested by culture or PCR. If a delay is anticipated in being seen, a mobile phone or camera can be used to take pictures of the lesion to show to the physician.

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