Cold Sores Caused by Herpes Virus

The Eyesores of Cold Sores

Herpes Cold Sore on Mouth
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For most healthy individuals, the recurrence of cold sores is more of a nuisance than a serious health issue. In contrast to canker sores, which are noninfectious sores that occur on the inside of the mouth, these unsightly red blisters form on the outside of the mouth and are caused by a common and contagious virus.

Microbe Name

Herpes simplex virus type 1 (HSV-1); most cold sores are caused by HSV-1, whereas sexually transmitted herpes infections are mostly caused by HSV-2.

However, there is some overlap between the sites of infection and the herpes type.

Type of Microbe: DNA virus

How It Spreads

Cold sores are spread from person-to-person, usually between family members or other close contacts. They are most contagious when the sore is open and releasing fluid. The cold sore virus is spread through kissing or sharing items that have touched the mouth or lips of an infected person. It can also be spread through sharing of towels or utensils. And, it can be spread even when there are no symptoms (obvious cold sores).

How It Causes Disease

Once a person is infected, the virus can hide out in the nerve cells. Stress to the body can cause the virus to come out of the nerve cells and cause cold sores. Sources of stress include a cold or other infection, long exposure to sunlight, menstrual periods, emotional stress, digestive problems, and lip injuries.

Who’s at Risk? All people are at risk, but many infections occur during early childhood.

Approximately 8 out of 10 people have the virus.


Cold sores are fluid-filled blisters that appear on the lips and near the mouth. Initial infection with the virus varies from person to person. It can have no symptoms, or it can begin with a severe viral syndrome consisting of fever, body aches, and a sore mouth or throat.

The initial infection is most likely to also cause gingivostomatitis, or ulcers in the mouth, lips and throat of young people. Herpes labialis (cold sores) is usually a sign that the virus has been re-activated. Once a person gets infected, he or she will be infected for life. Recurrent outbreaks of cold sores occur in the absence of other symptoms.

Early symptoms of cold sore development include a tingling sensation where the sore will appear. Within 1 to 2 days, a fluid-filled blister appears, and clusters of larger blisters may appear. By day 4, the blisters break open, and the reddish sore turns gray. By day 5, scabs begin to form. They may undergo a few cycles of breaking and re-scabbing, until the cold sore disappears.

Diagnosis: Cold sores can often be diagnosed by their location and appearance. However, a viral culture is the best way to test for HSV-1. Additionally, there are other tests that may be used.

Prognosis: Most cold sores resolve within 7 to 12 days.


Antiviral medications are available for treatment of primary infection with HSV-1. Treatment for cold sores after you've already been infected might be recommended if you are someone with a "prodrome" (you can feel the lesion coming on).

Lysine (an amino acid supplement), is also available to help prevent the development of cold sores -- most useful in people who have frequent or severe recurrences. Gels containing lidocaine can help with pain. See your health care provider for recommendations and prescriptions of cold sore treatments.


To prevent getting the virus, avoid kissing people who have blisters on their mouths, wash your hands frequently, and do not share personal items, especially with people who have cold sores. To prevent cold sore outbreaks, maintain a healthy lifestyle, reduce sun exposure, and use lip balm on dry or injured lips.


A herpes viral infection can be fatal for people who have weak immune systems, including people with HIV or undergoing chemotherapy. For these people, the lesions can become huge, painful and disfiguring. HSV-1 can also spread to other parts of the body, including the fingers (herpetic whitlow), eyes (conjunctivitis, keratitis), and genital area (genital herpes). Some serious but rare complications can arise from eye infections, leading to blindness, infection of skin in children with eczema (eczema herpeticum) and infections in the brain (herpes encephalitis and meningitis).


Cold Sores, MedlinePlus. National Library of Medicine. National Institutes of Health.