Medically known as recurrent herpes labialis, cold sores, or “fever blisters,” are groups of painful, fluid-filled blisters that tend to cluster on or around the lips, though they can occasionally affect the tongue, gums and the hard and soft palate. Herpes Simplex Virus Type 1 (HSV-1) is the most common virus that causes cold sores and is usually acquired through direct contact with infected lesions or body fluids such as saliva.

In the United States, 31.1% of children ages 6 to 13 have tested positive for HSV-1 antibodies, according to data from the 1999-2002 National Health and Nutrition Examination Study. More than 25 percent of children were infected by age 7 and most people will be infected by adulthood. However, recurring cold sores appear only in 14 to 40 percent of infected individuals, according to a 2002 report by the National Institute of Dental and Craniofacial Research.

Symptoms & Causes

Only few people infected with HSV-1 will develop a primary infection with symptoms right after they are first infected,  and only a portion of those people will go on to experience recurring cold sores, according to a 2002 article in the Journal of the American Dental Association. Recurrent cold sores occur when the virus held dormant in the nerve tissue is reactivated. Common triggers of cold sores include ultraviolet light, oral trauma, fatigue, stress and menstruation, according to the National Institutes of Health.

Diagnosis & Tests

Patients with recurrent cold sores usually experience tingling, itching and burning sensations before blisters and lesions appear, according to data from a 2007 review from the Harvard School of Dental Medicine. Lab tests such as viral isolation in tissue culture and direct immunofluorescent antibody testing are available to confirm the diagnosis, though they are rarely used on otherwise healthy patients.

Cold sores are different from canker sores, which are small ulcers that usually appear inside the mouth and are not caused by the HSV-1 virus.

Treatment & Medication

In an otherwise healthy person, cold sores will heal spontaneously without scarring in seven to 10 days. Most treatments for cold sores target the symptoms, not the virus, and are most effective when they're applied at the first sign of symptoms. Over-the-counter protectants and anti-inflammatory creams can be applied over the blisters to provide temporary relief, but they have only minor effects on how fast they heal, according to a 2008 article published in the journal Canadian Family Physician. However, lysine supplements could possibly reduce the number and duration of outbreaks, according to the University of Maryland Medical Center.

Oral antiviral medication, such as acyclovir (under the brand name Zovirax) or famciclovir (Famvir), are usually prescribed to immunosuppressed patients. Although these can be ineffective after three to four days of blisters, some studies, including a double-blind study by the University of Utah, have shown that antiviral medication can help the sores heal faster and make the sores less painful.


Since herpes virus is contagious, it's best to avoid direct contact with cold sores and avoid sharing personal items such as razors and towels. Current research on the whether antiviral creams and sunscreen can prevent cold sores is contradictory based on several trials, according to the Canadian Family Physician article. However, if the virus returns frequently, oral antiviral medication may reduce the frequency of cold sores.