What Is It?
Cold sores and fever blisters are caused by localized viral infections, which typically cause clusters of blisters on the lip and, rarely, inside the mouth. They are caused by the herpes simplex virus type 1 (HSV-1), a virus that passes from person to person by direct contact with infected skin or saliva. Once HSV-1 invades the skin, it causes a primary infection, which usually occurs in childhood, causing a fever, sore mouth and sore throat. After this primary infection subsides, the virus remains dormant indefinitely in nerve roots near the affected skin area. In some patients, the virus intermittently reactivates to cause herpes recurrences (secondary herpes episodes), which produce cold sores and fever blisters. Recurrences can be triggered by many factors, including fever, stress and trauma to the lips or exposure to the sun's ultraviolet rays.
In addition to causing infections around the mouth, HSV-1 can be transferred to the eyes, the skin of the fingers, the genital area and elsewhere. Although most genital herpes infections are attributed to herpes simplex type 2 (HSV-2), HSV-1 can be an alternate cause in some patients. HSV-1 can cause unusually severe illness in debilitated people, especially those suffering from malnutrition, cancer or weakened immune systems, including people with AIDS.
HSV-1 infections are very common in the United States, and most of us are infected by the time we reach adulthood. Even if we do not remember having a primary HSV-1 infection during childhood, the fact that we occasionally have a cold sore or fever blister indicates that HSV-1 is present.
A primary herpes infection — the first time a person is infected — may not cause any symptoms. However, in many patients, it causes fever, painful swelling and open sores on the gums and inside the cheeks, a painful pharyngitis (throat infection) that is mistaken for "strep throat," or another form of bacterial pharyngitis. These symptoms usually begin approximately a week after exposure to someone with HSV-1.
Cold sores and fever blisters are symptoms of a herpes recurrence; they may occur spontaneously or after a period of illness or stress, poor nutrition, a dental extraction or sunlight exposure. Dental procedures that stretch the lip may also occasionally cause recurrent herpes. The border of the lip is by far the most common place for recurrences to appear. They may occasionally erupt inside the mouth, particularly in patients with compromised immune systems or those debilitated by other medical disorders. Most ulcers inside the mouth are not caused by herpes.
The first sign of a recurrence is a vague tingling and itching in the affected area, followed by swelling and redness. Within 24 to 48 hours, one or more tiny blisters ("fever blisters") appear. These blisters break, leak fluid and form painful sores ("cold sores"), which are eventually covered by crusts and scabs.
Your dentist or physician usually can diagnose cold sores and fever blisters by simply examining the affected area of skin. More sophisticated methods of diagnosis include virus cultures, immunofluorescence (IF) or immunoperoxidase (IP) studies to detect HSV-1 in cells scraped from the infected area. An enzyme-linked immunosorbent assay (ELISA) can detect HSV-1 in infected cells. The sophisticated tests usually are not necessary in otherwise healthy patients.
Symptoms of a primary HSV-1 infection may last for one to two weeks. After this infection subsides, HSV-1 remains dormant in a patient's nerve cells for the rest of his or her life. During herpes recurrences, cold sores and fever blisters usually crust within four days and heal completely within 8 to 10 days.
You can help to prevent a primary herpes infection in children by not allowing them to be kissed by anyone who has cold sores, fever blisters or signs of a primary herpes infection. However, despite these protective measures, most children will be infected with HSV-1 by the time they reach adulthood. Currently, several different vaccines are being developed against HSV-1, but these will only protect people who have never been infected. They will not prevent eruptions of cold sores and fever blisters in people who already have HSV-1.
There is some preliminary evidence that using sunscreen on the lips will prevent sun-induced eruption of cold sores and fever blisters. For patients with a weakened immune system, antiviral medications may be used to suppress HSV-1 recurrences.
Cold sores and fever blisters can be treated with antiviral medications. These medications are of little value if therapy is started after the blisters appear. Topical antiviral creams shorten the healing time of fever blisters by less than one day. Antiviral drugs taken by mouth are useful for preventing cold sores at high altitudes or in tropical locations where exposure to the sun can trigger an outbreak. Wind and other weather conditions also can trigger cold sores if your lips become overly dry. It also helps to keep the area clean and to apply soothing lip balm if the lips are involved. Try not to touch the affected area and avoid kissing anyone while blisters and sores are present.
When To Call A Professional
Speak with your dentist or physician about the best way to deal with cold sores and fever blisters. These skin problems affect almost everyone occasionally and generally are of no danger. However, cold sores can be severe and life-threatening in people who are immunosuppressed. Call your dentist or physician immediately if lip or mouth sores persist, make it hard for you to talk or swallow, or if you develop a fever or severe headache.
The HSV-1 infection that causes cold sores and fever blisters is a lifelong problem. It can be minimized by limiting sun exposure and wearing sun block.
American Social Health Association
P.O. Box 13827
100 Capitol Drive
Research Triangle Park, NC 27709-3827
Phone: (404) 639-3311
Herpes Hotline: (919) 361-8488
To Order Materials: (800) 230-6039
Centers for Disease Control and Prevention (CDC)
1600 Clifton Rd., N.E.
Atlanta, GA 30333
Toll-free: (800) 311-3435
Phone: (404) 639-3534
STD Hotline: (800) 227-8922