What causes cold sores and fever blisters?

Cold sores and fever blisters are caused primarily by the herpes simplex virus type 1 (HSV-1). Herpes simplex virus type 2 (HSV-2), which usually causes genital herpes infections, is also now known to infect the face and mouth and cause cold sores. HSV-1 and HSV-2 are very common viruses among humans and are easily spread from person to person.

Infection occurs when someone is exposed to the virus by contact with fluids containing herpes virus from an infected person. Simple things like kissing, sharing of utensils and drinks, and not washing hands after touching blisters can result in the spread of HSV to others and cause infection. Furthermore, it is suspected that oral-genital sexual contact with an infected person can also lead to HSV-1 or HSV-2 cold sores.

Once infected, the virus continues to live in nerve cells within the skin. The virus lays dormant in nerve roots until the time it might resurface and cause a cold sore outbreak. Recurrent cold sore outbreaks can be triggered by emotional or physical stress. Trauma, illness, menstruation, and sun exposure can all activate dormant herpes virus. It is not possible to predict the frequency or severity of recurrences; in fact some people may never have a recurrence at all.

What are the symptoms?

There are two types of HSV infections: primary and recurrent. Primary infection after initial exposure is often associated with fever, headache, sore throat, and malaise, as well as the characteristic blisters. Sores of a primary infection appear two to twenty days after contact with an infected person and can last from seven to ten days.

Recurrent cold sores usually affect the same location as the initial outbreak. They are usually less severe than primary infections and associated symptoms are often absent. Sores tend to be smaller, less painful, and of shorter duration, resolving in an average of 5 days.

Both primary and recurrent cold sore outbreaks are often preceded by a sense of numbness, itching, tingling, or burning around the area where blisters will form. These “prodromal symptoms” may occur 1 to 48 hours prior to the appearance of blisters.

As the blisters emerge they fill with virus containing fluid and can be painful. Over the next two to three days the sores may ooze and then form a yellow crust. Eventually, the crusts fall off, leaving slightly red skin, which usually heals completely and rarely leaves a scar.

How can you avoid cold sores?

Avoiding infection by HSV is the only sure way to avoid getting cold sores; unfortunately, this is no easy task.  This requires careful avoidance of contact with virus containing fluids from infected people. Kissing, sharing of foods, beverages, utensils, towels, toothbrushes, etc. with someone with active cold sores is a sure way to get infected. This also requires individuals infected with HSV-1 or HSV-2 to actively avoid exposing others to the virus. Sexual partners should be informed of herpes status prior to engaging in behaviors with high risk of transmitting HSV.

Avoiding triggers, such as physical or emotional stress, can minimize recurrent cold sore outbreaks.

How can you treat active cold sores?

Herpes labialis is often left untreated and outbreaks usually resolve on their own without scarring. Good wound care is essential to avoid secondary bacterial infection of the involved tissue. The sores should be kept clean and picking at sores or crusts should be avoided in order to promote quick healing and limit spreading of the virus containing blister fluids. Prescription and nonprescription medications may be used to effectively control symptoms and expedite healing.

Your physician may prescribe certain oral or topical antiviral medications in order to treat HSV infections. Topical antiviral medications such as 5% acyclovir ointment (Zovirax) and 1% penciclovir cream (Denavir) are frequently used for recurrent herpes labialis cold sores. Both products may shorten the duration of pain and time to healing of the sores. They must be applied soon after the first sign of a recurrence and every two or three hours while awake for 4 or more days. Antiviral drugs like acyclovir (Zovirax), famciclovir (Famvir), and valcyclovir (Valtrex) may also be taken orally to shorten the duration and severity of primary infections and severe recurrences.

Over-the-counter products are also effective in treating cold sore outbreaks. Analgesics such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) can help control, fever, aches, and pain associated with primary infection or recurrent outbreaks.

Topical anesthetics, such as tetracaine, benzocaine, lidocaine, or camphor are effective for quick relief of pain and itching. Tetracaine cream has also been shown to reduce time to healing of cold sores in clinical trials compared with placebo.  These agents are available as creams, ointments, gels, and lotions under a variety of brand names, such as Hurricaine, Campho-Phenique, Orabase, Orajel, Zilactin, and others.  All usually require frequent application and are suitable for use around the mouth.

Newly available is 10 % docosanol cream (Abreva) approved by the FDA for the over-the-counter treatment of herpes labialis. Docosanol appears to inhibit viral entry into cells, which is required for viral replication and infection, a mechanism different from prescription antiviral medications. In clinical studies docosanol showed a similar reduction in the average time to healing of sores as prescription penciclovir cream. Like the prescription topical antiviral medications, Abreva must be started early after the first sign of recurrence and applied five times daily.

Where can you get more information and help?

Providers at the Campus Health Service are available for accurate diagnosis, treatment, and monitoring of cold sores and other herpes infections.  They can also provide more information on the best care for your cold sores and fever blisters.

The Campus Health Pharmacy is also available to supply all your prescription and nonprescription products for cold sore care. Along with the prescription antiviral medications, the pharmacy has available over-the-counter analgesics (acetaminophen and ibuprofen), topical anesthetics (Hurricaine, Blistex, and Carmex), and the latest in the fight against cold sores, Abreva.  And, as always, the pharmacy is staffed with friendly, educated professionals who provide information regarding the safe and effective use of all available products.