Cold Sores (Fever Blisters)

What are cold sores?

Cold sores are annoying, small, painful blisters on the lips and nearby skin, including in the nose and mouth. They usually appear when you are sick or stressed. They are also called fever blisters.

How do they occur?

Cold sores are caused by the herpes simplex virus. This virus also causes genital herpes. The fluid in the blisters contains live virus. The virus in this fluid can easily be spread from one person to another. The infection can be spread, for example, by kissing, by sharing food or drink, or by not washing your hands after touching the sores.

Once you are infected, the virus continues to live in the body, even after the sores are gone. The virus may become active again and cause more cold sores during or after:

injury, such as a scrape or too much exposure to the sun
physical illness, such as a cold
dental treatment
emotional stress or fatigue
hormonal changes caused by pregnancy or a woman's menstrual cycle.

It is not possible to predict how often you will have cold sores. Some people never have them again, but others have them regularly.

What are the symptoms?

About 24 hours before you can see blisters, you may have a sense of numbness, tingling, itching, or burning. Then a small cluster of tiny blisters appears on your lip or the skin around your lips. The blisters may be somewhat painful. Over the next few days, the blisters break and fluid drains out. This fluid is very contagious. As the blisters dry, they become sores that are covered with a yellowish dried crust and they become less painful.

How are they diagnosed?

Your health care provider can usually determine from your history and a physical exam whether the blisters are fever blisters. Fluid from the blisters may be tested in the lab (viral cultures).

How are they treated?

There are many nonprescription medications that provide some relief from the symptoms. A nonprescription antiviral medicine applied several times a day to the area as soon as the symptoms start may lessen symptoms. It may also help the sores heal more quickly.

Your health care provider may prescribe an oral antiviral medicine, such as acyclovir, valacyclovir, or famciclovir. This medicine stops the virus from reproducing itself. It must be taken when you first start having symptoms. The medicine does not eliminate the virus from the body, but it can decrease the number of days you have symptoms and speed the drying up of the blisters. Your provider may recommend taking antiviral medicine daily to stop outbreaks from recurring.

How long will the effects last?

The blisters usually last 7 to 10 days. They should be considered contagious as long as you have any moist secretions from the blisters. They may return several times a year or a few years later.

How can I take care of myself?

Taking a nonprescription painkiller such as aspirin, acetaminophen, or ibuprofen may help cold sores feel less painful.
Putting ice on the blisters may also help lessen the pain.

What can I do to help prevent fever blisters?

Avoid touching any area of the body where there is tingling, itching, burning, or blisters. (This is very important when the blisters are draining.) Also avoid contact with items that touch the sores, such as eating utensils and facial tissues.
Practice good hand washing.
Take care to avoid spreading the virus to other susceptible areas of your body, such as the eyes and the genitals.
Avoid kissing and other contact with the mouth.
Avoid sharing soaps, washcloths, cosmetics (including lip balm), and eating or drinking utensils.
Just as genital herpes can be spread to the mouth by oral-genital sex, cold sores can be spread to the genitals by oral-genital sex. Be careful not to pass the oral cold sores to your sexual partner(s).
Use a lip balm containing sunscreen whenever your lips are exposed to the sun.
If you are caring for someone with the herpes virus, do not touch the sores directly. Use gloves or gauze to apply medicine.

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.

HIA File INF4505F.HTM Release 9.0/2006