What are cold sores and blisters?

Cold sores and fever blisters are annoying, small, painful blisters on the lips and nearby skin, including in the nose and mouth. They usually appear during physical illness or emotional stress.

How do they occur?

The blisters are caused by a virus called herpes simplex virus type I. (The virus is related to herpes simplex virus II, which 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 blisters.

Once you are infected, the virus continues to live in the nerve cells of the skin, even after the blisters are gone. Injury, such as a scrape or too much exposure to the sun, and physical illness, such as a cold, seem to cause the virus to become active again. When it is active, the virus causes more fever blisters or cold sores. The blisters also may appear during emotional stress.

Once you are infected with the virus, it is not possible to predict how often you will have the blisters. 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 a yellow crust forms on the tops of the blisters and they become less painful.

How are they diagnosed?

Your health care provider can determine from your history and a physical exam whether the blisters are fever blisters. Lab tests of fluid from the blisters (called viral cultures) may be performed.

How are they treated?

There are many over-the-counter (nonprescription) medications that can be used to treat the symptoms of fever blisters. However, they may not be as effective as you'd like.

Your health care provider may prescribe acyclovir. This medication can decrease the number of days you have symptoms and speed the drying up of the blisters. It may also help you to have the blisters less often. It has the disadvantage of being expensive.

How long will the symptoms 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.

How can I take care of myself?

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

What can I do to help prevent fever blisters?

Avoid direct contact with the blisters and with items that touch the sores, such as eating utensils and facial tissues.

You and others around you should practice good handwashing.

Take care to avoid spreading the virus to other susceptible areas of your body, such as the eyes and the genitals.

Just as genital herpes can be spread to the mouth by oral- genital sex, fever blisters can be spread to the genitals by oral-genital sex. Be careful not to pass the oral fever blisters to your sexual partners.

Use a lip balm containing sunscreen whenever your lips are exposed to the sun.