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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 at any time. It is especially likely to become active again during or after:

  • skin injury, such as a scrape or too much exposure to the sun
  • physical illness, such as a cold or flu
  • dental treatment
  • emotional stress
  • 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 after the first time, 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 healthcare 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 to confirm the diagnosis of herpes simplex virus. The test is called a viral culture.

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 healthcare provider may prescribe an oral antiviral medicine, such as acyclovir, valacyclovir, or famciclovir. This medicine stops the virus from making more viruses in your body. To prevent the blisters, the medicine must be taken when you first start having symptoms. The medicine does not get rid of the virus, but it can decrease the number of days you have symptoms and help the blisters dry up more quickly. If you have cold sores often, your provider may recommend taking antiviral medicine daily to try to stop outbreaks from recurring. Or your provider may prescribe an antiviral medicine for you to take when you know you are going to be exposed to something that causes you to have cold sores, such as a lot of sun or stress

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 often (for example, several times a year) or rarely, such as once every few years.

How can I take care of myself?

  • Taking a nonprescription painkiller such as aspirin, acetaminophen, or ibuprofen may help cold sores feel less painful. Check with your healthcare provider before you give any medicine that contains aspirin or salicylates to a child or teen. This includes medicines like baby aspirin, some cold medicines, and Pepto Bismol. Children and teens who take aspirin are at risk for a serious illness called Reye's syndrome. Ibuprofen is an NSAID. Nonsteroidal anti-inflammatory medicines (NSAIDs) may cause stomach bleeding and other problems. These risks increase with age. Read the label and take as directed. Unless recommended by your healthcare provider, do not take NSAIDs for more than 10 days for any reason.
  • Putting ice on the blisters may also help lessen the pain.

What can I do to help prevent cold sores?

Use a lip balm containing sunscreen whenever your lips are exposed to the sun. Avoid being out in the sun too much. This often causes outbreaks of blisters.


To prevent spreading the virus to other parts of your body:

  • 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, especially after putting medicine on the sores.
  • Take care to avoid spreading the virus to other susceptible areas of your body, such as the eyes and genitals.

To prevent spreading the virus to others:

  • Avoid kissing and any other contact of the sores with another person's skin.
  • Avoid sharing soaps, washcloths, cosmetics (especially lip balm, lipstick, etc.), and utensils for eating or drinking. Dispose of or wash your personal items (such as tissues and eating utensils) yourself.
  • 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).

To prevent getting the cold sore virus from someone else:

  • If you are caring for someone with the herpes virus, do not touch the sores directly. Use gloves or gauze to apply medicine.
  • Avoid kissing or touching another person's cold sore with any part of your body.
  • Avoid sharing soap, towels, cosmetics, food, or drink with someone who has cold sores.

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 oral4505.htm Release 13/2010

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