Cold Sore (Fever Blister)

What is a cold sore?

A cold sore is a small, painful blister on or around your lips or inside your nose or mouth. Cold sores usually appear when you are sick or stressed. They are also called fever blisters.

What is the cause?

Cold sores are caused by the herpes simplex virus. Fluid in the blisters contains live virus. The virus can easily spread from one person to another by:

  • Kissing
  • Sharing food, drink, or eating utensils
  • Not washing your hands after touching the sores

Once you are infected, the virus keeps living in your body even after the sores are gone. The virus may cause more cold sores at any time. This is more likely during or after:

  • Skin injury, such as a scrape or burn
  • Too much exposure to the sun
  • Physical illness, such as a cold or flu
  • Dental treatment
  • Emotional stress
  • Tiredness
  • Hormone changes caused by pregnancy or a woman’s menstrual cycle

What are the symptoms?

About 24 hours before you can see blisters, you may feel numbness, tingling, itching, or burning around your lips, nose, or mouth. Then a small cluster of tiny blisters appears on or around your lips or inside your nose or mouth. The blisters may be 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 are less painful.

How is it diagnosed?

Your healthcare provider will ask about your symptoms and medical history and examine you. Fluid from the blisters may be tested in the lab to check for virus.

How is it treated?

A nonprescription antiviral medicine called docosanol (Abreva) may lessen symptoms. It may also help the sores heal more quickly. Put the medicine on the area with blisters according to the directions on the medicine package. Many other nonprescription medicines can make the sores less painful, but they don’t help the sores heal.

Your healthcare provider may prescribe an oral antiviral medicine. The medicine does not get rid of the virus, but it can decrease the number of days you have symptoms and help blisters dry up more quickly. Taking the medicine when you first start having symptoms may help prevent blisters.

The blisters usually last 7 to 10 days. They should be considered contagious as long as you have any drainage 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?

To help relieve pain:

  • Take a nonprescription pain medicine.
  • Put ice on the blisters.

How can I help prevent cold sores?

If you have cold sores often, your provider may tell you to take antiviral medicine daily to try to help prevent cold sores. 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, like a lot of sun or stress. Take your medicine as directed by your healthcare provider.

Use a lip balm containing sunscreen whenever your lips are exposed to the sun. Avoid being out in the sun too much.

To keep from spreading the virus to other parts of your body:

  • Wash your hands well after you touch any part of your body where there is tingling, itching, burning, or blisters. It’s especially important to do this after you put medicine on the sores or when the blisters are draining.
  • Don’t touch your eyes or genitals after you touch the area around the cold sore.

To keep from spreading the virus to other people:

  • Avoid kissing or touching others with your mouth when you have a cold sore.
  • Avoid oral sex when you have a cold sore. The virus could spread to your partner’s genitals.
  • The virus can spread even when you don’t have symptoms. It’s more likely to cause infection in another person if they have a cut, rash, or sore that lets the virus enter their skin during, for example, kissing. Because the virus can spread when you don’t have symptoms, you may want to use latex or polyurethane condoms during foreplay and every time you have vaginal, oral, or anal sex. Because condoms don’t cover all areas of contact, the virus could still spread to your partner. This can be especially concerning if you are starting a new relationship. Discuss any questions you may have about this with your healthcare provider.
  • Avoid sharing soaps, washcloths, cosmetics (especially lip balm or lipstick), and utensils for eating or drinking.

To keep from getting the cold sore virus from someone else:

  • If you are caring for someone with the herpes virus, don’t 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.
Developed by RelayHealth.
Adult Advisor 2015.1 published by RelayHealth.
Last modified: 2014-04-07
Last reviewed: 2014-02-07
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright ©1986-2015 McKesson Corporation and/or one of its subsidiaries. All rights reserved.

Patient Portal

myTuftsMed is our new online patient portal that provides you with access to your medical information in one place. MyTuftsMed can be accessed online or from your mobile device providing a convenient way to manage your health care needs from wherever you are.

With myTuftsMed, you can:

  1. View your health information including your medications, test results, scheduled appointments, medical bills even if you have multiple doctors in different locations.
  2. Make appointments at your convenience, complete pre-visit forms and medical questionnaires and find care or an emergency room.
  3. Connect with a doctor no matter where you are.
  4. Keep track of your children’s and family members’ medical care, view upcoming appointments, book visits and review test results.
  5. Check in on family members who need extra help, all from your private account.


Your privacy is important to us. Learn more about ourwebsite privacy policy. X