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Cold sores are small, painful, fluid-filled blisters. They are also known as fever blisters. The blisters occur most often on the lips. They may also occur in other places such as the mouth, nose, chin, cheeks, and throat, or other areas of the skin.

Cold sores are often caused by the herpes simplex type 1 virus (HSV-1). Less often, however, they can be caused by herpes simplex type 2 (HSV-2). HSV-2 is the virus that most often causes genital herpes. Having a herpes simplex virus (HSV) infection around the mouth is very common. In fact, nine out of ten older adults have been exposed to HSV. Not everyone who is exposed to the virus will develop cold sores.

Herpes Simplex on the Lips


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The virus is spread through skin-to-skin contact or from contact with infected saliva. Sores do not have to be present for the virus to be spread. Spread may happen:

  • Through kissing and other close contact
  • Through sharing eating utensils, razors, towels, or other personal items
  • Sharing food or drink
  • Contact with saliva containing HSV

When HSV gets on the skin around the mouth, it invades nerves in the area. It then remains there quietly, for 2-20 days. Then the first outbreak may occur. This outbreak can cause blistering across the lips, tongue, and inside of the mouth. You may also have a body-wide, flu-like illness. It can occur with fever, general aches and pains, and swollen lymph glands.

The outbreak will last about 7-10 days. The virus then goes back into the nerves. It will remain there quietly until it is reactivated. This will cause a second outbreak. This outbreak will cause painful, blistering sores. They occur most often at the border of the colored part of the lip. These sores can last for up to 14 days. It is impossible to predict when these outbreaks may recur. Typically stress or illness may bring them on. They may also be brought on by sunlight, immune suppressants, or a woman's menstrual period. Some people have outbreaks regularly, while some never have another.

What are the risk factors for cold sores?
What are the symptoms of cold sores?
How are cold sores diagnosed?
What are the treatments for cold sores?
Are there screening tests for cold sores?
How can I reduce my risk of cold sores?
What questions should I ask my doctor?
What is it like to live with cold sores?
Where can I get more information about cold sores?

References:

Cold sores. Nemours Kids Health website. Available at: http://kidshealth.org/parent/infections/common/cold_sores.html. Updated October 2010. Accessed February 17, 2014.

Herpes labialis. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated January 30, 2014. Accessed February 17, 2014.

Herpes simplex. American Academy of Dermatology website. Available at: http://www.aad.org/dermatology-a-to-z/diseases-and-treatments/e---h/herpes-simplex. Accessed February 14, 2014.



Last reviewed February 2014 by David L Horn, MD, FACP

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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