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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, 9 out of 10 older adults have been exposed to HSV. Not everyone who is exposed to the virus will develop cold sores.
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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:
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.
Cold sores. Nemours Kids Health website. Available at: http://kidshealth.org/parent/infections/common/cold_sores.html. Accessed January 29, 2021.
Herpes simplex. American Academy of Dermatology website. Available at: https://www.aad.org/public/diseases/contagious-skin-diseases/herpes-simplex. Accessed January 29, 2021.
Oral herpes. EBSCO DynaMed website. Available at: http://www.dynamed.com/topics/dmp~AN~T115104/Oral-herpes. Accessed January 29, 2021.
Last reviewed March 2020 by EBSCO Medical Review Board David L. Horn, MD, FACP Last Updated: 1/29/2021