Cold sores are blisters on the lips and the edge of the mouth that are caused by an infection with the herpes simplex virus (HSV).
Cold sore blisters usually break open, weep clear fluid, and then crust over and disappear after a few days.
Other symptoms may include:
You may not develop cold sores when you are first infected with HSV. If cold sores do develop when you are first infected, they may be more severe than in later outbreaks. During the first outbreak of cold sores, the blisters may spread to any part of the mouth.
After you become infected, HSV remains in your body and may cause cold sores to return throughout your lifetime (recurrent cold sores).
Recurrent cold sores usually develop where facial skin and the lip meet. About 6 to 48 hours before a cold sore is visible, you may feel tingling, burning, itching, numbness, tenderness, or pain in the affected area. This is called the prodromal stage.
Some common triggers that cause cold sores to return include:
People who have weakened immune systems are more likely than those with strong immune systems to have longer or more severe outbreaks of cold sores. HSV infection may be life-threatening in certain people who have weak immune systems.
Who is at greatest risk for developing cold sores?
Anyone who is exposed to the herpes simplex virus (HSV) is at risk for developing cold sores. But many people have the virus and may never develop cold sores.
People who have weakened immune systems are at an increased risk for having more severe and longer-lasting outbreaks of cold sores.
One form of HSV infection is seen most often in children 1 to 3 years old. This type of HSV infection (primary herpesstomatitis) can cause a high fever and blisters throughout the mouth, which can interfere with the ability to eat. It can be serious in children-they can get quite sick from this illness, although they usually recover without any long-term problems.