Cold sore, also called a fever blister, is a small blister caused by a virus called herpes simplex virus. Cold sores can occur anywhere on the body. However, they appear mostly on the face, especially on or near the lips. The virus spreads chiefly through contact with the saliva of an infected person. The virus remains dormant (inactive) in the sensory nerves of the skin. The dormant virus usually causes no symptoms. But certain conditions, or triggers, can reactivate it, producing new cold sores. Common triggers include fever, injury, emotional stress, sunlight, and menstruation.
Once the virus is triggered, a person may experience itching, tingling, pain, and redness of the skin. One or more blisters appear sometime later. They soon break open, and a yellowish crust forms over them. The sores heal two to seven days after the blisters break open. Cold sores always occur in the same place on the skin, above the nerve where the virus otherwise lies dormant.
Doctors prescribe antiviral drugs, such as acyclovir and valacyclovir, as treatment for cold sores. These drugs hinder outbreaks but do not cure the virus. A topical skin cream marketed under the name Abreva can also help hinder outbreaks in some people.
