Cold sores, which are also called fever blisters, are small, highly contagious skin ulcerations caused by herpes simplex virus (HSV) infection. A cold sores fact sheet published by the Better Health Channel explains that approximately 90 percent of adults have HSV, but many do not experience symptoms. An estimate one-third of people with HSV develop cold sores, which can cause a number of side effects.
Itching or Tingling
If you have HSV, cold sore development may be instigated by emotional stress, an alternate illness, injury to the skin or fever. Before developing the characteristic skin lesion associated with cold sores, you may experience an itching or tingling sensation at a specific site, such as the lip or chin. Such sensations typically occur one to three days before the cold sore appears on the skin.
Blister formation typically occurs two to three days after the onset of the itching or tingling sensations. These blisters may form on any region of the body in people with HSV, but they most commonly occur on the lips or the skin around the mouth, chin or nose. Rarely, these blisters may form within your mouth along your gum line. If this occurs, the appearance of blisters within the mouth should not be confused with canker sores, a condition that can cause similar symptoms within the mouth but is not contagious or associated with HSV infection. Cold sore blisters may become filled with fluid or pus and can be uncomfortable.
Pain or Tenderness
Cold sore blister formation can cause pain or tenderness to develop at the site of the skin lesion. The infection may cause the blister to appear red or inflamed.
After a day or two, the cold sore blister will burst and lead to ulcer formation. The fluid within these skin lesions will dry out, and a yellow or white crust will form over the skin ulceration. During this stage of cold sore progression, you may experience a burning or painful sensation at the site of the skin lesion. If you have a cold sore, you may be embarrassed or reluctant to go out in public, especially if the skin ulceration is on your face. Approximately one week after the initial onset of itching or tingling symptoms, a scab will likely form over the cold sore, which means that the infection has begun to heal. The cold sore scab will flake off two to three days after it forms, indicating that the skin infection has healed.