Cold sore

The Cold sore - A small skin blister, usually around the mouth, commonly caused by a strain of the herpes simplex virus called HSV1 (herpes simplex virus type 1).

The first attack of the virus may be symptomless or may cause a flu-like illness with painful mouth and lip ulcers called gingivostomatis. The virus then lies dormant in nerve cells, but may occasionally be reactivated and cause cold sores.

Reactivation may occur after exposure to hot sunshine or a cold wind, during a common cold or other infection, or in women around the time of their menstrual periods. Prolonged attacks can occur in people with reduced immunity to infection due to illness or treatment with immunosuppressant drugs.

In many cases, an outbreak of cold sores is preceded by tingling in the lips, followed by the formation of small blisters that enlarge, causing itching and soreness. Within a few days they burst and become encrusted. Most disappear within a week. The antiviral drug aciclovir in a cream may prevent cold sores if used at the first sign of tingling.