Cold sores are the most common clinical manifestation of herpes simplex virus (HSV) infection, with blisters or sores around the mouth, lips, nose or chin.
The vast majority of cases are caused by HSV type 1 (HSV-1), although HSV type 2 (HSV-2) infection has also been reported, and with increasing frequency. HSV-1 is mainly transmitted by contact with infected oral secretions or active lesions of other patients. In contrast, HSV-2 is transmitted mainly by orogenital contact and is rare in children.
Primary HSV-1 infection usually occurs in childhood, with a peak between 2-3 years of age, and most infections are mild or subclinical. The virus usually remains latent until a new outbreak is triggered by common factors such as fever, stress, ultraviolet (UV) radiation, sun exposure, surgical trauma, immunotherapy or hormonal changes.
Approximately one third of children acquire a primary HSV-1 infection before the age of 5 years. About 2.5 out of 1000 people are affected with outbreaks in a given year, and 30% of affected patients suffer relapses. Most patients with recurrent cold sores experience fewer than 3 episodes per year, but 5-10% of patients experience more than 6 episodes.
During the precursor phase, symptoms of pain, tingling, irritation, numbness or burning may appear in the affected area, followed by the appearance of vesicles. The rupture of the vesicle leads to the formation of a soft crust which is later replaced by a hard crust. Periodically, the scab subsides and falls off, allowing the lesion to heal completely (10-14 days) without scarring.
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