A 6-year-old child with a history of primary herpes simplex has a recurrent infection. What is the most likely cause?

In the context of a 6-year-old child with a history of primary herpes simplex experiencing a recurrent infection, the most likely cause is herpes labialis. This condition is commonly known as cold sores and is triggered by reactivation of the herpes simplex virus, often HSV-1. Once a person is initially infected with the virus, it remains dormant in the nerve roots and can reactivate due to various factors such as stress, illness, or sunlight exposure, leading to recurrent outbreaks.

Herpes labialis specifically involves the lips and mouth area, presenting as painful vesicular lesions. Since the child has a documented history of primary herpes simplex, it is indicative that the herpes virus remains in the body and can re-emerge, particularly during times of lowered immunity or stress.

Other conditions, like hand-foot-and-mouth disease and chickenpox, stem from different viruses (coxsackievirus and varicella-zoster virus, respectively) and present with distinct symptoms and lesions that do not directly correlate to the recurrence of herpes simplex infections. Impetigo is a bacterial infection marked by pustules and crusting and does not relate to the viral infection history. Therefore, herpes labialis is the most apt cause of recurrent infections in this scenario.