A 12-year-old boy presented with a 4-day history of rash that began on the trunk and spread to the face and extremities. He denied any skin pain or pruritus. There was no history of recent travel or illness, but he reported contact with a classmate who had painful oral sores. He denied malaise or decreased appetite. On physical examination, the patient was afebrile with normal vital signs. Examination of the skin revealed erythematous papulovesicles on the face, trunk, and extremities with prominent vesicles and bullae on his genitalia, buttocks, and posterior thighs (Figure, A). A skin biopsy specimen revealed subepidermal vesicles with focal reticular degeneration (Figure, B).