Review Question - QID 215046

A 46-year-old farmer presents to the office for a follow-up visit. He was seen 4 days ago for a new lesion on his arm that had been present for 1 week prior to that visit. A photograph of the lesion is shown in Figure A. At that time, he was prescribed treatment for the lesion and instructed to follow up as necessary. Today, he reports that he became sunburned this morning within an hour of beginning his workday, despite wearing appropriate sunscreen. He has a medical history significant for type 2 diabetes mellitus that is controlled with metformin. He has no known medical allergies. He smokes 1 pack of cigarettes per day and denies alcohol or illicit drug use. His temperature is 98.6°F (37.0°C), blood pressure is 125/70 mmHg, pulse is 65/min, and respirations are 12/min. On exam, there is a blistering erythematous rash on the arms and shoulders. The previous skin lesion appears unchanged. Which of the following is the most likely explanation for the patient's new rash?