A man in his 60s presented with new-onset bullae and erosions over sun-exposed areas and bony prominences. His medical history was relevant for acute myeloid leukemia, for which he had received an allogeneic stem cell transplant that was complicated by biopsy-proven grade 3 cutaneous and grade 2 gastrointestinal graft-vs-host disease. As part of his posttransplant infectious prophylaxis, the patient had been prescribed valacyclovir hydrochloride, voriconazole, and trimethoprim/sulfamethoxazole. He was also taking tacrolimus hydrate and prednisone for treatment of his graft-vs-host disease. The patient reported fishing outdoors on a sunny day a few days prior to the onset of these skin lesions. On physical examination, the patient’s skin was diffusely tan and there were flaccid bullae and erosions on the bilateral dorsal hands, elbows, and knees (Figure, A). A punch biopsy specimen from a bulla from the upper extremity was obtained (Figure, B).