A 6-year-old boy is referred to dermatology by his pediatrician for an “infection” unresponsive to two courses of oral antibiotics. The problem began two and a half weeks ago, when the patient noticed intense itching on the anterior tibial area of the left leg. The patient’s mother treated the rash with triple antibiotic ointment, but the problem worsened, so she took him to the pediatrician. Despite two courses of antibiotics, the area continued to itch to the point that the child could hardly sleep, but there has been no associated fever, pain, or malaise. The child is apparently healthy in other respects.

The child is afebrile and in no acute distress. Inspection of the affected area reveals a mass of confluent blisters covering most of the lower two thirds of the left anterior tibial area. Some of the blisters have broken and are draining clear fluid. There is no redness, no increased warmth, and no tenderness on palpation. The boy’s mother is seen reapplying the triple antibiotic ointment after the examination, prior to changing his dressing.

Given the facts as presented, the most likely diagnosis is: