A 7-month-old previously healthy boy presents with a diffuse rash. Three months ago he developed an erythematous perioral rash that spread to his trunk and extremities. The rash persisted despite treatment with numerous corticosteroid creams, antibiotic courses, and antifungal treatments. The rash is not pruritic or painful, and he has been afebrile. He has also had hair loss.

The boy has no history of diarrhea, viral respiratory tract infections, acute otitis media, or other rashes. He is growing and developing appropriately and is up-to-date on his immunizations. He breastfeeds without difficulty and in the last month has begun to eat a small amount of soft, age-appropriate foods. His general skin care consists of three to four baths per week with lukewarm water. He is moisturized with petroleum immediately following his baths. His family has been trying tar shampoo and uses fragrance-free laundry detergent.

On physical examination, his vital signs are...

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