The biopsy specimen showed focal spongiosis associated with scattered apoptotic keratinocytes, with no evidence of vacuolar degeneration or satellite cell necrosis. The dermis contained a diffuse mixed inflammatory infiltrate, which was most pronounced around the adnexa. Serologic abnormalities included an elevated white blood cell count of 47 100/μL (reference range, 6900-15 700/μL) (to convert to ×109/L, multiply by 0.001) with 31% eosinophils. IgE level was elevated to 90 IU/mL (reference range, 0-8 IU/mL), and IgG level was reduced to 41 mg/dL (reference range, 188-536 mg/dL) (to convert to grams per liter, multiply by 0.01). The lymphocytes exhibited no proliferative response to mitogens. A bone marrow biopsy specimen was normocellular but displayed mild erythroid hyperplasia, eosinophilia, and granulocyte hypoplasia. No mutations in RAG1, RAG2, IL7R, and ZAP70 genes were identified; however, a hypomorphic missense mutation of the common gamma gene was discovered. Ultimately, X-linked recessive severe combined immunodeficiency disorder was diagnosed. The patient underwent a bone marrow transplant, and 2 months later his cutaneous eruption abated and hair regrew.