A 2-year-old old boy presents with pruritis and xerosis of the skin. Facial pallor is noted. A diagnosis of seborrheic dermatitis was made at age 18 months because of the presence of retention hyperkeratosis on the scalp; causes of immunodeficiency were ruled out. Lesions have now developed on the cheeks and the legs. Parents report that that pruritis has been present on and off since infancy, and over the past few days, this symptom has led to sleep disturbance. There is a family history of asthma.