A 2-year-old boy was referred to the dermatology clinic with an 8-month history of rash, hair loss, and watery diarrhea. The child had been exclusively breast-fed until 6 months of age, at which time a vegetarian solid-food diet of produce and natural grains had been introduced. When the child was weaned from breast milk to cow’s milk at 16 months of age, the symptoms had started. On examination, the child was irritable; he had angular cheilitis, alopecia, and erosions with crusted borders across the face and scalp and around the mouth, eyes, and ears (Panels A and B). The rash also involved the perianal region, trunk, and all four limbs (Panel C). Laboratory testing showed a serum zinc level of 0.32 μg per milliliter (reference range, 0.65 to 1.10) and a low alkaline phosphatase level. Zinc is a cofactor for alkaline phosphatase activity, and therefore a low alkaline phosphatase level may be seen in a patient with zinc deficiency. A diagnosis of dietary zinc deficiency–associated dermatitis was made. Oral zinc supplementation and dietary changes were recommended. At a 3-week follow-up visit, the alopecia and dermatitis had abated (Panel D). When zinc supplementation was stopped 3 months later, the symptoms did not recur.