A 4-year-old girl was evaluated for hair loss of a few weeks' duration. History of the present illness, medical history, and review of systems were obtained from the parents, who described progressive diffuse hair loss with hair dryness and brittleness, with no change in the child's eating habits or any other unusual symptoms. No fever, weight loss, diarrhea, vomiting, abdominal pain, chronic cough, dyspnea, change in appetite, change in bowel habit, or urinary symptoms were noted. On further questioning, her nutritional history revealed that she always favored cow's milk in her diet. The patient has been healthy with no significant medical history, surgical history, psychiatric history, or history of hospitalization. She was taking no medications. Her mother's pregnancy and the child's birth history were uneventful. The child was up-to-date on her vaccinations. Her physical examination showed a healthy-appearing child who was at 50% on the height chart and 70% on the weight growth chart. She was afebrile with a respiratory rate of 24 breaths per minute, pulse rate of 110 beats per minute, and pulse oximetry of 99% on room air. Skin examination revealed interstitial diffuse patchy alopecia with very dry hair and nonscarred, normal-appearing scalp. The hair pull test was normal, with 4 hairs extracted. Results of examination of her eyes (including visual acuity) and lungs were normal, and no abnormalities were found on heart, abdominal, musculoskeletal, and neurologic examinations. Laboratory workup showed normal electrolytes, blood urea nitrogen, creatinine, and blood sugar levels. Her complete blood cell count with differential was normal, ferritin concentration level was 110 ng/mL (reference, 40-200 ng/mL), iron level was 75 microg/dL (reference, 35-175 microg/dL), and total iron-binding capacity was 310 microg/dL (reference, 245-400 microg/dL). Levels of liver enzymes, total bilirubin, serum protein, and albumin were normal, as were the results of urinalysis. Thyroid function test results were normal and levels of vitamins A and D were also normal. Low levels of serum zinc were measured repeatedly at 48 and 61 microg/dL (reference, 66-144 microg/dL) at 2 different laboratories. She was started on zinc supplement (50 mg daily) for 6 months and her diet was modified. The hair loss stopped in 3 weeks. Follow-up in 4 months showed no evidence of alopecia, with normal-looking hair.