A 12-day-old girl was evaluated for a rash. The patient was born at 40 weeks' gestation via normal spontaneous vaginal delivery to a woman of Vietnamese descent. No complications occurred during the pregnancy or delivery. She was discharged on the third day of life. She drank 90 mL of infant formula (Enfamil) every 3 hours, wet multiple diapers, and had no fussy behavior. She had no other significant illness, had no known drug allergies, and had received her hepatitis B vaccine at birth.