Phenylketonuria does not easily cause a cold, as a cold is a type of infectious disease mainly caused by various pathogen infections and stimuli, leading to symptoms such as cough, fever, and runny nose. Phenylketonuria is a common amino acid metabolism disorder caused by a deficiency of the enzyme required for phenylalanine to convert into tyrosine, resulting in excessive excretion of phenylalanine in urine. This disease is a recessive hereditary disorder, which can lead to intellectual disability, neuropsychiatric symptoms, and pigment loss. Due to the lack of melanin, affected children often present with yellow hair, pale skin and sclera, and their urine has a mousy odor. They may also suffer from eczema, vomiting, and diarrhea. Phenylketonuria is one of the few treatable hereditary metabolic diseases, so it generally does not cause symptoms of a cold.