Phenylketonuria is characterized by a specific facial appearance, primarily presenting with pale skin and yellow hair. Some affected children may develop eczema due to a disruption in melanin synthesis, which results in a distinctive skin color. Additionally, there are neuropsychiatric abnormalities, such as intellectual disability, increased excitability, and heightened muscle tone. The urine of patients has a plastic-like smell, largely because phenylketonuria is a hereditary metabolic disease. Newborns exhibit hyperphenylalaninemia, but as harmful metabolites of phenylalanine are not present in high concentrations before feeding begins, initial conditions at birth are often normal. However, as diet is introduced and metabolite concentrations increase, specific clinical symptoms, including severe cases of epileptic seizures manifested as infantile spasms, nodding seizures, or other forms, become evident. Therefore, dietary management is essential in treatment.