Phenylketonuria is a condition in which the hair color is light and brown due to the inhibition of tyrosinase, which reduces melanin synthesis. Phenylketonuria (PKU) is a genetic disorder in which phenylalanine metabolism is impaired due to a lack of or reduced activity of phenylalanine hydroxylase (PAH) in the liver, which is more common in inherited amino acid metabolism deficiencies. PKU is an inherited disorder, so newborns are born with hyperphenylalaninemia, but they have no clinical manifestations because they are not fed and their blood phenylalanine and its harmful metabolites are not at high concentrations. If a newborn is not screened for phenylketonuria, clinical symptoms gradually manifest themselves as the blood phenylalanine and its metabolites gradually rise with the prolongation of feeding. Genetic diseases are difficult to treat and have unsatisfactory outcomes, making prevention even more important. Preventive measures include avoiding marriage between close relatives, promoting genetic counseling, carrier genetic testing and prenatal diagnosis and selective abortion to prevent the birth of affected children. Promote breastfeeding. Early detection of carriers of phenylketonuria and popularization of ferric chloride diapers to enable early detection and early treatment of infants who have developed the disease are important ways to prevent low intelligence.