Deficiency of certain trace elements. For example, iron deficiency anemia can lead to malnutrition of hair; copper deficiency can reduce the function of tyrosinase and affect the metabolism of melanin; zinc deficiency will affect the development and growth of cells, the hair will naturally yellow. In terms of the physiological characteristics of hair, each hair root has a hair gallery, in its surrounding there are hair mother keratinized cells and hair mother pigment cells, once the function of these cells is disturbed or damaged, black hair will turn yellow. What is the diagnosis of yellowish hair? 1, dry hair: dry hair, also known as dry hair, hair with less hair, etc.. Due to the lack of moisturizing hair and lusterless, or even dry and scorched, easy to fold down, often accompanied by dry skin. The main component of hair is protein containing sulfur amino acids, therefore, appropriate amount of protein-rich food such as fish, lean pork, milk, dairy products and soy products should be consumed daily. Dry hair is caused by a dry scalp (insufficient sebum production in the scalp). Experts recommend the intake of vitamin A to hydrate the hair (be careful of the prescribed intake). Frequent combing of hair will accelerate blood circulation and sebum secretion. 2, hair abnormalities: hair abnormalities can generally be divided into: hair loss, baldness, hirsutism, hair discoloration, hair deformity, hair degeneration. The etiology can be divided into congenital, hereditary, primary, acquired, medical and traumatic. 3, hair color light and brown: Phenylketonuria patients due to tyrosinase inhibition, so that the reduction of melanin synthesis, so the affected children’s hair color light and brown. Phenylketonuria is a hereditary disease caused by the lack or reduced activity of hepatic phenylalanine hydroxylase, resulting in impaired phenylalanine metabolism. It is more common in inherited amino acid metabolism deficiency disorders.