Deficiency of certain trace elements. For example, iron deficiency anemia will lead to malnutrition of hair; copper deficiency will reduce the function of tyrosinase and affect the metabolism of melanin; zinc deficiency will affect the development and growth of cells, and hair will naturally become 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. 1, the factors of heredity; 2, heavy iron deficiency anemia and major illness, etc., resulting in the reduction of melanin in the body, so that the basic substance of black hair lack, black hair gradually become yellowish brown or yellowish; 3, a high degree of malnutrition; 4, frequent perming, washing hair with alkaline water or washing powder; 5, low thyroid function. Washing hair too often or commonly used alkaline soap to wash hair, especially the use of excessive grease-removing strong shampoo, can make the sebum with the role of hair protection removed. At the same time alkaline shampoo has a strong stimulation to the epithelial cells of the scalp, making it excessive, leading to yellowing of the hair. Some people think it is related to eating too much grain or fat. This is because these substances tend to produce lactic acid or carbonic acid, etc. in the body. When there is too much acid, the hair gradually turns yellow. It is caused by a certain disease. For example, when you have systemic scleroderma and systemic lupus erythematosus, your hair will not only turn yellow but also fall out in large quantities.