In terms of the physiological characteristics of hair, there is a hair gallery at the root of each hair, and there are hair mother keratinized cells and hair mother pigment cells around it. Once the function of these cells is disturbed or damaged, the black hair will turn yellow. Washing hair too often or using alkaline soap to wash hair, especially using too many shampoos with strong grease removal, can make the sebum with the role of hair protection removed. At the same time alkaline shampoo has a strong stimulation of 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 some kind of disease. Which items should be checked to check yellowish hair? 1.Blood The blood sample should be collected from a vein or peripheral blood. The content of trace elements in the human body is low and is susceptible to various kinds of contamination during the collection of samples, so trace element blood samples need to be collected with extra care. In addition to the requirements for sample collection made by the “Technical Specification for Blood Lead Clinical Testing” of the Ministry of Health, special test tubes for trace elements that have been qualified after regular sampling should be used, and the tubes should be immediately sealed with inert and non-contaminating materials to eliminate the influence of the containers themselves on the test results. Blood test is easy to contaminate and cause cross infection, sampling is not convenient, reflecting the body trace element status in a short period of time, and is influenced by diet and disease aspects, and is only used as clinical guidance. 2.Hair Human hair includes hair, axillary hair, beard, chest hair, etc. Among them, hair testing is the most widely used: (1) Hair samples are easy to take and easy to preserve. (2) for trace elements, the content of hair due to the accumulation of reasons than other parts of the body such as blood, saliva, urine content is high, and more stable, easier to analyze. (3) Hair can reflect the nutritional status of trace elements in the past few weeks to months, and thus can truly reflect the storage status of trace elements. (4) The protein structure of hair can bind to elements in the environment such as water and atmosphere, and its binding power varies with various trace elements, so trace elements in hair can also be used as an indicator of environmental pollution. It also shows that hair testing does not represent the true level of trace elements in the body. Hair testing is generally not used in medical institutions.