Your hair grows between 2 to 6 years before falling. During that time, the shaft absorbs chemicals, drugs, or any substance that you consume in that period. Toxic elements, such as mercury, can be 200 times more concentrated in your hair than in urine or blood.
Unlike blood, the levels of elements in the hair are not regulated by homeostatic mechanisms, which means a process of natural balance in your body that allows you to keep the internal conditions of your body stable. Therefore, your blood regulates these levels and does not let you know how many toxic metals are in your system.
Changes in the levels of elements in the hair often appear before they appear in the blood. Therefore, hair is ideal for detecting metal poisoning in your body.