Inorganic constituents of hair are determined by the entry of substances from blood supply and to a lesser extent from external sources - making an ideal medium for analysis.
Hair used as one of the tissues of choice by the United States Environmental Protection Agency in determining toxic metal exposure with the following summary:- The milk, urine, saliva and sweat measure the component that is absorbed but excreted. The blood measures the component absorbed and temporarily in circulation before excretion and/or storage. The hair, nails and teeth are tissues in which trace minerals are sequestered and/or stored.
Since the structure of hair remains unchanged following growth, mineral content remains constant or fixed in the hair. These levels are not subject to change once that portion of hair is grown, so the analysis to accurately provides concentrations of minerals that have accumulated in the hair tissue over the hair growth period, approximately one to three months.
The mineral composition of hair directly reflects the mineral composition of the body's tissues in that region during hair growth. If a mineral deficiency or excess exists in the hair, it can directly indicate a mineral deficiency, excess or imbalance within surrounding tissues and the rest of the body. Essentially, hair is a recording filament that can reflect metabolic status over medium to long periods of time. Therefore as a simple non-invasive diagnostic tool, hair analysis can provide an overview of post nutritional and other metabolic events.