The biologic bases for using hair and nail for analyses of trace elements.

Sampling of human beings for trace element content can be a complex and costly procedure. The use of hair and nails simplifies the process and it is for this reason that such samples are extensively used. The primary consideration, however, is not how easily the samples can be collected nor even how accurately trace elements can be measured in hair and nails; rather, it is what do the values mean, i.e., to what extent does the measured level reflect the concentration and/or activity of the element in other parts of the body? The structure and histogenesis of hair and nails are discussed in relation to mechanisms by which trace elements are incorporated into these tissues. Problems of contamination in vivo are also considered. A résumé of current literature is presented, considering the trace elements that are appropriate for measurement in samples of human hair and nail and some of the problems involved in analysis.