Hair analysis receives a large amount of academic and commercial interest for wide-ranging applications. However, in many instances, especially for elemental or 'mineral' analysis, the degree of success of analytical interpretation has been quite minimal with respect to the extent of such endeavors. In this critical review we address the questions surrounding hair analysis with specific intent of discovering what hair concentrations can actually relate to in a biogenic sense. This is done from a chemistry perspective to explain why and how elements are incorporated into hair and their meaning. This includes an overview of variables attributed to altering hair concentrations, such as age, gender, melanin content, and other less reported factors. Hair elemental concentrations are reviewed with regard to morbidity, with specific examples of disease related effects summarized. The application of hair analysis for epidemiology and etiology studies is enforced. A section is dedicated specifically to the area of population studies with regards to mercury, which highlights how endogenous and exogenous incorporation relies on species dependant metabolism and metabolic products. Many of the considerations are relevant to other areas of interest in hair analysis, such as for drug and isotopic analysis. Inclusion of a table of elemental concentrations in hair should act as a valuable reference (298 references).