Hair shafts may stock up certain poisons for lifetime, even decades, after death, which can from time to time be identified with the use of an atomic absorption spectrophotometer. In recent years, a University of Toronto laboratory initiated the use of neonatal hair to show its contact to drugs during pregnancy. Drugs such as cocaine, methamphetamine, heroin, etc., mount up in the neonatal hair during its growth and thus serve as a long term ‘memory’ of what happened during fetal life. The hair analysis method used by Dr. G. Koren's research group transformed the analysis of in utero exposure to drugs.

Hair analysis is nothing but the chemical analysis of a hair sample. Hair may be considered for traditional purposes when blood and urine are no longer expected to hold a particular impurity, typically a year or less. Its most extensively accepted use is in the field of forensic toxicology and, more and more, environmental toxicology. Quite a few substitute medicine fields also use a variety of hair analyses for environmental toxicology but these uses are controversial, developing and not standardized.