Hair analysis may refer to the chemical analysis of a hair sample, but can also refer to microscopic analysis or comparison. Chemical hair analysis may be considered for retrospective purposes when blood and urine are no longer expected to contain a particular contaminant, typically three months or less.

Its most widely accepted use is in the fields of forensic toxicology, in pre-employment drug testing and, increasingly, in environmental toxicology. Several alternative medicine fields also use various hair analyses for environmental toxicology, but these uses are controversial, evolving, and not standardized.

Microscopic hair analysis has traditionally been used in forensics as well. Analysts examine a number of different characteristics of hairs under a microscope, usually comparing hair taken from a crime scene and hair taken from a suspect. It is still acknowledged as a useful technique for confirming that hairs do not match. But DNA testing of evidence has overturned many convictions that relied on hair analysis. Since 2012, the Department of Justice has conducted a study of cases in which hair analysis testimony was given by its agents, and found that a high proportion of testimony could not be supported by the state of science of hair analysis.

Biology of hair

Hair consists of various characteristics that can be of use in a forensic examination and analysis. To the core, hair is composed of keratin, water, minerals, and lipids. Hair consist of two distinctions parts, the hair shaft and the hair root. The shaft is composed of 3 layers, first being the medulla which is the inner core (if present), the second being the cortex which is the middle layer composed of multiple cells, and then lastly the cuticle which is the outer layer. Hair analysis is less invasive than a blood test, if not quite as universally applicable. In this context, it has been reliably used to determine compliance with therapeutic drug regimes or to check the accuracy of a witness statement that an illicit drug has not been taken. Hair testing is an increasingly common method of assessment in substance misuse, particularly in legal proceedings, or in any situation where a subject may have decided not to tell the entire truth about his or her substance-using history. Post-mortem hair sample analysis can also be performed, to allow for determination of long-term drug use or poisoning. It is also used by employers, who test their employees.

Hair analysis has the virtue of showing a 'history' of drug use due to hair's slow growth. Urine analysis might detect drugs taken in the past 2–3 days; hair analysis can sometimes detect use as far as 90 days, although certain cosmetic treatments (e.g. dyeing hair) can interfere with this.

Notably, basic drugs get incorporated into hair to a greater extent than neutral or acidic drugs, e.g. amphetamines and cocaine

are present in higher concentrations in hair compared with

benzodiazepines and cannabinoids.

Large-scale drug screening (or urine, hair and other samples) is usually done using enzyme-linked immunosorbent assays (ELISA). Positive ELISA findings are followed by confirmatory testing with liquid chromatography–mass spectrometry (LC-MS) or gas chromatography–mass spectrometry (GC-MS).

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In December 1995 the Society of Hair Testing was founded to promote the research in hair testing technologies in forensic, clinical and occupational sciences, to develop international proficiency tests, to organize meetings and workshops, and to encourage the scientific cooperation and exchanges among members. The Board of the Society of Hair Testing agreed upon the latest version of a Consensus in Sevilla, Spain, in 2004. -->

Microscopic hair analysis in forensics

Microscopic hair analysis consists of the comparison of several strands of hair under a microscope and determining if the physical characteristics of each individual hairs are consistent with each other or not. It was accepted as a forensic science by the 1950s.

In hair analysis, it is a basic requirement and a needed skill to be able to distinguish between what is human hair and what is animal or non human hair. To firstly determine the nature of these hairs it is necessary to do a visual examination of the hairs following with a low-power microscopic examination. When comparing the medulla if its present, central core of the hair shaft there is a measurement between the relative diameter of the medulla when compared to the overall hair diameter which is the medullary index. DNA analysis and Chemical analysis are more accepted in the court of law as they are more accurate in results and can determine a conclusive answer. U.S. Department of Justice guidelines cite that <nowiki></nowiki>hair comparison has been demonstrated to be a valid and reliable scientific methodology, alt ought microscopic hair comparison cannot lead to person identification and it is crucial that this limitation be conveyed. thumb|The image depicts different properties that make up a strand of hair.

Skepticism about the stronger claims used by witnesses in the 1970s and 1980s existed at the time. Researchers said in 1974 that the whole process was inherently subjective, and the FBI wrote in 1984 that hair analysis cannot positively match one single person.

In 1994, the Justice Department created a task force which would eventually review 6,000 cases by 2004, focusing on the work of one particularly zealous examiner, Michael Malone. The study showed that 11% of hair analysis "matches" were contradicted by DNA analysis. As the set of cases analyzed was one which would be expected to favor matches strongly in any case – only hair of individuals the police already believed to be potential suspects was sent in – this error rate was considered to be extremely high. Combined with a witness's identification in a line-up (another technique which modern research has shown to be much less reliable than previously thought), Odom was sentenced to twenty or more years in jail. DNA analysis, however, proved that Odom was entirely innocent.

In a similar case, Santae Tribble was convicted in 1979 at the age of 17 in Washington, DC of murder due to FBI testimony in a hair analysis match of hair found at the scene. But he had three witnesses who gave him an alibi for the time when the crime was committed. The prosecutor overstated the reliability of hair analysis in identifying a single person, saying in his closing statement that "There is one chance, perhaps for all we know, in 10 million that it could [be] someone else's hair."

The outcry from defense attorneys about the unreliability of hair analysis and overstatement by FBI experts has resulted in the FBI conducting a review of disputed hair analysis matches since 2012. Due to what it found, in July 2013 the Justice department began an "unprecedented" review of older cases involving hair analysis, examining more than 21,000 cases referred to the FBI Lab's hair unit from 1982 through 1999.

By 2015, these cases included as many as 32 death penalty convictions, in which FBI experts may have exaggerated the reliability of hair analysis in their testimony and affected the verdict. Of these, 14 persons have been executed or died in prison. In 2015, DOJ released findings on 268 trials examined so far in which hair analysis was used (the review was still in progress). The review concluded that in 257 of these 268 trials (95 percent), the analysts gave flawed testimony in court that overstated the accuracy of the findings in favor of the prosecution. About 1200 cases remain to be examined. The department emphasized its commitment to following up on these cases to correct any wrongs, saying that they "are committed to ensuring that affected defendants are notified of past errors and that justice is done in every instance. The department and the FBI are also committed to ensuring the accuracy of future hair analysis, as well as the application of all disciplines of forensic science."

In 2017, new Attorney General Jeff Sessions, appointed by President Donald Trump, announced that this investigation would be suspended, at the same time that he announced the end of a forensic science commission that had been working to establish standards on several tests and to improve accuracy; it was a "partnership with independent scientists to raise forensic science standards". Independent scientists, prosecutors, defense counsel and judges criticized ending the commission, saying that the criminal justice system needed to rely on the best science.

As of late 2019, 75 people who were convicted of a crime based on microscopic hair comparison were subsequently exonerated. Another notable case that received media attention since was Anthony Broadwater, who had been convicted of raping Alice Sebold in 1982, and was formally exonerated in 2021 after finishing his time in 1998. The only physical evidence the prosecution offered in 1982 was a hair analysis that was "consistent" with Broadwater. More alarmingly, the only reason the case was re-examined was the unusual fact that Sebold had written an extensive memoir of her experiences (Lucky), which allowed later investigators to uncover major problems with the case.

In environmental toxicology

Analysis of hair samples has many advantages as a preliminary screening method for the presence of toxic substances deleterious to health after exposures in air, dust, sediment, soil and water, food and toxins in the environment. The advantages of hair analysis include the non-invasiveness, low cost, and the ability to measure a large number of, potentially interacting, toxic and biologically essential elements. Hence, head hair analysis is increasingly being used as a preliminary test to see whether individuals have absorbed poisons linked to behavioral or health problems.

Occupational, environmental and alternative medicine

Hair analysis has been used in occupational, environmental and some branches of alternative medicine as a method of investigation to assist screening and/or diagnosis. The hair is sampled, processed and analyzed, studying the levels of mineral and metals in the hair sample. Using the results, as part of a proper examination or test protocol, practitioners screen for toxic exposure and heavy metal poisoning. Some advocates claim that they can also diagnose mineral deficiencies and that people with autism have unusual hair mineral contents. These uses are often controversial, and the American Medical Association states, "The AMA opposes chemical analysis of the hair as a determinant of the need for medical therapy and supports informing the American public and appropriate governmental agencies of this unproven practice and its potential for health care fraud."

A recent review of scientific literature by Dr Kempson highlighted analysis of metals/minerals in hair can be applied in large population studies for researching epidemiology and groups of chronically exposed populations, however any attempt to provide a diagnosis based on hair for an individual is not possible. An exception to this can be in advanced analyses for acute poisoning.

Literature

  • Pragst F., Balikova M.A.: State of the art in hair analysis for detection of drugs and alcohol abuse; Clinica Chimic Acta 370 2006 17–49.
  • Auwärter V.: Fettsäureethylester als Marker exzessiven Alkoholkonsums – Analytische Bestimmung im Haar und in Hautoberflächenlipiden mittels Headspace-Festphasenmikroextraktion und Gaschromatographie-Massenspektrometrie. Dissertation Humboldt-Universität Berlin 2006.

References

Bibliography

  • Henderson, G.L., Harkey, M.R., Jones, R.T., "Analysis of Hair for Cocaine", in (eds. Edward. J. Cone, Ph.D., Michael. J. Welch, Ph.D., and M. Beth Grigson Babecki, M.A.), "Hair Testing for Drugs of Abuse: International Research on Standards and Technology", 1995, pp.&nbsp;91–120. NIH Publication No. 95-3727.
  • Cary T. Oien, Unit Chief, FBI Lab, "Forensic Hair Comparison: Background Information for Interpretation", Forensic Science Communications, April 2009, Volume 11, Number 2
  • Society of Hair Testing
  • "Hair Drug Testing Bibliography", Criminology, Florida State University