Schema depicting how human hair appears in a scanning electron microscope
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 and, increasingly, 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.
In forensic toxicology
Hair analysis is used for the detection of many therapeutic drugs and recreational drugs, including cocaine, heroin, benzodiazepines and amphetamines. 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. It is also used by private 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 three days; hair analysis can sometimes detect use as far as a month, although certain cosmetic treatments (e.g. dyeing hair) can interfere with this. Hair analysis has the ability to measure a large number of potentially interacting elements, although that trait is shared with many other drug tests.
Microscopic hair analysis in forensics
Microscopic hair analysis is the science of comparing several strands of hair under a microscope and attempting to deduce if the strands 'match'. It was accepted as a forensic science by the 1950s. Researchers often monitored more than a dozen attributes, including pigment distribution and scale patterns. This technique has been used in criminal investigations to try to tie hair found at a crime scene, or other location of note, and confirm if the hair matches that of a suspect. While a simple hair color match might be consistent with a certain suspect having been at the scene – black hair at the scene when the suspect has black hair – microscopic hair analysis began to claim a stronger standard by the 1970s. Rather than merely "narrow the field" of possibilities, hair analysts claimed to be able to match a specific person, such that the hair could be 'proof' of a specific suspect's presence. While the typed reports often hedged the certainty of microscopic hair analysis, witnesses in court would not always be as modest. The manager of the Montana state crime lab testified there was a "1 in 10,000 chance" that hairs found at a crime scene did not come from the suspect in one case, for example.
Microscopic hair analysis has a long tradition of being used in crime fiction as well; it was originally popularized in the Sherlock Holmes series before being widely used by the police. Fictional TV programs involving police procedurals and detectives have continued to use it since, including Columbo, Quincy, ME, Dexter, and CSI.
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 the 1990s, DNA profiling was introduced as a key new technique into forensics investigations; it introduced a new level of certainty about matching suspects to evidence. DNA analysis of old cases from the 1970s and 80s, however, contradicted conclusions about a number of earlier matches on the basis of hair analysis.
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. These reviews came after reports that sloppy work by examiners at the FBI lab was producing unreliable forensic evidence in court trials. At first, these investigations were largely kept quiet; The Washington Post reported that "Instead of releasing those findings, they made them available only to the prosecutors in the affected cases." A study of FBI Laboratory hair analysis cases between 1996 and 2000 was released in 2002 by Max M. Houck and Bruce Budowle. 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.
Kirk L. Odom was convicted of rape in Washington, DC in 1982 by no physical evidence except microscopic hair analysis performed by the FBI Crime Laboratory. 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. While Odom had been released from prison in 2003, he was officially exonerated in 2012 and was paid a large settlement by the city.
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." DNA testing in January 2012, however, showed that the prosecution's key piece of evidence, the hair, did not in fact match the defendant. Tribble was fully exonerated in December 2012, having served 28 years in prison that resulted in severe health problems.
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.
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.
Detection of long-term elemental effects
The use of hair analysis appears to be valid for the measurement of lifelong, or long-term heavy metal burden, if not the measurement of general elemental analysis. Several studies, including the analysis of Ludwig van Beethoven's hair, have been conducted in conjunction with the National Institutes of Health and Centers for Disease Control and Prevention.
In a 1999 study on hair concentrations of calcium, iron, and zinc in pregnant women and effects of supplementation, it was concluded that "From the analyses, it was clear that hair concentrations of Ca, Fe, and Zn could reflect the effects of supplementation... Finally, it could be concluded that mineral element deficiencies might be convalesced by adequate compensations of mineral element nutrients."
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.
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