The Importance Of Hair As Biological Evidence In Forensic Science

In a criminal investigation, the finding of biological evidence such as hair is useful to establish the crime scene’s significance, to link a suspect to a weapon or the crime scene itself, to support witness statements, or even to link different areas of the crime scene.

hair - Biological Evidence

“A crime scene is a place where at least one criminal act occurred and where in specific and defined spaces and times, several actors are involved in certain dynamics driven by at least one motivation. It includes the area in which certain evidence can be recovered by forensic police and forensic scientists”.

During crime scene investigations, human hairs are one of the biological evidence which can be found and can lead operators to identify the perpetrator(s) of a specific crime.

In fact, human hair can easily be found on exhibits – both clothes and objects – near victims and/or in the crime area. The protective, detection, and thermal isolation functions of hair make them strongly present in almost all human populations, increasing the possibility of finding them everywhere, especially at crime scenes. Hair is one of the most common pieces of evidence or samples that crime scene operators and forensic biologists have to deal with during collection and examination. Therefore, they are a highly relevant type of biological evidence in forensics. 

The hair is the main component of the hair follicle commonly examined under a microscope, a long, thin cylinder of keratinized cells composed of three different cellular components: medulla, cortex, and cuticle. All the elements that constitute the hair originate from the hair follicle, a dynamic organ in which division, differentiation, and migration of cells into the various tissues occur.

DNA analyses are destructive and hair-consuming techniques. DNA is, in fact, particularly resistant to physical degradation phenomena and can be recovered – even years later – from very small fragments of any kind of biological material containing cells. A complete and detailed microscopic comparison with possible known sources of hair should be made before DNA analysis, as it is not always possible to do so afterward. 

When the collected human hair has the bulb, it has a sufficient number of cells for DNA identification.

From hair without the bulb, it is still possible to extract DNA from the stem – called mitochondrial DNA – although, in criminal proceedings, this is not always acceptable valid evidence, as the genetic material in the stem is minimal.

However, the extracted mitochondrial DNA can help subsequent criminological investigations to identify a subject, i.e. the offender who committed a specific crime.

A combination of mitochondrial DNA and comparison microscopy often helps to exclude or provide a stronger association than using only one technique.

A hair examination can also be useful to determine if the person has been poisoned or was under the influence of medication and/or drugs. This is possible because no active metabolism takes place in the hair, many ingredients are stored in it, thus providing a time window in which the person’s history of substance abuse can be traced.

Hair formations are a type of biological evidence that must be collected very carefully so as not to damage the bulb, i.e. the part containing the DNA potentially useful for forensic genetic analysis. In fact, they should only be collected if it is not possible to transport the entire finding, or if it is assumed to be lost due to moving the finding.

The acquisition of the single hair formation should be preferably performed with sterilized tweezers – better steel than single-use because of the electrostatic phenomena that can occur with contact with the hair formation – and then placed in a sterilized tube or container. This should be treated after as a finding and then ensured in a security bag with a seal.


Microscopic analysis of human hair can be used to perform a comparative analysis of suspects, focusing on rather well-known morphological features such as medulla, scales, cortex, cuticle, and pigmentation. Furthermore, the human hair bulb, found at the crime scene or on findings, can be used in forensic genetics examination to obtain a DNA match between the hair and the suspect or victim. In fact, only within the hair bulb are there nucleated cell traces that allow operators to extract DNA and perform a genetic profile.

The final significance of the analyses depends on the context in which the hair in question was found, regardless of whether the hair formations are compared under the microscope or subjected to mitochondrial DNA (mtDNA) sequencing.

Solving a case is a complex procedure, involving numerous experts and where each element has to be carefully considered and evaluated in relation to the other elements identified, be they of a material nature or from interviews.

Therefore, hair evidence is an important tool in forensic investigations because it can lead to species identification (whether it is human hair or not) and personal identification (through DNA analysis).

In order to understand the importance of hair as biological evidence in Forensic Science, at the Bio Forensics Research Centre I’m collaborating on a Research & Tech development series.

I performed a Pilot Human Hair study “Bulb morphology description in Forensic Biological examination”, which had the aim of performing a morphological description of human hair bulbs and their comparison using specific parameters; to try to understand if it could be possible to identify different clusters for identification of persons based on their different bulb’s characteristics.

Now we are carrying out a research study on the examination of hair, the aim of which is to cross-compare multiple knowledge from different research works on forensic hair examination in order to assess the evolution of the study and technology in this field and assess new perspectives of research and forensic applications.

As a future perspective, we would like to conduct an examination of the comparison between human and animal hair bulbs for species identification.


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  • Curtotti, D., and Saravo L., (2013). Handbook of crime scene investigation. Norms, techniques, science, logic. (Giappichelli Editore)
  • Montagna, P., and D’Orio, E. (2021). Handbook The specialist collection in Forensic Biology. (Herald Publisher)
  • Kintz P. (2017). Hair Analysis in Forensic Toxicology: An Updated Review with a Special Focus on Pitfalls. Current pharmaceutical design, 23(36), 5480–5486
  • Saferstein, R. (2001) Criminalistics: An Introduction to Forensic Science. Prentice Hall, Englewood, NJ
  • Skopp G. (2010) Postmortem toxicology. Forensic Sci Med Pathol Turco M., Lodeserto G., Bruscella M.r. (2016). Crime Analyst. Psychocriminological and investigative aspects. Primiceri editor

About The Author

Ms. Chiara Lucanto completed her Master’s Degree in Forensic Biology at the University of Calabria – Italy. She is a Certified Specialist in “The forensic Biology Survey” and also a researcher at the Bio Forensics Research Center.

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