Hair is probably the most frequently used type of trace evidence in forensics today; with modern advances in DNA analysis, the examination and comparison of human hair found at the crime scene is an informative, high-precision forensic technique. Its importance was understood early at the start of forensic science development, with the first examinations held in 1861 by Rudolf Virchow. In the early 1900s, microscopic hair examination was already common in forensics, while s standard of reference, John Glaister’s Hairs of Mammalia from the Medico-legal Aspect, was published in 1931.
In terms of hair composition and physical characteristics, one should note that hair is a thread of natural fiber formed by keratin – a protein with high concentration of cystine-derived sulfur. The hair thread has a cylindrical structure and is formed of inert keratinized cells distributed in accordance with a precise, well-defined design. The typical composition of hair includes 65-95% of proteins, around 30% of water, lipid pigments, and other minor components. However, in chemical terms, over 80% of the human hair is regarded as formed by keratin. Physical properties of hair depend on its geometry and include certain degrees of elasticity, smoothness, volume, shine, and softness. Evaluation of these properties may be done with the help of optical and electron microscopy, mechanical resistance measuring, and optical coherence tomography (OCT) (Velasco et al., 2009).
The value of hair as forensic evidence is explained by the fact that except for burning, it is next to indestructible. Hair contains valuable information about the human subject even if taken from a dead body in an advanced state of decomposition or found on objects long after the moment of crime. Even with simple microscope examination of a single hair, a forensic specialist can tell much about the hair’s owner, such as his/her gender, age, race and ethnicity. Thus, even though hair does not contain unique identifying characteristics of a fingerprint, it is still a highly valuable piece of material for narrowing the circle of suspects by giving associative evidence. In particular, the examination of hair found at the crime scene involves not only its analysis per se, but also analysis of its transfer and persistence, that is, the mode of its loss (whether it was a natural loss, or it was cut, torn from the person’s head, etc.) (Preedy, 2012).
Hair as trace evidence is so valuable because it contains DNA; while a simple microscopic examination can help identify some general characteristics of the suspect, the DNA analysis of hair may give precise individual identification. However, the specimen suitable for DNA testing should have a root, which is mostly present on hair forcibly pulled out during struggle. Moreover, analysis of hair composition can give valuable data on the medications, drugs, and other contaminants that its owner was exposed to recently (Eldridge, 2012).
Overall, it seems that hair analysis has a bright future in forensics mainly due to the fact that it is precise and non-invasive as compared to analysis of other biological specimens. Moreover, it is much more stable in composition that other biological substances, so it is very helpful in detecting substance abuse and personal identification. Therefore, the prospects of hair analysis seem truly optimistic with the increased precision of DNA and chemical testing techniques, and it is recommended to invest more in the advancement of hair testing techniques for the sake of more informative hair analysis for forensic purposes.