22 Identification through Hair

Learning Objectives:

Through this text, one will be able to know about the morphological and structural characteristics of hair with their types and formation. Further, how hair strand/strands can be useful in identification or at the scene of crime with the help of morphological characteristics of the hair samples such as medullation, diameter, form and cross-section to determine age, sex, ABO blood groups, body area and race.

Content: The text consists of following sub-headings including:

• Introduction of Hair
• Structure of Hair
• Hair Formation and Growth
• Types of Hair
• Role of Hair in Identification
• Medico-Legal Importance of Hair

Identification through Hair

1. Introduction

Human hair has a significant potential in forensic anthropology and has been extensively used in forensic investigations. Investigators believe that their presence can associate a suspect to a victim or a suspect/victim to a crime scene primarily because hairs can be transferred from the suspect to the victim and/or vice-versa during physical contact. The types of hair recovered, the condition and number of hairs found in the scene of crime all have great relevance as evidences in criminal investigations. The forensic anthropologist routinely compares the morphological characteristics of the hair samples in question to known hair samples to determine a transfer. Human hair has also been successfully used to assess drug and substance abuse as drugs of abuse cannot be often detected in body fluids. Using very sophisticated analytical techniques such as immunoassay and gas chromatography, investigators are now extensively using human hair to solve cases of poisoning and drug and substance abuse. Hairs may be defined as slender filamentous outgrowths of the skin and are primarily composed of keratin. It differs from one animal species to another in the basis of length, colour, shape, root appearance and morphological characteristics. There is also a considerable deal of variability in the types of hairs that are found on the body of a particular animal. In humans, hairs are distributed on the head, pubic region, arms, legs, and other body areas.

Structure of Hair: Hair is a biological polymer with over ninety percent of its dry weight being made up of keratin protein. Keratins are cystine-containing proteins, which forms two large groups called Intermediate filament proteins and Intermediate filament associated proteins (Powell et al. 1998) that are almost equally abundant in most hairs. Of the several types of bonds that stabilize the keratin molecule, the most unique is –S-S-. This –S-S linkage is formed by two cystine residues contained in adjacent polypeptide chains and it is this disulfide bond that is mainly responsible for keratin’s resistance to destruction. The human hair follicle is a structure, which is formed as a result of epithelio-mesenchymal interactions initiated around the third month of fetal development. It is very complex, consisting of more than twenty different cell types distributed into six main areas. T hese areas are the connective tissue sheath, the dermal papilla, the outer root sheath, the inner root sheath, the shaft and the sebaceous gland. This complex appendage behaves in a unique pattern in mammals as, after a hair production phase, it involutes in situ before entering a resting phase after which it renews in a cyclical but stochastic fashion. The hair follicle thus is a fully autonomous skin appendage with its own hormonal control, its own autocrine and paracrine network and its own cycle, appearing as an incredibly complex and stable structure that summarizes the main rules of tissue homeostasis (Bernard 2005). Hair consists three zones: cuticle, cortex and medulla.

Cuticle: This is the outer zone and consists of non-pigmented scales of keratin and forms a certain pattern. Cortex: This is the middle zone consisting of longitudinally arranged, elongated cells without nuclei, and varying amount of pigment, which gives hair its colour. Medulla: This is the inner zone. It is known as the medullary canal or the central shaft. It contains considerable amount of pigment in animals not in humans. Medullary index is also important and used to see the difference between animal and human hair. Medullary index is the ration of the diameter of the medulla to the diameter of the shaft. In human hair, only the cortex is pigmented; the medulla is narrow, absent or fragmented. The root has the appearance similar to that of shaft except that it is enlarged in the form of bulb or knob.  The tip of the  hair  is tapering  and generally tapering and  non-medullated (Parikh,  1970).

2.   Hair Formation and Growth

Hair formation begins in the third month of fetal life. Each hair grows through a follicle and is made up of epidermal cells that grow under the dermis. Initially the epidermis thickens and cells begin to grow down into the dermis. This down growth forms a cap over some of the connective tissue to create papillae whose cells multiply to form the hair. As these cells are pushed up the central canal of the hair shaft and away from their source of nourishment, they become impregnated with keratin. The morphogenesis of most hairs follow a cyclic pattern of cell proliferation and differentiation initiated in mid to late embryonic development and repeated throughout life (Orwin 1979).

3.   Types of Hair

Humans have several different types of hair that can be classified depending on their body position and form. Generally three different hair types are found. They are based on the length and diameter of the hair follicles in the skin and called lanugo, vellus and terminal. Lanugo is the hair type produced in the very first cycle of hair growth when a hair follicle enters shortly after it develops in the embryo. These hairs are fine and soft, and they grow all over the baby’s body and its main function is to retain body heat. They all grow at the same rate and so are of the same length. Around the eighth month of development this hair is usually shed and often a second generation of lanugo hairs then starts growing and lasts until the first three or four months of extra uterine life are completed. These are then replaced by vellus hair. Vellus hair is short, fine, “peach fuzz” unpigmented hair. It is very soft, much softer than lanugo and grows in most places on the human body in both sexes. It is usually less than two centimetres long and the follicles are not connected to sebaceous glands. Vellus hair is also present among pre-adolescents. Terminal hair is developed hair, which is generally longer, coarser, thicker, and darker than vellus hair. The phases of growth in terminal hair are more apparent than in vellus hair and the former generally has a longer anagen phase. Terminal hair contains a large hair follicle and sometimes, a medulla. During puberty many hair follicles in the pubic region, armpits, legs, chest and face, the latter two in case of males, transform from vellus hair to terminal hair under the influence of hormones. Terminal hairs can be further subdivided into different types depending on their nature and/or position of growth on the body. The different types of terminal hair types include hair of the eyebrows, eyelashes, head hair, beard hair and pubic hair.

4.   Role of Hair in Identification

The forensic anthropologist compares the various morphological characteristics of the hair samples such as medullation, diameter, form and cross-section. The identification can be done as follows:

Body Area Determination: The body area from which a hair originated can be determined by general morphology. Length, shape, size, colour, stiffness, medullar appearance, curliness, and microscopic appearance all contribute to the determination of body area. There is a wide range of interpersonal variation in head and pubic hairs as a result of which, the majority of work in forensic anthropology has been in comparing and differentiating hairs from the head and pubic regions. Head hairs can appear uncut, with tapered tips but are more often cut with scissors and razors. In general these hairs are subject to more alteration than hairs from other body areas. Alterations can be attributed to the use of chemicals (hair dyes, rinses, permanents and frosts) and also to the environment (exposure to excessive sunlight, wind and dryness). The known sample usually contain a random sampling of hair from different areas of the scalp. Pubic hairs commonly may possess tapered tip, but they also be cut with scissors and razors. Presence of facial hairs, more commonly called beard hairs or moustache hairs, on the clothing of a suspect or victim may help establish contact between these individuals.

Racial Determination: Forensic anthropologists routinely try to establish the racial affinities of the head hair samples. The main features of hair that are studied are shape of the longitudinal cross section, hair pigmentation, shape of the cuticle, hair texture, medullation and hair form. In case of Caucasoid, the cross section varies from round to oval, with an evenly distributed pigment granules, a colour ranging from blonde to brown to black, medium cuticle, fine to medium coarseness, discontinuous medulla and a wavy hair form. The Negroids exhibit a flat cross section, a dense pigment, a thin cuticle, an absence of medulla and a curly/ woolly/kinky hair form. Negroid hair pigment granules are larger than those found in other racial groups and the shaft exhibits variation or apparent variation in diameter as it is often flattened nature and the manner in which it lies on the microscope slide. Twisting of the hair shaft (buckling) may be present, and the hair shaft may be frequently split along its length. The hairs of Mongoloids show a round cross section and a straight hair form, having a characteristic reddish appearance or tinge. These hairs are often coarse having a wider diameter than those of the other racial groups. The cuticle is usually thicker than that of Negroid and Caucasian hairs, and the medulla is continuous. The hair shaft or cortex of Mongoloid hair contains pigment granules that are generally larger in size than the pigment granules of Caucasian hairs.

Sex Determination: Sexing of a human hair is difficult, except that of beard and moustache hair. In human hair Barr- bodies are found in hair follicles in a proportion of 29+5 percent in the female and 6+2 percent in male. The characteristics and distribution of hair help in determining sex. Male hair is usually thicker, coarser and darker than female. Female scalp hairs are generally fine, long and gently taper to end (Parikh, 1970; Modi, 1977).

Age Determination: Age can be determined sometimes from the hair, but only within wide limits, as between that of an infant or an adult. Roots of hair from children will dissolve rapidly in a solution of caustic potash, but in older people roots will resist this treatment.

The body hair of the human foetus and the newly born child is fine, soft, non-pigmented (colour-less) and non-medullated. This lanugo hair is replaced by hair which is coarser, pigmented, and medullated and has a more complex scale pattern. At puberty, axillary and pubic hair grows which is at first fine, soft and curly and later becomes coarse, pigmented and spongy. Adult hairs have maximum pigmentation. Loss of scalp hair in men starts from the third decade. In women, there is often loss of axillary hair and an increase of facial hair, at about the menopause. Gray hair usually appears after 30 years (Modi, 1977).

Determination of Hair Treatment and Forceful Removal of Hair: Morphological examination can identify whether a hair sample had undergone artificial treatment such as use of dyes. Moreover, as the growth rate of head hairs is known, the investigator can assess the approximate time of this treatment by measuring the length of untreated area of the hair. This is done by a direct, side-by-side comparison of the colour of the questioned and known artificially treated hairs. A microscopic study of the hair root determines whether the hair was forcibly removed from the body or shed naturally. Hairs that fall out naturally exhibit a club-shaped root, while a forcibly removed hair will be stretched and may have tissue attached to it. The manner in which a hair was removed has considerable forensic value, especially when there is a possibility of violent contact between a suspect and a victim. Microscopic examination can also be used to establish whether the hair was burned, cut or crushed (Sen, 2010).

Determination of Blood Groups through Hair: ABO groups can be determined in a single hair from any part of the boy, by a modified absorption elution technique with 100 percent accuracy. Determination of Hair identical with the Hair of the Victim or the Suspect: By careful comparison one can say that hair could have come from a particular person. Debris, grease etc., adherent to the hair is very important. Microscopically, the intimate structure and shows uniformity in general shade which is not seen in hairs in natural colour. Because of diet and drug intake and atmospheric conditions, traces of 18 elements are deposited in our hair in proportions quite unlike those in other persons, which can be measured through neutron activation analysis. Determination of cause of Injury through Hair: If the hair has not been cut, the tip is pointed and non-medullated, but repeated injury to the tip damages the cuticle due to which the exposed and unprotected cortex splits and frays. The hair of axilla and pubis has frayed ends, so also frequently brushed hair. Blunt injury and crushing with heavy blunt scissors, crushes the shaft with flattening and splitting. A sharp weapon produces a clean, uniform cut surface. After a week the end becomes square, smooth and later rounded but blunt. After 3 to months the end becomes elongated, but the medulla is absent. Hair may get scorched or singed due to burns or firearms injury. Signed hair is swollen, black, fragile, twisted or curled and has peculiar odour; carbon may be found deposited on it. The tip is swollen like a bulb (Modi, 1977).

5.  Medico-Legal Importance of Hair

1)    Hair is important in crime investigation, for it remains identifiable on both the body and the alleged weapons in crimes committed long before. It often provides the only connection between a weapon, or even accused and the victim of an assault. Motor vehicle responsible for injuries may be identified by the detection of hair on the vehicle. In rape and sodomy, the pubic hair of the accused may be found on the victim or vice-versa. Stains on the hair may indicate the nature of the assault, e.g. mud stains in struggle, seminal stains in sexual offences, salivary stains in injury, etc. Stains may be got from the walls, doors, furniture, etc., and may indicate the scene of crime. 2) Hair is important in identification, especially where there has been some known peculiarity of the hair, dyeing, bleaching or artificial weaving. 3) In chronic poisoning with heavy metals, e.g., arsenic, the poison can be detected in the hair. 4) The time of the death can sometimes be determined from the growth of the hair on the face. 5) Singeing of the hair indicates burns or close range firearm injury. 6) It is helpful in differentiating scalds from burns. 7) Age of the person may be determined from growth of the hair on different parts of the body. 8) Sex may be determined from their distribution on body and texture. 9) Nature of the weapon can be made out from the injuries to the hair (Reddy, 2005).

Conclusion: Examination of Hair is one of the important parameter for medico-legal point of view in identification, sexual offenses, and crime when hair or fibre are found, hit and run accidents or chronic poisoning by metals. The point to be considered in the examination of the hairs are- i) the nature, that is, if the material is hair or dome other fibre ii) if it is hair, its source, whether human or animal iii) if human, the race, age, sex, situation, and special features for identification iv) evidence in relation to suspected crime and v) in case of dead bodies, the time since death, if possible.

Summary

Human hair has a significant potential in forensic anthropology and has been extensively used in forensic investigations. Hairs may be defined as slender filamentous outgrowths of the skin and are primarily composed of keratin. It differs from one animal species to another in the basis of length, colour, shape, root appearance and morphological characteristics. There is also a considerable deal of variability in the types of hairs that are found on the body of a particular animal. In humans, hairs are distributed on the head, pubic region, arms, legs, and other body areas. The types of hair recovered, the condition and number of hairs found in the scene of crime all have great relevance as evidences in criminal investigations. The forensic anthropologist routinely compares the morphological characteristics of the hair samples in question to known hair samples to determine a transfer. The forensic anthropologist compares the various morphological characteristics of the hair samples such as medullation, diameter, form and cross-section to determine age, sex, ABO blood groups, body area and race. The point to be considered in the examination of the hairs are- i) the nature, that is, if the material is hair or dome other fibre ii) if it is hair, its source, whether human or animal iii) if human, the race, age, sex, situation, and special features for identification iv) evidence in relation to suspected crime and v) in case of dead bodies, the time since death, if possible. Examination of Hair is one of the important parameter for medico-legal point of view in identification, sexual offenses, and crime when hair or fibre are found, hit and run accidents or chronic poisoning by metals. Human hair has also been successfully used to assess drug and substance abuse as drugs of abuse cannot be often detected in body fluids. Using very refined analytical techniques such as immunoassay and gas chromatography, investigators are now extensively using human hair to solve cases of poisoning and drug and substance abuse.