Hair is a tough protein filament that grows form follicles which are present in the junction between the deep layers of the dermis and the hypodermis. Protein from which hairs are made of named as alpha keratin. In hair follicles, living cell divide and grows to hair shaft. Hair is made up of 95% keratin which is synthesized by keratinocytes and is insoluble in water, it ensures impermeability and protection for the hair strands.
Hair is a type of trace evidence which easily found on crime scene, and it helps in establishment of link between suspects which are supposed to have link with crime and victim. The average hair sample submitted as evidence ranges from 24 to 50 strands. Hair sample is always considered as associate evidence.
Types of Human Hair:
◾ Lanugo– Soft hairs which grows all over the body. Fetuses have lanugo hairs at the end of pregnancy, and they lose their hairs within a 1-2 week.
◾ Vellus– Short, light-colored hairs which develops during childhood and barely noticeable. Have no sebaceous gland.
◾ Terminal– Thick, pigmented androgenic hair present on the scalp, face, armpits and pubic area.
A.) Hair Shaft- that part of hair which is above the scalp and made of toughened protein called keratin. These pigments are held together by two kinds of bonds- hydrogen bonds and disulphide bonds. It made up of three layers- cuticle, cortex, and medulla.
Hair consists of two different parts:
Cuticle- is the translucent outermost protective layer of hair which is made of dead cells called as keratin. It has cells shaped like scales of different types from root end to tip end of hair.
Pattern of scales present in cuticle are:
✔ Coronal– hair which have crown shaped scales. Mainly found in dogs, bats, rodents etc.
✔ Spinous– hair which have petal like scales, found in cat
✔ Imbricate– hair which have flattened scales, mainly found in humans.
Cortex- present between cuticle and medulla. It consists of pigment known as melanin which gives natural color to hair strands. It also contains long keratin chains that add elasticity, suppleness and resistance to the hair.
The amount of a pigment called melanin in hair determines hair colour. People with black or brown hair have an abundance of one type of melanin called eumelanin. People with red hair have an abundance of another pigment called pheomelanin.
Eumelanin gives brown or black color to hair strands and pheomelanin gives red color to hair strands. Color distribution in human hair strands is towards cuticle and in animals towards centre.
A condition in which white patches in the hair due to lack or less of melanin is said as Poliosis or Poliosis Circumscripta or White forelock.
Medulla- is innermost layer of cells, and it is only present in thicker hair types. In humans, medulla diameter is less than 1/3rd of overall diameter of hair shaft. Medulla is of five types on basis of appearance- continuous, fragmented, interrupted, solid and absent.
B.) Hair Follicle- it is small and tunnel-shaped structure in epidermis of scalp and from its bottom end hair starts growing. The only ‘living’ portion of hair is found in the follicles. These follicles are known as hair bulbs. The average human has about 100,000 follicles on the scalp alone.
The shape of follicles determines the shape of the cortex and shape of hairs. Hair follicles are attached with sebaceous glands and arrector pili muscle. Three main parts of hair follicles which are found on the head: the infundibulum, the isthmus and the inferior segment which includes the hair bulb.
Infundibulum segment is the upper portion of the follicles which begins at the epidermis surface and extends to the opening of the sebaceous duct. The isthmus is the area between the sebaceous duct opening and the bulge and bulge is the part of follicle which are attached with arrector pili muscle and contains several epidermal stem cells. The inferior segment of the hair follicle extends from the bulge part to the base of the follicle.
Three different growth phase of hair follicles are:
⭕ Anagen Phase- it is a proliferation phase which occurs when the hair follicle is growing a new hair shaft. The only phase during which the inferior segment of the hair follicle is present.
⭕ Catagen Phase- also said as regression phase or transition phase which is the shortest phase. During this phase, cell division ceases and hair follicles begins to regress. Time period is of about two weeks.
⭕ Telogen Phase- it is resting or shedding phase. Follicles remain dormant for 1-4 month.
Hair samples found at crime scene are examined to identify its species, race, place of origin parts of body etc. firstly it is important to collect hair samples very carefully and sent them to forensic laboratories by following proper chain of custody.
Collection of Hair Sample:
🔸️ Collected using forceps carefully and packed into cellophane or paper bag.
🔸️ Samples can be tape lifted using adhesive tapes.
Determination of Species of Origin:
Also Read: General Characteristics of Human Hair
Determination of Origin of Race:
Also Read: Morphological Characteristics of Human Hair for Racial Determination
Determination of Somatic Origin:
It means to identify hair sample belong to which part of species. Somatic origin type may include scalp, eyebrow, face, limb, pubic etc. origin can be identified by considering features such as length, shaft configuration, medullary configuration, cross-sectional shape, texture, tapering and appearance of the root.
Also Read: General Characteristics of Human Hair from Different Sites
Macroscopic Features of Hair:
The Macroscopic Features that can be observed in the hair are:
🔘 Color- White, red, brown, black, and other.
🔘 Hair Pattern- Straight, wavy, curly, kinky.
🔘 Diameter- fine, medium, coarse, variations.
Microscopic Features of Hair:
The Microscopic Features that can be observed in the hair are:
🔘 Color- Natural/treated color of hair.
🔘 Pigmentation- Distribution, Aggregation (density, size), granule (colour, size, shape, destiny)
🔘 Structure- diameter, shape (cross-section, configurations), root shaft[cortex, cuticle, medulla], Tip.
🔘 Hair Follicle- condition of the root area to determine whether the hair was taken forcibly and shed naturally.
Examination Of Hair
Temporary Mount- Mount of the hair strand sample is made on a clean slide using glycerin and covered with a coverslip. The morphological structures of the hair are observed under a microscope and note down hair shaft (cuticle, cortex and medulla) characteristics of the strand.
Scale Casting- A thin coat is painted on a clean slide and the hair to be cast is placed on the slide and allowed to dry. When the surface has dried, the hair is removed to observe the scale pattern.
Polaroid Coater Method- The hair sample strand is placed on a clean slide and the ends of the strand are secured with cellophane tape. A polaroid film coaster is applied 2-3 times along the length of the hair. This coating is allowed to dry for 23-24 hours. The excess coating that protrudes above the flat surface of the cast is sliced and then hair strand is gently peeled by removing cellophane tape. Now, the impressions of the scales can be microscopically observed.
Cross Sectioning- The hair sample is placed in a solution of ether and ethanol in the ratio 1:1. The samples are bundled and dipped in a block of molten wax and is then allowed to cool. Cross-sections can either be taken using a sharp blade or with a microtone to a thickness of 5-10μ. These sections are placed on a clean slide and the wax is dissolved with a drop of xylene. A permanent mount of the sections is prepared and then examined under a microscope.
Age and Sex Determination:
Generally, age cannot be determined by microscopic examination of hair samples, but it helps to differentiate between an infant and an adult individual by examining hair strands.
Sex can be determined from hair follicles which are attached with hair shaft and comes out with hair strand only when hair is pulled out forcibly. Sex determination can be determined through staining of sex chromatin in the nuclei of the cells showing the female indicative of the Barr body (bright spot, top) and male indicative Y body (bright spot, bottom).
Aceto-carmine stain is used for detection of – X bodies in hair, Barr- bodies in hair, Y bodies in hair.
DNA in hair is usually extracted from the root bulb. If a violent crime has taken place as hair could have been forcefully uprooted by both the victim and the perpetrator during a physical struggle. The DNA portion is extracted, amplified and the obtained sequence is run through a criminal database.
Both microscopic and DNA examination helps to narrow down who have been involved in a crime. In cases of mitochondrial DNA examination, it helps to solve the questions are raised related to evolution and inheritance. Hair also provides the information related to the toxic substance or any drug that may have been linked to health or problems in psychological, reproductive disorders and in developmental toxins.