Hair & Hair Identification Forensic Science 2

Hair There are millions of hairs scattered across the body Hair is all over the body expect on palms of hands, soles of feet, nipples and lips Hair is the fastest growing tissue in the body It’s main role is to provide minor protection Guards the head against bumps and heat loss Eyelashes shield the eye Nasal hairs trap foreign particles

Structure of Hair Hair is all most entirely dead epidermis and proteins The central core is the medulla, which is surrounded by a bulky cortex, which is further covered by a cuticle The cuticle is formed by a single layer of cells that overlap one another like shingles on a roof

Structure of Hair The cuticle is the most heavily keratinized (proteins) part of the hair to provide strength As the hair lengthens the cuticle begins to wear away allowing the inner hair region to “frizz” out – this is known as a split end

Other Structures of Hair Arrector pili are small bands of smooth muscles on each side of the hair root When these muscles contract (as in cold or frightened) the hair is pulled upright This phenomenon can especially be seen in a frightened cat

Hair Variety Hair comes in a variety of sizes and shapes Short and stiff in the eyebrows Long and flexible on the head Nearly transparent in some areas Hair pigment is made by melanocytes in the hair bulb Varying types and amounts of melanin account for all types of hair colors from pale blond to pitch black

Hair Variety When the hair is perfectly round, the hair tends to straight and coarse When the hair shaft is oval hair is smooth and silky and the person has wavy hair When the hair shaft is flat and ribbon-like, the hair is curly or kinky The physical appearance of hair can be affected by nutritional status and intentional alteration (heat curling, perms, straightening, etc.).

Hair Identification Basics Characteristics of the cuticle is important in distinguishing between hairs of different species but is often not useful in distinguishing between different people. Distribution of the cortex is perhaps the most important component in determining from which individual a human hair may have come.

Hair Identification Basics In order to test hair evidence for DNA, the root must be present. Hairs that are forcibly removed are most likely to contain DNA

Hair Identification The first step is to determine whether the hair in question originated from an animal or a human being. If the hair originated from an animal, it is possible to further identify it to a particular type of animal. If it originated from a human, the next step is to determine what region of the body it came from

Hair Identification The hair in question is then analyzed to determine if it was naturally shed or forcibly removed Hair forcibly removed from the scalp will exhibit stretching and damage to the root area. Naturally shed hairs, such as a head hair dislodged through combing, display undamaged, club-shaped roots. Forcibly removed hairs may have tissue attached.

Other Identifying Elements Hair can also be analyzed for race determination Asian Are regularly coarse, straight, and circular in cross section, with a wider diameter than the hairs of the other racial groups. The outer layer of the hair, the cuticle, is usually significantly thicker than the cuticle of African and Caucasian hairs. Asian hair can have a characteristic reddish appearance as a product of its pigment. Caucasian Can be of fine to medium coarseness, are generally straight or wavy in appearance, and exhibit colors ranging from blonde to brown to black. The hair shafts of Caucasian hairs vary from round to oval.

Other Identifying Elements African Are regularly curly or kinky, have a flattened cross section, and can appear curly, wavy, or coiled. The density of the pigment in the hair shaft may be so great as to make the hair opaque. A African hair shaft exhibits variation or apparent variation in diameter because of its flattened nature and the manner in which it lies on the microscope slide.

Other Identifying Elements A hair that has been chemically combined can also be determined Hairs that have been obtained by a decomposing body can be determined