Describe the medicolegal importance of hair with its examination.

Structure and Examination

• Structure — a hair consists of a root within the follicle and a shaft above the surface. The shaft has three layers: the cuticle (overlapping scales, whose pattern distinguishes species); the cortex (containing the pigment granules and the great majority of the mass); and the medulla, the central core, whose presence, continuity and width (the medullary index) are of identifying value
• Questions the laboratory is asked, in order — is it hair at all, or a fibre? Is it human or animal? Which region of the body? And can it be attributed to an individual?

Information Obtainable from Hair

• Species — human or animal, and if animal, which; a valuable link in poaching, in hit-and-run involving animals, and in placing a suspect in a particular environment
• Region of the body — scalp hair is long, circular in section, with a tapered or cut tip; pubic hair is short, coarse, wiry and oval in section, with wide medulla and marked buckling — of obvious importance in sexual offences; eyebrow and eyelash hairs are short with a sharp tapering tip and triangular section; beard hair is coarse and triangular; and axillary and body hairs each have characteristic features
• Sex — determined only by demonstrating the sex chromatin or by DNA from the root, not by morphology
• How the hair was separated — a plucked hair has the root sheath and follicular tissue attached and is usually in the growing (anagen) phase; a shed hair has a dry club-shaped telogen root with no sheath; and a cut hair has a flat or angled end with no root at all. This distinguishes hair pulled out in a struggle from hair that has simply fallen
• Whether it is cut, burnt or diseased — burning produces swelling, vacuolation, a bulbous "clubbed" end and a characteristic smell; disease and treatment (dye, bleach, perming) are recognisable, and the length of undyed regrowth dates when the dye was applied
• Poisons and drugs — arsenic, thallium, lead and mercury are deposited in hair as it grows and persist indefinitely, so segmental analysis along the shaft gives a chronological record of exposure over months — distinguishing a single large dose from repeated small ones, which is decisive in chronic poisoning. Drugs of abuse are detected similarly, hair giving a much longer window of detection than blood or urine
• Blood group and DNA from the root

Medicolegal Importance and Applied Aspects

• Sexual offences — the accused's pubic hair on the victim and the victim's on the accused; combings of the pubic region are a routine part of the examination
• Assault and struggle — plucked hairs in the victim's hand, on a weapon or at a scene
• Road traffic accidents — hair adherent to a vehicle, with tissue and blood, linking vehicle to victim
• Poisoning — the chronological record of arsenic or thallium exposure, which no other tissue provides
• Identification — colour, length and treatment as corroborative data, and DNA from the root as conclusive
• Collection — hairs are lifted with clean forceps, air-dried, packed in paper packets, never plastic, and labelled with the exact site; and control samples of 20 to 25 hairs, plucked not cut, are taken from several areas of the relevant region of both victim and accused, since hair varies across the scalp
• Pluck the control samples; cut controls lack roots, cannot give nuclear DNA, and cannot be compared for mode of separation — a routine omission that wastes the whole exercise
• Do not overstate a microscopic hair comparison; the honest opinion is that the hairs are similar and could have come from the same source, or that they are dissimilar, and only DNA converts similarity into identity