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Hair analysis in forensics – Trichology is the study of hair. It grows at the rate of 0.4 mm/day and nails at 0.1 mm/day. The examination of the it is undertaken to find out:

Is it Hair or is it Some other Fiber?

It consists of bulb or root and a shaft. Considerable force is required to pluck out a lot of healthy growing hair from scalp. An adult can be lifted or dragged by it and the scalp may even be torn from the skull. In most of it, there are three well-defined layers.

  • CUTICLE: This is the outer layer and consists of thin, non-pigmented scales.
  • CORTEX: This is the middle layer and consists of longitudinally arranged, elongated cells without nuclei. Within these cells are fibrils on which theme may be granules of pigment.
  • MEDULLA: This is the inner layer composed of keratinised remains of cells.

FIBERS – COTTON fibers are flattened and twisted tubes. They consist of long tubular cells, with thickened edges and blunt, pointed ends. LINEN fibers show cross lines or folds about which the fiber is often swollen and has a narrow lumen. Fibers are straight and taper to a point. JUTE fibers are smooth without transverse lines. The cell cavity is not uniform. The ends are blunt.

SILK consists of long clear threads without any cells. They are smooth and finely striated. Wool fibers show an outer layer of flattened cells and overlapping margins. The interior are composed of fibrous tissue but sometimes medulla is present.

Human or animal

In hair analysis of color changes along the shaft called “banding” is seen in some animals.

Medullary Index of Hair: It is the ratio of diameter of medulla and diameter of the whole shaft. In humans it is less than 0.3 and in animals more than 0.5 The value varies in the hair of different parts of the body and as such it is also helpful to know the part of the body from which it is derived.


The hair analysis shows that the ones from the head is usually long and soft and taper gradually from the root to the tip. The beard and mustache are usually thicker than the ones of any other part of the body. Eyebrows, eyelashes and nostrils are stiff, thick and taper to a point. The hair on the chest, axillae and pubic region is short, stout and curly. Hair from the axillae and pubic region also show split ends. The ones on the other parts of the body is fine, short, and flexible and does not show pigment cells in the cortex.


Sexing of human hair is difficult, except that of the beard and mustache. Male hair is usually thicker, coarser and darker. In human head hair, Barr bodies are found in follicles in a proportion of 29 ± 5 percent in females and 6 ± 2 percent in males.


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

Age                                       Diameter

Twelve days                        0.024 mm

Six months                          0.036 mm

Fifteen years                       0.053 mm

Adults                                   0.07 mm

The body hair of the human fetus and the newly born child is fine, soft, non-pigmented (colorless) and non-medullated. This lanugo hair is replaced by the one which is coarser, pigmented, 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, and pigmented.

Adult hair analysis shows that it has maximum pigmentation. Loss of scalp hair in men starts from the third decade. In women, there is often loss of axillary and an increase of facial one, at about the menopause. Grey usually appears after forty years.

Has the hair been altered by dyeing, bleaching or disease?

Hair analysis shows that bleached one is brittle, dry, and straw-yellow. If it is colored, the color will not be uniform, the roots are of different color and rough, brittle and lusterless. The scalp will also be colored. The color of head hair will be different from the color of it on other parts of the body. The length of extra-follicular part of an uncolored zone is used to determine the time of the color last applied.

Scalp hair grows at the rate of two to three mm. a week, average being two and half mm; beard has a slightly faster and other ones a slightly slower growth rate. Some can be examined chemically to find out any metal contained in the paint. Dyed hair analysis shows characteristic fluorescence with ultraviolet light. With polarized light microscope, the undyed part appears much brighter than the rest.

Blood Groups

ABO groups can be determined in a single hair if blub is present, from any part of the body by a modified absorption-elation technique or mixed agglutination technique with hundred percent accuracy.


Hair analysis shows that it cannot provide a permanent record for identification, because the distribution and concentration of trace elements along the shaft of a hair varies as it grows. The color of the hair may alter with disease. It is lighter in patients with malnutrition, ulcerative colitis, and Kwashiorkor; the normal color appears when health is restored.

The color of it becomes green from copper, blue from cobalt, and yellow from picric acid poisoning. The hair of copper smelters may be greenish, indigo workers and cobalt miners blue and aniline workers bluish. The color of hair alters sometimes after burial.

Is it identical with that of the victim or the suspect?

By careful comparison, one can say that it could have come from a particular person. Debris, grease, etc., adherent to it is very important.

In hair analysis, it is usually mounted on a glass slide for examination in a comparison microscope. For preparing cross-section, it is embedded in a wax or resin block and sliced finely. The impressions of the cuticle scales are made on cellulose acetate. Microscopically, the intimate structure of the dyed hair appears hazy, and shows uniformity in general shade which is not seen in it of natural color.

Because of diet and drug intake and atmospheric conditions, traces of eighteen elements are deposited in it in proportions quite different from other persons, which can be measured through neutron activation analysis. Recent hair analysis shows that only three out of one lakh persons will have comparable amount of the nine major trace elements.

When it is irradiated in a nuclear reactor, elements are converted to radioactive isotopes. Comparison of the radiation emitted from it with known standards provides quantitative comparison. Electrophorctic and electrofocusing methods to study proteins and enzymes in hair root sheath and matrix proteins are of considerable importance.

Did it fall naturally or was it forcibly removed?

The base must be examined to see whether the root is present. If the hair analysis shows that it has fallen naturally, the root will be distorted and atrophied, and the root sheath absent. If it is forcibly pulled out, the hair bulb will be larger, irregular and the sheath will be ruptured.

What is the cause of the injury?

If it 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, pubis and frequently brushed hair has ragged ends. A blow with blunt objects crushes the shaft with flattening and splitting. A sharp weapon produces a clean uniform cut surface.

Recently cut hair analysis shows a sharply cut edge with a projecting cuticle. After a week, the end becomes square, smooth and later rounded but blunt. After three to four months, the end becomes elongated, but the medulla is absent. It may get singed due to burns or firearm injury. Singed ones is swollen, black, fragile, twisted or curled and has a peculiar odor; carbon may be found deposited on it. The tip is swollen like a bulb.

Medicolegal Importance

(1) Hair analysis is important in crime investigation, for it remains identifiable on the clothes, body and the alleged weapons in crimes committed long before. It often provides the only connection between a weapon or even the accused and the victim of an assault.

  • Motor vehicles responsible for injuries may be identified by the detection of it on the vehicle.
  • In rape and sodomy, the pubic of the accused may be found on the victim or vice versa. In bestiality, animal hair may be found on the body or underclothing of the accused, or his pubic may be found about the genitals of the animal.
  • Hair analysis can also show crime committed. Stains on it may indicate the nature of the assault, e.g., mud stains in struggle, seminal stains in sexual offenses, salivary stains in asphyxial deaths, blood stains in injury, etc. Stains may be got from the walls, doors, furniture, etc., and may indicate the scene of crime.

(2) Nature of weapon can be made out from the injuries to it, and its bulb.

(3) It is useful in identification especially when there has been some known peculiarity of it, dyeing, bleaching or artificial waving.

(4) Age of a person may he determined from the growth of it on different parts of body.

(5) Sex may be determined from their distribution on body, texture and from Barr bodies.

(6) Singeing of it indicates burns or a close range firearm injury.

(7) It is helpful in differentiating scalds from burns.

(8) In chronic poisoning with heavy metals, e.g., arsenic, the poison can be detected in it.

(9) The time of death can sometimes be determined from the hair analysis that is from length of the it on the face.



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