Trace Evidence: Hair

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Trace Evidence: Hair

by Kathy Steck- Flynn

Edmond Locard was the founder of the Institute of Criminalistics at the University of Lyon in France. Locard believed that that when on person came in contact with another person or object a cross transfer of minute particles occurred. This theory became known as the "Locard Exchange Principle". Locard believed that crimes could be solved by inspecting the "dust particles" carried to and from a scene. This science is known today as criminalistics and has led to the rise of the forensics laboratory (from Mount Royal College background notes FORE 4407 section 3: Unit 4) Francois Goron, head of the French Surete, seems to be one of the first modern investigators who tried to use hair to identify a killer. In his first case hairs found clutched in a dead woman's hand could not be identified as human simply because there was no information on the subject.

The inability of the scientific community to distinguish between animal and human hair raised interest in the analysis of hair. In the years that followed researchers began to collect information about the structure of human and animal hair (Block, 1979). In 1899, several years after his original failure, in a case known as "L'affaire Gouffe" Francois Goron was able to establish that a murder victim's hair had been dyed. Establishing this simple fact led to the identification of Gouffe's body and subsequently to the arrest of his killers (Block 1979). Francios Goron had successfully used forensic hair examination to solve a crime.

The success of this case and others has led to extensive research into the nature of hair and how it can be used in forensic investigations. In this article I will attempt to cover some of the basic information regarding the collection and use of hair as forensic evidence. Hair must never be used as the sole indicator of guilt. Visual comparison alone is subjective and open to interpretation of the individual scientists. However, when hair is used in conjunction with D.N.A. and other evidence it can be a powerful tool for an investigator.

Hair is in all likelihood one of the most common types of trace evidence (Nickell, J. & Fischer, J. 1999). Hair is extremely variable among both individuals and racial populations (Crocker 1999) (Saferstein, 2004) (Greenshields & Scheurman, 2001). Great care must be used in the use of hair as evidence. Hair may in some cases rule out certain populations or help identify an unknown victim (Block, 1979). Cross transfer of hair from a victim to a suspect or vice versa may substantially raise the probability that the victim and perpetrator were in contact (Cocker, 1999). However, it can never be used as the so called "smoking gun" which would prove a person's guilt. As with most forensic evidence the information obtained from hair is expressed in terms of probabilities of a match rather than an absolute match (Crocker, 1999).

Collection of Evidence

Methods of collecting hair evidence vary according to the scope and the circumstances of the investigation (Greenshields & Scheurman, 2001). In some circumstances more than one method of collection will be utilized. In general the methods of collection hair as potential evidence have not changed since the last quarter of the 19th century (Bisbing, 2001).

There are six main methods of collection. The first is collection of visually observed hairs. The investigator may collect visual observable hairs by hand or with tweezers. The use of tweezers is not recommended in most cases because they can cause damage to the structure of the hair. Tweezers can also crush the delicate root structure and surrounding tissue which is used in D.N.A. analysis (Greenshields & Scheurman, 2001) (Bisbing, 2001) Forensic light sources such as infrared or laser may be used to enhance the ability of the investigator to visually identify hairs (Greenshields & Scheurman, 2001) (Crocker, 1999) Clear tape can be used to lift both visible and non-visible hair from a variety of surfaces. In Canada this is the most widely used method (Crocker, 1999) Clear tape can be used in either a roller type form or as sheets. When sheets or squares are used on a garment each section will be labeled as to which part of the garment the samples were obtained from (Bisbing , 2001) It is important that the tape is not so sticky that it becomes clogged with fibres from then garment or material it is used on (Crocker, 1999).

Vacuuming method of collection used for large crime scenes or where the most likely points of transfer or unknown. Vacuuming can also be used on stationary objects which cannot be transported (Greensheilds & Scheurman, 2001). The vacuums used by investigators are fitted with a special filter which can be removed and labeled appropriately. (Crocker, 1999)

Another method of collection is brushing, scraping or shaking of garment or other cloth objects. The material being examined is held over a white sheet of paper and abraded in order to dislodge and hair adhering to it (Bisbing, 2001) Trace evidence found on the white paper is then separated into classes such as hair, fibre, glass etc. and analyzed accordingly. This method is the second most commonly used method in Canada for the collection of trace evidence. (Crocker, 1999)

Some garments and other fabrics may be placed in a bag and agitated. This method allows the investigator to collect the evidence at the bottom of the bag rather than have it disperse into the air (Bisbing, 2001).

Finally, when collecting hair evidence combing and clipping are methods used. When looking for cross transference of hair (usually pubic) from a suspect to a victim or vice versa combing is used to extract loose hairs (Greenshields & Scheurman, 2001)( Bisbing, 2001) (Saferstein, 2004) Anyone who may have left hair at a crime scene should be sampled for comparison purposes. Approximately 100 scalp hairs from various areas of the head should be pulled and combed. Pubic and other body hair can be pulled, clipped and combed. Approximately 30-50 hairs should be collected and labeled as to the body area of origin and the method of collection (Greensheilds & Scheurman, 2001) (Bisbing, 2001) (Saferstein, 2004).

Structure of hair

A hair sample is analyzed as a whole and in cross section.

When viewed as a whole a hair consists of three parts. These three parts are the root, the shaft and the tip. The length and the shape of a hair can be used to identify the place on the body from which it originated (Innes, 2000) Sites of origin are considered to be the scalp, eyebrow , beard, underarm, body and pubic region (Lane, 1992) Some researchers also include ear hair as a separate region of origin (Crocker,1999)

As a whole a hair is made up of a root (bulb), shaft and tip. Investigators use the shape of the root to indicate the stage of growth and whether the hair was pulled out or shed naturally. The root may also contain follicular tissue which is used for D.N.A. testing.

The shaft can be examined, using a compound microscope and backlighting, for unique characteristics within the shaft. Characteristics include the shape and type of the medulla, the presence and dispersal patterns of pigment granules and the shape and pattern of the external scales. The overall condition of the shaft can show damage such as insect bite marks indicating a hair not recently shed. Burning or crushing will cause the shaft to curl and bubble ( Chayco & Patreco, 2003). Hair grows at a fairly constant rate of 1 mm per day (Crocker, 1999). With this knowledge an investigator can estimate the time since a dye, permanent wave or other exposure to chemicals occurred (Crocker, 1999).

The tip of a hair may reveal chemical or heat treatment indicating head hair. It may also be blunt ended indicating beard hair that has been shaved or clipped.

A hair in cross section can be visualized as being like a pencil. The medulla is the lead. The cortex is the wood. The cuticle is the paint covering the wood (Bisbing, 2002) The medulla may be viewed microscopically by dry mounting the entire hair or by embedding the hair in paraffin wax and slicing it into thin sections. The medullary index is used to distinguish animal hair from human hair. It is expressed as a ratio of the shaft diameter to the diameter of the medulla (Saferstein, 2004). In animals the medulla will make up more than 1/2 of the total diameter of the hair. In humans the ratio is usually less than 1/3 (Saferstein, 2004) The medulla can be classified as appearing either absent, fragmented, interrupted or continuous (Lane, 1992) (Saferstein, 2004). Most human head hair with the exception of that of the Mongoloid race has no medulla or a fragmented one. People of the Mongoloid race have a continuous medulla.

Most animals have a continuous or interrupted medulla. Hair of animal origin may exhibit specific patterns such as a uni or multiserial ladder (rabbits) or a lattice (Deer) (Saferstein, 2004)( Lane, )1992 The shape of the medulla as well as the pattern is exhibits can be used to determine species, and when human, racial origin (Saferstein, 2004) (Lane, 1992).

The cortex surrounds the medulla as does the wood of a pencil around the lead. Microscopic structures within the cortex such as pigment granules and fusi (air bubbles) are used to compare one hair to another (Saferstein, 2004) (Kubic & Patraco, 2003).

The cuticle is like the outer paint of the pencil. The cuticle is used mainly to observe the scale patterns present which indicate species (Saferstein, 2004) (Lane, 1992) (Crocker, 1999) (Kubic & Petraco, 2003) .

Scale patterns are observed by embedding the hair in a liquid medium often clear nail polish and allowing it to set. Once the polish has air dried the hair is removed leaving a cast of the outer scales (Crocker, 1999).

Scale structure is used to determine species. The patterns may be coronal, petal, or umbricate. Umbricate scales are overlapping and exhibit no apparent pattern. Umbricate scales are found in humans (Saferstein, 2004) Petal scales resemble the scale of a reptile and are not found in humans. Coronal scales are symmetrical and overlap one and other. They are not usually found in humans (Cheyko & Petreco, 2003).

The Root

The root of a hair is were lies the almighty D.N.A.. It can also tell an investigator whether the hair in question has been pulled out or shed naturally.

There are three stages of hair growth. The first stage is the Anagen stage in which the hair is actively growing. If a hair is pulled out during this stage the root bulb will appear flame shaped (Saferstein, 2004). Hairs forcibly removed during this stage of grow will have follicular tissue (clear tissue just above root bulb) adhering to it. This is the richest source of D.N.A.. D.N.A. from an Anagen hair can provide nuclear D.N.A.. Nuclear D.N.A. can be analyzed to create a profile of the donor unique to that individual. D.N.A. profiles can help match a suspect or victim hair sample to known samples. The Anagen stage of growth lasts for up to six years (Saferstein, 2004).

The second stage of growth is the Catagen stage. In this stage the root becomes elongated. This is the end stage of growth. The root pulls back and can easily be dislodged (Saferstien, 2004). The Catagen stage lasts for several weeks.

The final stage is the Telagen phase which can last up to 6 months. In this stage the root is club shaped and the hair is naturally shed. (Saferstein, 2004) (Crocker, 1999) (Kubric & Petrico , 2003)


One of the most common applications of hair analysis is to determine whether the hair in question is human or animal in origin. This is done by comparing the scale patterns of the cuticle and the medullary index. The medullary index is the ratio of medulla to shaft size. In humans the ratio is usually under 1/3 (James & Norby, 2003) (Saferstein, 2004) The shape and the pattern of the medulla also indicate whether a hair is human or animal. These same observations will tell an investigator what species of animal the hair came from.

The shape of the root can be used to identify the stage of growth and whether the hair was pulled or shed (Innes, 2000) (Crocker, 1999) (Saferstein, 2004) Lack of a root could indicate that the hair has been cut. Damage to the hair such as crushing, burning and other chemical treatments can be observed from the shaft of the hair. Given an average growth rate of 1mm per day the investigator can estimate the length of time that has elapsed since the damage occurred. (Crocker, 1999)

Racial origin can be guessed at but in a country such as Canada where many people are of mixed descent this can be difficult. If the hair has a follicular tag (it was pulled out) D.N.A. analysis may be possible. From this the sex and genetic profile can be determined. If no follicular tag is present Mitochondrial D.N.A. analysis is possible. Mitochondrial D.N.A. analysis creates a profile of the genetic material from the person's mother only. Mitochondrial D.N.A. cannot be used to distinguish between siblings.

In a study conducted by the F.B.I. 11% of hairs deemed to be matches upon visual inspection where subsequently found to be non matches after D.N.A. testing. (Saferstein, 2004)

There are situations in which hair is not particularly useful as evidence. In domestic disputes, murders and other crimes in which the victim and the suspect live together or have lived together hair is of little use.

Other Considerations

One of the final uses of hair is its use in toxicology. Hair remains after the flesh has disintegrated. Unless it is burn or treated with acid or alkali hair with remain as evidence long after most other evidence has disappeared.

One of the most famous cases of poisoning may have been solved by modern technology and hair. Napoleon Bonaparte was the emperor of France. He waged war on most of Europe during his reign. In the end he was captured and exile to a small island in 1821. Napoleon Bonaparte was and is famous for the paintings done of him showing him with his hand inserted into his shirt covering his stomach. This habit of putting his hand over his stomach led to the belief that he may have had stomach cancer. His father had died of stomach cancer many years before. (Owen, 2000) (Innes, 2000).

Before he died he wrote that he believed he was being poisoned by his English captors. When he died his valet kept a lock of his hair. The lock of hair survived and with the advent of new technology was tested using neutron activation analysis. The results showed that the emperor had been subjected to heavy dosed of arsenic. The doses had been administered over a period of four months (Innes, 2000). It is impossible to say who poisoned Napoleon Bonaparte but it is now known he was poisoned.


Hair can provide a myriad of information. None of this information can be used as solid evidence on its own. Hair is best used to back up other forms of evidence. As I have said earlier it is all a matter of probabilities. The chances of a single hair from a victim being found on a suspect might be 1/800 that it got there accidentally. If, however, hair from the suspect is also found on the victim the probability of an accidental transfer increases to 1/640,000. Hair should be used as a support to other evidence.


  1. Block, Eugene. Science vs Crime: The Evolution of the Police Lab. (1979). Cragmont Publications. San Fransisco, California.

  2. Bisbing, Richard E., (2001) Finding Trace Evidence. in Mute Witnesses: Trace Evidence Analysis. Houck, Max., (ed.) Academic Press, San Diego, California

  3. Crocker, James E., (1999) Trace Evidence. in Forensic Evidence in Canada(2nd ed.) Chayko, G. M. & Gulliver E. D. (eds.) Canadian Law Books Inc., Aurora, ON.

  4. Fernelli, Roxana,. (2002) Silent Witness: How Forensic Anthropology is used to solve the world's toughest crimes. Firefly books Inc., U.S.A.

  5. Greenshields, Malcolm, R. & Scheurman, Gordon D., (2001) The Crime Scene: Criminalistics, Science and Common Sense. Pearson Education Canada Inc.,Toronto.

  6. Innes, Brian., (2000) Bodies of Evidence. Amber Books. London, England.

  7. Kubic, Thomas A. & Petraco Nicholas.(2003) Microanalysis and Examination of Trace Evidence in Forensic Science: An Introduction Scientific Investigative Techniques. J.H. Stuart & J. Nordby (eds). CRC Press LLC, Boca Raton , Florida

  8. Lane, Brian. (1992) The Encyclopedia of Forensic Science. Headline Book Publishing Inc., London, England.

  9. Nickell, J. & Fischer John F., (1999) Crime Science: Methods of Forensic Detection. University of Kentucky Press. Lexington, Kentucky.

  10. Owen, David (2000) Hidden Evidence: Forty True Crimes and how Forensic science solved them. Firefly Books Inc., Buffalo, N.Y.

  11. Saferstein, Richard. (2004) Criminalistics: An Introduction to Forensic Science. (8th ed.) Pearson Education Inc., Upper Saddle River, New Jersey

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