Trace Evidence: Hair

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.