Hair Investigation


Edited by Malena González de León

Based on Modern Criminal Investigation by Harry Soderman and John J. O'Connel



W h e r e · t o · f i n d · i t · a n d · w h a t · i t · i n d i c a t e s

This type of evidence can be found in variable crimes, especially in violent homicides. Examples of these are rapes, ravishment, armed crimes, kidnapping, etc. In this type of crimes fighting between victim and delinquent generally takes place, where we can find hair under nails and clothes. Hair can be also find in brushes, beds, floor, carpets, and furniture, and in sexual assaults it must be required that a medical examiner thoroughly look for other's hair in all the people involved.
Hair can come from the scalp, and from different parts of the body, in homicides or assaults where the victim has been hit with something hard it is more probable to find scalp hair, because it will be stuck to the element helped by the blood the it will usually be found here. This type of evidence will determine the object that has been used in the crime.

Hair can give clues of the whether a person has or hasn't been in a specific place or has something to do with a particular object. However, the identification el the hair is not so specific or simple as it is believed Hair can indicate whether a person has or hasn't been at a determine place or if he or she has had something to do with a particular object. However, identification is not so specific nor simple as it is believed, and even though it must always be looked for it at the crime scene, it mustn't be considered as an extremely certain trial evidence piece.



S t r u c t u r e · a n d · C l a s s i f i c a t i on

In human beings, hair can be classified in three big groups:

· Long: more than 15mm: scalp hair, beard hair, chest hair and armpix hair.
· Short: between 12mm and 15mm: eyelashes; eyebrows; nose hairs, and ear hair.
· Villous: between 5mm and 12mm: thin and soft

Each hair is attached to the pilous follicle which is situated several millimeters under the skin surface. Hair it is formed in the bulb cells, where we can also find the pigments which will give the hair's color. Above the follicle the sebaceous glands conducts end.


External Structure

Hair can be divided into root, tube and extreme.
The root doesn't give too much clues about it's origin, and oftenly it is absent. Two type of roots exist: alive and dry, and this classification is extremely important in order to determine whether the hair has been pulled out or if it has naturally fallen.

· If ALL of the hairs have living roots: they have been pulled out
· If ALL have dry roots: the more probable situation is that they have fallen naturaly
· If they are mixed type of roots: they have also been pulled out.

Extremes can be in natural state or can be evidently cut. In wild animals which's hair has never been cut it can be observed the primitive characteristics of extremes, as well as in wemen who's hair has never been cut either.
Appearance varies in the different parts of the body and in different animals. Some have constant thickness and others have thinner extremes. By practicing a transversal cut it can be observed that scalp hair is generally round, although curved hair is oval, while beard hair is triangular with concave sides, etc.

Internal Structure

Under the microscope medulla, bark and cuticle can be differentiated.

Medulla is the most significant as far as investigation is concerned. Hair without medulla can be found, and it is denominated amedullar.
Medulla begins near the root and in old hair, medulla begins pretty upper. In several animals it begins with a cell line which goes along through all the length of the hair till the extreme or it has bifurcations and goes on with several numbers of cell lines ones beside the others.
Medulla can be steady or interrupted. It is steady in a big number of animals and normally it is interrupted in human beings, monkeys and horses.
Medulla diameter can be constant or alternatively biger and smaller, but the useful measure is the one obtained by the difference between the medulla diameter and the hole hair diameter, at it's thicker point, measured with a microscopy with a micrometric glass or graduated ruler. This is called the Medullar Index "I".
According to this index, hair can be divided into three groups:

· Thin medullar Hair: less than 0.5 : human hair and monkeys.
· Médium medullar hair: approximately 0.5: cows, horses and others
· Thick medullar hair: more than 0.5: rest of the animals.

Some human hair show thin and interrupted medulla and commonly it can be found amedular hair, especially in wemen.
This is a table with approximated Medullar Indexes values:

Arm pitch


Cuticle is formed by translucid scales, ones over the others, with the free extreme looking to the hair extreme.

Frequently, at the crime scene, fibers are picked up very similar to hair, for this reason the microscopic examination will clearly determine its origin. Those similar fibers can be: wool, silk, cotton, etc.

Hair is specially examined for its attached dust which gives valuable information about its origin and possible subject's occupation as well as type of crime. For example, a mechanic will have grease and metallic powder and a baker will have flower, etc.

D e f o r m a t i o n s

Hair deformations, especially scalp hair ones can conduct us to very interesting conclusions. If for example a person has been imparted with an axe struck, it will be difficult to find longitudinal deformations, instead it will be cracked near the root. The amount of hits will be possibly reveled by the hair condition, because longitudinal cuts will e seen, signals of several hits.


Cut Deformations: perpendicular or oblique precise cut surface, without scratches will reveal the use of a sharp instrument.

Firearm Bullet Deformations: in this case gunpowder, metallic particles and burns will be found.

Burn Deformations: as a result of flames, lightning, electricity, etc. The scorch produces curling and inflammation with a light grey coloring. All of the burns leave a smell similar to a burnt horn.
Air bubbles similar to a necklace can be sometimes seen in the inside.

Scald Deformations: caused by hot water or vapor. If the temperature is on top the 350° Fahrenheit (175° C), hair will be reddish and will show longitudinal stains caused by the contraction of the medullar cells. Till the 480° F (250° C) hair will curl up and break, reddish color will turn to reddish black, hair turns more transparent and air bubbles conform the typical "necklace".


H a i r · O r i g i n

It is important to have present the fact that none of the before explained properties is an absolute indicator by itself. Here it is a table with the most important differences between human and animal hair.

Human Hair Animal Hair
Air bubbles net Medulla Big and small vacuolar air bubbles net
Invisible cells without water Easily visible cells
I value less than 0.3 I value more 0.5
Medulla without lint Medulla with lint
As a thick handle Bark Thin empty cylinder
Very thin pigment grains Irregular and bigger than human pigment grains
Surpassing thick scales Cuticle No surpassing thin scales, that overlap 4/5 of it's parts.

Human hair identification is extremely difficult, especially if there are not enough hairs to examine. In order to extract some conclusions, hair is measured in its length and medullar index and color compared. Everything must be an estimation. The color will be determined after an "spoken portrait" has been taken.
The medulla examination is important, as well as the root, extreme and pigmentation exam. The results of this tests will be always confirmed with additional tests.