Topic: How is hair studied by
a forensic scientist?
Do Now: How often do you get your
hair cut? How do people change the
appearance of their hair?
HW: Textbook pg. 230 #’s 1-5
What is hair?
• Appendage of the skin
• Grows out of organ called the follicle
What are the parts of a hair strand?
• 1. Root/bulb
• Embedded in hair follicle
• 2. Shaft
• Composed of 3 layers
–Cuticle
–Cortex
–Medulla
• 3. Tip
• Where the hair strand ends
Parts of the shaft
• a. Cuticle
– Outside covering of hair
– Made of hardened and flattened scales that overlap (like
shingles on roof)
– Scales always point towards tip of hair
– Useful for species identification
– Can’t be used to individualize one human hair from others
Parts of the shaft
• b. Cortex
– Made from spindle shaped cells
– Arranged in pattern parallel to length of hair
– Filled with pigment granules that give hair color
– When we dye hair, we add pigments to cortex and
cuticle
– When we bleach hair, we remove pigments
How can we tell the natural hair color of a
person by looking at a hair sample?
• Hair grows about 1 cm per month
• You can see difference in color if the
person hasn’t dyed/ bleached their hair for
some time
Parts of the shaft
• c. Medulla (plural is medullae)
– Cells form canal-like structure through hair
– Medulla is very narrow in humans
– More than half the width of animal hair is made up
of the medulla
– Appearance/presence of medulla varies:
• From person to person
• Among different hairs on the same person
• From species to species
Medulla Shape
• Medullae of animals tends to be in a pattern
UNISERIAL (rabbit)
MULTISERIAL (rabbit)
VACUOLATED (dog, fox, common)
LATTICE (deer)
AMORPHOUS (human,common)
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c. Medulla
• 3 types of medulla found in huma hairs
– I.Continuous - most East Asian scalp hairs + pubic hair
– II.Fragmented –
Most human scalp hairs other than
– III.AbsentEast Asian
Continuous Medulla Fragmented Medulla
Absent Medulla
Solid canal
throughout hair
No Medulla Found
Interrupted canals
throughout hair
Parts of a hair strand
• 3. Root/Bulb
– Helps make and grow hair along with
surrounding cells in follicle
– When hair is pulled from root, a follicular tag
may be attached
– We can get DNA from follicular tag
Can we determine where on body
hair originated from?
• Yes!
• Scalp Hairs
– shows little diameter variation
– Pigment is evenly distributed in cortex
• Pubic Hairs
– Wide variation in diameter
– Have continuous medullae
• Facial Hairs
– Are coarse and triangular cross section
shape
• Hair analysis video