Only your hairdresser knows for sure
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Only Your Hairdresser Knows For Sure: PowerPoint PPT Presentation

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Only Your Hairdresser Knows For Sure:. A Lesson on Hair Identification.

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Only Your Hairdresser Knows For Sure:

A Lesson on Hair Identification

Hair recovered at a crime scene can be valuable to forensic scientists. Therefore, crime scene technicians collect any hairs that they find and send them to the lab for analysis. Forensic scientists are familiar with hair structure and chemistry.

  • Hair grows from FOLLICLES or tiny pockets in the skin

  • The entire surface of a mammal is covered with thousands of FOLLICLES

  • Located beside each follicle is a small MUSCLE that can make the hair stand upright.

  • .

  • A NERVE connects the follicle to the brain; that's why it hurts to pull a hair out.

  • A SEBACEOUS gland in the wall of the follicle produces SEBUM, an oil that is essential for normal hair and skin.

  • The entire length of the hair includes the ROOT, which is embedded in the skin follicle and extends the length of the SHAFT to the hair TIP


  • A hair is composed of three distinct layers: CUTICLE, CORTEX, and MEDULLA

    • CUTICLE: a hard OUTSIDE COVERING that protects the inner layers of the hair made of overlapping SCALES that point toward the tip.


  • There are many types of arrangements of cuticle scales, varying from LOOSE, OPEN scales to

  • TIGHT, FIRM scales.




    • 75-90% of a human hair is composed of CORTEX

    • These cells contain the PIGMENTS that give hair its COLOR

    • Forensic scientists sometimes use COLOR, SHAPE, and DISTRIBUTIONOF PIGMENT granules to tell the difference between hairs of two individuals


    • The medulla of a hair is made of cells that run through the center of the cortex like a CANAL

    • In humans, this is a very SMALL layer.

    • The medulla may not be a continuous canal. It can be CONTINUOUS, INTERRUPTED or FRAGMENTED




    Forensic scientists determine the MEDULLARY INDEX of a hair by determining the diameter of the MEDULLA relative to diameter of the HAIR (expressed as a fraction)

    • Humans have a medullary index of less than 1/3

    • The medullary index of animals is 1/2 or greater.

    • The SHAPE or PATTERN of a hair’s MEDULLA help scientists determine its source.

    • In many animals, the MEDULLA makes up most of the CORTEX The arrangements vary:

    • Cats: “string of pearls”

    • Deer: spherical cells that occupy the entire cortex

    • Dog: discontinuous medulla

    • Rabbits and Mice: Large, fragmented medullas






    Hair Identification

    • When humans DYE their hair, it can help identify SINGLEstrands.

    • Dye can be present in either the CORTEXor the CUTICLE.

    • Bleaching removes the color from the hair and gives it a YELLOW tint.

    • The length of naturally colored “roots” beneath a tinting job is a way of identifying the owner of a hair.

    • Hair grows at the rate of 1.25 cmper month

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