Microscopic Hair Analysis: Procedure & Results

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  • 0:03 Opening Example Scenario
  • 0:36 Microscopic Hair Analysis
  • 3:04 What Hair Samples Really Mean
  • 3:53 DNA Analysis
  • 5:25 Lesson Summary
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Lesson Transcript
Instructor: Patricia Jankowski

Patricia has a BSChE. She's an experienced registered nurse who has worked in various acute care areas as well as in legal nurse consulting.

Microscopic hair analysis is a forensic technique that can be used to help identify a suspect in a crime. This lesson is about microscopic hair analysis, procedures used, and their results.

Opening Example Scenario

''Hey, Detective Mulligan, did you check out that apartment yet where the Tuesday night homicide happened?''

''Yeah, Officer Clancy. It's still taped off. We did a pretty thorough check of it. Why?''

''Because we have a kid who was on his bike that night who says he saw somebody exit the building in a hurry, and a comb fell out of his pocket as he ran away. And guess what? The kid has the comb.''

''Well, Clancy, we're on our way to interview the prime suspect. I'll ask him for a hair sample. Today may be our lucky day!''

Microscopic Hair Analysis

Investigators find unknown fibers and hairs at crime scenes frequently, and this valuable evidence can be analyzed in a number of ways to help determine whether a suspect is innocent or guilty, in what is known as microscopic hair analysis. Microscopic hair analysis by itself isn't an exact, irrefutable science that produces airtight evidence. However, it is an artful technique that, when used by an experienced forensic scientist, can be very useful as a starting point for solving a crime, in determining the cause of death, or simply for identifying someone. The study of human hair is also known as trichology.

Hair Anatomy

Before discussing microscopic hair analysis, it's important to understand the anatomy of a human hair. In humans, hair is embedded in the outer layer of skin. The most deeply buried part of the hair is the follicle, or bulb, which is where cells originate to build the shaft. The shaft of a hair is the part that extends outward.

Hair itself is composed mainly of a protein called keratin. A hair shaft has three layers, which are the outermost cuticle, the cortex which comes next, and the inner medulla.

The cuticle is made up of overlapping scales that cover the outside of the hair shaft. The cortex of a human hair is the largest layer and contains granules of pigment that create the hair color. The medulla is a column of cells that runs lengthwise through the center of the cortex.

Stages of Hair Growth

Let's take a look at stages of hair growth:

The stage of growth of a human hair is also a relevant factor in a forensic investigation. There are three stages, which are:

  • Anagen - This is the growth phase during which new cells actually grow in the hair follicle. This phase can last as long as six years.

  • Catagen - In this phase, the follicle slows down cell production and prepares for the resting phase. This phase lasts about two to three weeks.

  • Telogen - This is the resting phase. In this phase, cell production stops and the hair falls out. This phase lasts about two to six months.

All three of these phases occur simultaneously and at any given time, most hairs (80 to 90 percent) are in the anagen phase, while 10 to 18 percent are in the telogen phase, and approximately two percent are in the catagen phase.

Why are these facts important to a forensic investigation of hair? Let's talk about that next...

What Hair Samples Really Mean

The microscopic appearance of the various components of the hair shaft can give a lot of information about who it came from. The cuticle of the shaft cannot identify a specific individual, but it can identify what species the hair comes from. The pattern of scaling can be seen by casting the hair in nail polish. When it hardens, there's a picture of the scaling pattern, which can then be examined under a microscope.

The cortex can also be seen under a microscope to compare the appearance of the pigment granules. If the hair shaft is from a suspect, these granules can tell the investigator the color of the hair.

The medulla of the hair shaft varies in appearance in humans by race. People of Asian descent have a continuous medulla, while people of other races might have an intermittent medulla or none at all.

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