Future of Forensics
Hair Growth Cycle
Hair growth is separated into three phases: anagen, catagen, and telogen. When a strand of hair has gone through all three phases, a new strand of hair grows out. Hair grows about half an inch a month. (Source: Hair Basic Knowledge)
Anagen Phase
During the anagen phase, the hair is steadily growing. It starts growing at the papilla, tissue at the base of the hair. It can remain in this stage of growth for 2 to 6 years; the longer it stays, the longer and faster the hair will grow. While it's developing, cells in the papilla produce more hair fibers and the follicle submerges into the skin to receive nutrients. About 80 to 90% of hair is in this phase. (Sources: FBI Hair Evidence and Hair Basic Knowledge)
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Catagen Phase
Hormones signal the brain to transfer from the anagen phase to the catagen phase. This phase is also known as the transitionaly phase and lasts about 2 weeks. In these 2 weeks, the follicle is rejuvenated but later shrinks to about 1/6 its original size causing the hair shaft to be pushed up. The papilla also begins to disconnect itself from the skin, discontinuing the nutritious blood supply. (Source: Hair Basic Knowledge)
Telogen Phase and Return to Anagen Phase
The telogen phase is also known as the resting phase because it remains resting from anywhere 1 to 4 months. Roughly 10 to 18% of our hair is in this stage. Once the hair is active, the papilla fully separates from the hair follicle, take 5 to 6 weeks. When it's fully separated, the hair falls out and returns to the anagen phase, forming a new strand of hair. (Sources: FBI Hair Evidence and Hair Basic Knowledge)
Hair Analysis
Natural shedding occurs near the telogen phase and generally becomes a major source of evidence. Combing can naturally dislodge hair during the telogen phase because a minor amount of force can easily remove the hair. Hair fallouts caused by natural shedding displays a healthy, undamaged club- shaped root (Figure 1a). Sometimes these hairs can transfer onto another person through physical contact. Hairs from the body can also fall out from excessive
FIGURE 1 Hair Removal a. Natural shedding shows an undamaged club-shaped root. b. Hair removed by pulling would have the appearance of being stretched and a damaged root. c. Excessive force would cause tissue to be removed too.
pulling while still in the anagen or catagen stage (Figure 1b); the growth phase can be determined by carefully analyzing the root. Although gender is challenging to determine through microscopy, females tend to have longer, treated (dyed, permed, bleached, etc.) hair . However, if tissue is attached during the removal, gender can be determined, but is not done often (Figure 1c). It can be done by staining the chromatin found in the detached tissue. (Source: FBI Hair Evidence)
Race Determination
Forensic scientists have noticed the distinctive differences of hair from European descent (Caucasoid), East Asian descent (Mongoloid), and African descent (Negroid). People of mixed descent will show characteristics from two or more racial groups. Hairs from the head is most useful for determining race, but hairs from other body parts are useful as well. (Source: FBI Hair Evidence)
Caucasoid/European Hair
Caucasian or European hair have fine to medium coarseness, are generally straight or slightly wavy, and usually have lighter colors. The cross section also forms a round or oval shape. (Source: FBI Hair Evidence)
Mongoloid/Asian Hair
Mongoloid and Asian hair are generally coarse and straight. They also have a more circular and wider cross section. The cuticle, the outer layer of hair, is usually thicker than Caucasoid and Negroid hair. The granules inside the hair shaft are bigger than Caucasoid hair and are patchily clumped together. (Source: FBI Hair Evidence)
Negroid/African Hair
Negroid and African hair are usually curly and kinky and have a flatter cross section. Negroid hair has larger granules than Caucasoid and Mongoloid hair; unlike Mongoloid hair, Negroid granules are clumped together in various shapes and sizes. (Source: FBI Hair Evidence)
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