DAMAGE, DISEASE, AND TREATMENTS
Humans do many different things to their hair depending on their culture—cutting, dyeing, braiding, even shaving—and this isn’t limited to just the scalp. Some dis eases affect the hairs or the follicles and are distinctive but rare. The tips of hairs can provide good information about how the hair has been treated. Scissor-cut hair has a clean, straight border, whereas razor-cut hair is angled, as depicted in Figure 1. In a hit-and-run incident or an explosion, flying glass cuts hair in a unique way, leaving a long curved “tail.” Burned hair is blackened and may appear bubbled or expanded. Crushed hair is also easy to recognize. Bleaching of the hair oxidizes the pigmentation and removes its color. The treat ment may stop at this point or a new color may be added to the hair. Coloring hair is much like dyeing wool fibers (both are hair) or other textile fibers. As the hair con tinues to grow, the point where the bleaching/coloration was applied is visible as an abrupt color change, as shown in Figure 2. If the length of the natural hair color portion is measured, the examiner can make an estimate of the time interval between the cosmetic treatment and the time the hair was lost. Head hairs grow an average of 1/2 in (1.3 cm) per month, so the natural portion length in inches would be multiplied by 0.5 to yield the approximate number of months. The diseases that affect the hair morphology are rare, but this makes them excel lent evidence for identifying a source. Pili annulati refers to hairs with colored rings. In pili annulati, the hair has alternating light and dark bands along its length, like tiger or zebra stripes. People with dark hair may have pili annulati but not know it because their hair color masks the condition. Monilethrix makes hairs look like a string of beads (the name comes from the Greek words for “bead” and “hair”). Along the length of the hair are nodes and constrictions making the hair vary in diameter. This hair beading weakens the hair, and people suffering from monilethrix have patchy hair loss. Pili torti is, as the name suggests, a twisting of the hair along its length, creating a spiral morphology. There may be several twists in one hair. The cuticle is present, but the twisting creates stress that leads to fractures in the cuticle and cortex. Vermin (such as lice), dandruff, or fungus may also be present on hairs, and this fact should be noted. These factors add to the classification of the hairs as coming from individuals with these traits. Misconceptions abound about hairs and what can be derived from their examination. Age and sex cannot be determined from looking at hairs; gray hairs may occur from a person’s 20s onward, and long hair doesn’t mean “female” just as short hair doesn’t mean “male.” Hairs do not grow after people die (how could they?)—the skin shrinks from loss of water, making the hairs more prominent (likewise with nails). And, some studies to the contrary, shaving does not stimulate hair growth.
FIGURE 1 The tips of hairs can provide good information about how the hair has been treated. Scissor-cut hair has a clean, straight border, whereas razor-cut hair is angled. In a hit-and run incident or an explosion, flying glass cuts hair in a unique way, leaving a long curved “tail.” Singed hair is blackened and may appear bubbled or expanded. Split tips may be due to cosmetic treatment or weakened hair.
FIGURE 2 Coloring hair is much like dyeing wool fibers (both are hair) or other textile fibers. As the hair continues to grow, the point where the bleaching/coloration was applied is visible as an abrupt color change. This hair has been bleached.
