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Cunning investigators use tresses to trace the behavior of criminals, anorexics, and people who drink water.

Cunning investigators use tresses to trace the behavior of criminals, anorexics, and people who drink water.


Untangling the Secrets of your Scalp

By Molly Wetterschneider

You don’t have to watch more than one or two episodes of the television show CSI to gather that forensic scientists glean quite a bit of information from a sample of hair collected at a crime scene. But those breakaway bristles can point out more than just the identity of a prime suspect. Hairs can also disclose what someone has been eating … or perhaps hasn’t been eating. A study published last month showed researchers could identify whether patients had anorexia or bulimia solely by analyzing hairs plucked from their heads. The results prompted SciTini to ask exactly what someone can learn about you from surreptitiously seizing a sample from your scalp.

A favorite identifying fiber of the crime scene investigator, hair can provide clues about a subject’s ethnicity. Criminalist Amy Kraatz of the Boston Police Department Crime Laboratory and her team consider three questions when examining a hair: Is it human or animal? What area of the body did it come from? And, what are the characteristics of the person? To distinguish race, Kraatz uses a light microscope to look at the shape of a strand’s cross-section and its pigment distribution throughout the shaft. Caucasian hairs have an oval-shaped cross-section and an even pigment distribution, African hairs are flat and have clumps of pigment, while Asian hairs are circular and streaked.

Forensic scientists can use hairs collected from a victim’s remains and compare them with hairs collected from hair brushes and clothing at home to identify the dead. Hair was just one of the bodily remains used to identify victims of the terrorist attack on the World Trade Center. However, while hair analysis can give many insights into the physical characteristics of a victim or suspect, Kraatz cautions that hair is not always a key identifier. Protocol dictates that she can say whether hairs “appear similar” using microscopic analysis, but she can’t give a quantitative description of her certainty without a DNA sample. Nuclear DNA extracted from the living root of a plucked hair can give a person’s unique DNA fingerprint, while mitochondrial DNA, which you inherit from your mother and which is found in the shaft of hair, can narrow down a suspect list to a small group of related individuals (a person, his or her mother and grandmother, and any siblings by that mother).

Criminal investigators may not be the only ones interested in what’s trapped in your tresses. Parole officers and potential employers can use hair to detect the use of cocaine, marijuana, heroin, and other illegal drugs. Not only is hair often easier to collect and handle than other identifiers such as urine, it tells more about prolonged use and more about less recent use than does a cup of pee. Because hair grows at a steady rate of one centimeter per month on average, researchers can determine when along the hair shaft detectable activity occurred. Like stock numbers scrolling on an old-fashioned ticker tape, recent information is found at the base of the hair, near the scalp, while the free tip of the hair reveals older data.

The truly paranoid and less criminally inclined reader may be thinking, “But I don’t do drugs or visit crime scenes. Is my hair boring?”  Perhaps so, but researchers can tell a lot about even mundane activities from just a small lock of hair. Two main areas of research focus on the proteins that make up the hair and trace elements absorbed from food, water, or skin products—which the body excretes, or gets rid of, by building into hair.

Each day you shed about
one-hundred hairs.
(Ana Golpe)

You are what you eat, and so is your hair. Because hair is made up of protein, it can tell a lot about a person’s diet. Last month, researchers at Brigham Young University published a study describing how they looked at isotopic ratios of carbon and nitrogen in hair proteins to determine eating disorders. Using mass spectrometry, a technique that identifies the amount of atoms of specific elements in a sample by comparing and sorting them by mass, the researchers analyzed samples of five hairs from each experimental subject to determine the ratio of nitrogen-15 to nitrogen-14 isotopes and the ratio of carbon-13 to carbon-12. These ratios differ in carnivores and herbivores, as well as in severe anorexics whose main source of protein comes from the breakdown of their own tissues. Kent Hatch, an ecologist and the anorexia study’s lead author, has also used hair isotope ratios to determine how much meat bears eat in different parts of Utah.

Sure, a hair sample is the best way to ask a bear what he had for breakfast last week. But, using hairs to assess human health—particularly in sensitive arenas such as eating disorders—can raise many concerns. Keeping track of the correct hairs and collecting them effectively can play a role in the accuracy of results. Also, Hatch cautions that even with experts harvesting the hair samples, the test in his study is accurate only 80 percent of the time. “The way you would use the test is with people you already suspect have an eating disorder,” he says. For example, you might use this test for a loved one who is trying to hide an eating disorder and exhibits other signs, or a doctor might use it to check whether a patient who has left the controlled environment of a treatment clinic is maintaining a healthy diet.

Trace amounts of some elements found in hair can also disclose other habits. Stephen Haswell, a Professor of Analytical Science at the University of Hull in the United Kingdom, looks at mercury, chromium, magnesium, calcium, and about a dozen other elements in hair for clues about the source of water someone drinks, whether they have recently undergone dental work, their gender, and what kinds of cosmetics they use. Haswell says that you can often tell which region of the world someone lives in based on how hair reacts with the differing chemistries of regional tap waters. He cuts up the hairs into one-centimeter-long segments and mixes them with acid to break down the proteins and dissolve the elements in question. Keeping track of where along the shaft the slice of hair came from, he can use the slices as a time-delay measurement of when the body consumed the elements. “In theory, you could tell when someone had gotten their teeth done,” says Haswell. In 2003 study, he found that he could identify whether a mother had recently had her teeth filled by analyzing hairs removed from her newborn baby.

So you screen your calls, shred your mail, and keep your blinds closed to avoid those spying eyes. But, what can you do about all that telltale hair you leave around town?  Bleaching, dying, and shaving your locks is a good start, but even a covert coiffure still might fail to dissuade those snooping hair analysts from seeking out your scalp’s secrets.


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