Our hair doesn’t just make us feel and look good, it’s also like a hard drive that doesn’t forget anything. Forensic toxicology makes especially good use of these properties.

When it comes to “hair analysis,” your thoughts may stray to the dark world of crime or the last murder mystery you saw on TV. A hair was found at a crime scene, examined and matched, and the perpetrator was arrested. Case closed. But it’s not as simple as that. And it’s not a Hollywood invention either. As early as the end of the 19th century, doctors carried out the first microscopic examinations of hair to obtain forensic information. 

A criminal tip: if you want to find out the positive significance of a hair analysis, you’d be better off not combining the search terms “FBI + hair analysis.” If you do, you’ll probably lose faith in the results this kind of analysis produces. 

For many years, the FBI examined the hair of suspects under the microscope. As part of this purely morphological method, the hair was examined from the outside and assessed and compared by color and scale structure. By today’s scientific knowledge, this “evidence” would not have held much weight. Many verdicts would probably have been different. 

Hair is a biomonitor 

Since science and research never sleep, there are now methods and examinations that can tease the relevant information out of the hair. DNA also plays a key role now. Unthinkable back then.

Hair analysis has established itself primarily in the field of substance and abstinence testing. It allows laboratories to determine whether drugs, medication or alcohol have been consumed in recent months. In such cases, hair serves as a kind of tachograph that stores and documents the substances. This is possible because the hair root is in direct contact with the bloodstream and can absorb the ingredients. Traces of the substances in the blood are stored in the hair matrix, so anyone hoping to trick this type of test has only one option: get a razor and shave off all the hair on your body. 

Hair growth can be used to detect the consumption and/or abuse of certain substances over several months. This differs greatly, for example, from blood and urine samples taken during traffic checks (driving under the influence) or tests done after sports competitions to combat doping. While blood results offer a snapshot, urine results cover a period of one to three days. Only hair proves the presence of certain substances over several months, serving as a kind of long-term record. Whether the agents/substances entered the body via the mouth, nose or directly via the vein – it doesn’t matter. 

How does this kind of investigation work? 

The Center for Forensic Hair Analysis at the Institute of Forensic Medicine, University of Zurich, describes the laboratory process as follows: “The hair sample is washed several times to remove sweat, body fat or fine deposits such as cannabis smoke or cocaine residue. The sample is then crushed and pulverized. The next step is to remove the substances to be detected from the hair matrix. The hair powder is added to an extraction agent. Under constant shaking, deposited substances are released from the hair fragments. Highly specific laboratory analysis equipment determines whether and how intensively the substance was consumed.”

In addition to all the advantages that hair analysis offers, there are a number of disadvantages to consider. The Department of Forensic Toxicology/Hair Analysis at the Institute of Forensic Medicine, Charité Berlin, summarizes these as follows: 

“The physiology of hair growth results in a temporal uncertainty that arises due to: 

• the intra- and inter-individual variability of hair growth, 
• the presence of catagen and telogen hair, 
• the possible storage of substances from sweat or sebum, and 
• surrounding tissues. 

Furthermore, there is no inter-individual dose-concentration relationship. One-time consumption is usually not detectable, and the unprotected position of the hair allows for external contamination and manipulation.”

Hair analysis can also play an important role in the medical field. For example, it may be necessary to obtain information about abstinence prior to an organ transplant. Stress hormones such as cortisol can also be detected and quantified. This is important when it comes to preventing strokes. 

In recent years, there have also been many adverts claiming that you can identify possible nutrient deficiencies or harmful substances in your body by looking at your hair. Therapies and diets are then recommended or sold based on the results. Hair can tell us a lot, but it is not all-knowing. As the forensic experts from Zurich point out: “Hair analysis provides facts and figures – but no decisions delivered free to your door.” So, before you change your diet, take supplements or make any other important decisions based on a hair analysis, please consult your doctor. They will make the right decisions on your behalf. 

While it was too late for Napoleon or Ötzi the Iceman to visit a doctor, the two historically important men did have the “pleasure” of a hair analysis. People wanted to learn more about Ötzi’s lifestyle and eating habits to draw conclusions about the period in which he lived. In the case of Napoleon, we step back into the dark world of crime. Was he poisoned by arsenic, or did he die of stomach cancer? Scholars argue about this. As a side note, arsenic was used a long, long time ago in hair care and the external treatment of hair. Coincidence? Sometimes hair is simply a guardian of secrets.