Tox Tuesday: Hair testing

iStock_000011990202XSmallSometimes knowing what drugs a person has had in their system can be discovered by looking at the hair on his or her head or body.

Hair testing for traces of illicit substances is utilized in a range of cases and has some advantages over other types of tests when it comes to specific uses. When compared to blood or urine drug tests, hair tests typically can provide a longer-lasting record of drug use because certain substances leave traces in hair follicles. It’s this trait that has the attention of the World Anti-Doping Agency (WADA), which announced in December that it may use hair testing to combat doping in sports.

Research has indicated that drugs may be incorporated into hair in several ways, including blood to the growing follicle, from the surrounding external environment and from gland secretions1. Interestingly, the amount of melanin (or pigment) in hair plays a significant role in how much drug is retained (in one study, dark hair retained more PCP than lighter hair2). This leaves a record in the hair, which can then be analyzed via several different methods, including enzyme-linked immunosorbent assays (ELISA)3. It is important to note that a key part of drug detection using hair samples is the ability to differentiate between environmental exposure versus actual drug use.

Hair can be less invasive to collect than other matrices, which makes it a good sample type for use in workplace drug testing or drug treatment programs.  It also can be resampled if results are inconclusive (so long as the hair hasn’t been removed since the original sample was taken) and can be used in post-mortem analysis, Forensic Magazine notes.


1 Henderson GL. Mechanisms of drug incorporation into hair. Forensic Sci Int. 1993 Dec; 63 (1-3): 19-29. Retrieved from

2 Slawson MH, Wilkins DG and Rollins DE. The incorporation of drugs into hair: Relationship of hair color and melanin concentration to phencyclidine incorporation. J. Anal. Toxicol. 1998 Oct; 22: 406-413

3 Pujol M, Cirimele V, Trirsch PJ, Vaillain M and Kintz P. Evaluation of the IDS One-Step™ ELISA kits for the detection of illicit drugs in hair. Forensic Sci Int. 2007. 170: 189-192

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