Drug testing is a common practice in the modern workplace, used for both pre-employment screening and random checks of current employees. While many people are familiar with traditional methods, the hair follicle test is an increasingly used technique that concerns job seekers and workers alike. This method is becoming more common in certain high-risk and regulated sectors for its distinct advantages over other testing types.
Why Employers Choose Hair Testing
Employers use hair testing because it offers a significant advantage in reliability and long-term detection compared to other methods. The collection process is supervised and involves cutting a small sample of hair near the scalp. This makes it extremely difficult for an applicant or employee to substitute or tamper with the specimen, providing employers with greater confidence in the integrity of the results.
The test is valued for its ability to reveal patterns of repetitive drug use over a long period. This longer look-back capability is preferred by companies hiring for safety-sensitive roles where substance use poses a liability risk. Consequently, industries such as transportation, government contracting, oil and gas, and financial services often incorporate hair testing into their protocols. The test serves as a deterrent to drug use, helping to mitigate risks associated with accidents and lower productivity.
The Science and Detection Window
The mechanism behind hair testing relies on the body’s metabolic process after a substance is consumed. Once a drug enters the bloodstream, the parent drug and its metabolites circulate throughout the body, eventually reaching the hair matrix at the base of the hair follicle. As the hair shaft grows, these drug compounds become chemically incorporated and permanently trapped within the hair’s keratin structure.
This incorporation creates a historical record of drug use that grows out from the scalp. Since human head hair grows at a consistent rate of approximately half an inch per month, a standard sample of 1.5 inches provides a detection window of 90 days. This contrasts sharply with the narrow window of a urine test, which typically only captures drug use from the previous one to three days.
Analysis often utilizes confirmatory techniques like Gas Chromatography/Mass Spectrometry (GC/MS) to isolate and identify the trapped metabolites. A limitation is that it takes time for the hair to grow past the scalp, meaning drug use within the last seven to ten days may not be detectable. The test is not designed to show current impairment, but rather to establish a pattern of use over the preceding three months.
Legal Considerations for Workplace Hair Testing
The decision to use hair testing is often determined by a patchwork of federal and state laws. While federal agencies like the Department of Transportation (DOT) generally mandate urine testing for safety-sensitive positions, private companies often have the discretion to use hair tests. They must adhere to state-specific regulations, which govern how and when drug testing can be conducted, including procedural requirements for notice and consent.
Some states have placed restrictions on the use of hair testing, or any testing method, for certain substances. For example, laws in California now prohibit employers from discriminating against applicants based on tests that screen for non-psychoactive cannabis metabolites. Nevada was one of the first states to enact laws that curb pre-employment marijuana testing, though exceptions exist for safety-sensitive positions or those requiring a commercial driver’s license.
Employers must also navigate the Americans with Disabilities Act (ADA). The ADA protects individuals with a history of addiction who are no longer using drugs illegally. It requires that testing policies be applied consistently to all employees to avoid claims of discrimination. If a positive result is caused by a lawfully prescribed medication, employers must treat that information as a confidential medical record.
Accuracy Concerns and Challenging Results
Despite the sophistication of the process, hair testing is not immune to accuracy concerns. Drugs like cocaine, methamphetamine, and cannabis can adhere to the hair shaft from external sources, such as second-hand smoke or contact with contaminated surfaces. Reputable laboratories address this by performing a rigorous washing procedure on the sample to remove external contaminants before analysis.
To distinguish between passive contamination and intentional use, laboratories look for the presence of drug metabolites. Following a positive screening, a Medical Review Officer (MRO) reviews the result and contacts the applicant to explore any alternative medical explanations. An applicant who wishes to challenge a positive finding has the right to request a re-test using a portion of the original sample, known as a split sample.