In 2015, the federal Fixing America’s Surface Transportation Act (FAST Act) authorized the use of hair testing as an alternative to the urine drug testing required for commercial motor vehicle operators. However, also required that the Department of Health and Human Services (HHS) to prepare uniform standards for implementation of hair drug testing before this method could be employed by HHS certified labs. As of December 2017, no such standards have been finalized.

Despite this delay in the authorization process, many employers have opted to use hair drug testing as a part of their voluntary drug testing programs or in addition to any federally required testing.

What is Hair Drug Testing?

Hair drug testing is a specialized form of hair analysis designed to detect evidence of drug use by an individual. Sometimes called hair follicle drug testing, hair testing, or hair drugs of abuse testing, the procedure involves the microscopic analysis of specimens taken from the test subject’s hair sample.

What Hair Testing Is Not

Before we discuss the details of what hair drug testing is, let’s take a quick look at what it is not.

First, even though hair drug testing is sometimes called hair follicle drug testing, the follicle of the test subject's hair isn’t the part that is collected or tested. A person’s hair follicles, sometimes called roots, are located below the surface of his or her skin. The hair collected for hair drug testing is collected from above the scalp or other skin surface. (Learn more in, "Will you cut my hair or pull it from the root for a hair drug test?")

Next, a hair drug test isn’t used to detect immediate or very recent drug use or substance abuse. The test only detects drugs that have been metabolized and entered the bloodstream long enough previously to show up as part of growing hair. Only after the molecules of targeted drugs or drug metabolites have passed from the bloodstream into the cellular structure of the test subject’s hair will this test identify their presence. (Learn more in "Oral Fluid, Urine, and Hair Testing: What's the Difference?")

Finally, while past drug use can be identified with a hair drug test, specific dates and quantities used cannot be pinpointed using this method.

How Does Hair Drug Testing Work?

Hair begins its growth cycle beneath a person’s skin, sprouting from what is called a hair bulb. This hair bulb serves as the base of the follicle. The follicle anchors the hair to the skin, it is the hair’s root. Hair growth is controlled by the delivery of hormones and other substances to the hair bulb via the person’s blood.

It is this delivery system that enables hair to be a vehicle for detection of an individual’s drug use. Each strand of hair absorbs the chemicals, including drug metabolites that pass through the supporting hair follicle. Sweat absorbed at the base of the shaft can also introduce foreign substances into the hair. Once absorbed, those chemicals remain embedded within the hair cells and waiting to be discovered. The American Society of Addiction Medicine (ASAM) describes the details of this absorption process in its 2017 consensus statement, "Appropriate Use of Drug Testing in Clinical Addiction Medicine".

To perform a hair drug test, a sample is collected from the test subject. Most labs require a collection of approximately 120 strands of hair. To conduct a ninety-day assessment, the strands must be at least 1.5 inches in length. (Learn more in "Will you cut my hair or pull it from the root for a hair drug test?")

Once a properly collected sample is sent to the lab, it is washed to remove any external contaminants such as hairspray. The hair sample is then cut into small pieces or ground into a powder before being subjected to an extraction process. This process releases any targeted drugs or drug metabolites from the the hair, allowing it to be detected through use of one of several different screening methods. According to the Society of Hair "Testing Guidelines for Drug Testing Hair", gas chromatography-mass spectrometry (GC-MS) is often used for confirmatory hair drug tests.

Why Choose Hair Drug Testing?

Hair drug testing is unique among testing procedures because when performed properly using a sample of adequate length this testing method allows testers to assess a person’s drug use over time. While a hair sample will not reveal recent drug use, it will show evidence of past use. In most instances, a hair drug test will present the results of a seven to ninety-day window.

In comparison, a urine test detection window is limited to just seventy-two hours in most instance. An exception to this time limitation is the detection of marijuana use. THC metabolites may be detected for up to two weeks following exposure using a lab-based urine test. This "Drug Testing Options Summary" from LabCorp presents the different detection windows for urine, oral fluid and hair testing.

This long detection window is one of several reasons some employers and safety experts advocate the use of hair drug testing instead of or in addition to urine testing for pre-employment screenings. While a habitual drug user may be able to abstain from use long enough to pass a urine or oral fluid drug test, a hair drug test will identify his or her prior usage.

This was the reasoning behind the nation of Brazil’s decision to mandate “wide window of detection” tests for its professional driver screening program. Several U.S. based trucking companies also use hair drug testing in addition to the federally mandated DOT urine drug test to screen potential commercial driver. (Learn more in "DOT vs. Non DOT Testing: What's the Difference?")

Hair drug testing also eliminates the privacy and adulteration concerns that are associated with urine drug testing. (Learn more in "Top 3 Ways Employees Try to Cheat Drug Testing".)

What Do the Critics Say About Hair Drug Testing?

With the mounting call by employers in the transportation industry to adopt hair drug testing standards for DOT testing, why hasn’t the program moved forward? In short, because the process hasn’t earned favorable reviews from everyone and some of the concerns involve political hot topics. Questions about hair drug testing reliability and its potential to have a disparate impact on minorities remain.

The Substance Abuse and Mental Health Services Administration’s publication, "Clinical Drug Testing in Primary Care" notes several issues that call the effectiveness of hair drug testing into question. First, researchers know that substances in a person’s sweat can be absorbed into the hair shaft. Additionally, some researchers believe that drugs can be introduced to the hair through environmental exposures. Others doubt that all traces of environmental exposure can be removed from the outer surface of the hair via washing.

The SAMHSA publication also raises concerns about the potential for disparate treatment due to biological differences between different hair types and colors that can affect the accuracy and detection window of the testing. Privacy advocates may be concerned about intrusion into personal behaviors away from the workplace as well. Finally, like other methods of drug testing, hair drug testing has been met with a contingent of countermeasures from specialized shampoos to recipes for hair treatments designed to help users avoid detection. (Learn more in "Hair Follicle Drug Testing 101".)

Is Hair Drug Testing the Right Choice for Your Organization?

Every type of drug testing has its pros and cons. Employers who must conduct DOT testing can only use hair drug testing as a secondary test, it is not a replacement for urine testing under the regulations. However, for employers seeking to avoid habitual drug users who may be able to dodge detection by urine drug tests, additional testing may be a wise investment.

As advocates for the test grow more impatient for HHS to act, the issue of whether hair drug testing is a reasonable alternative is sure to remain in the spotlight. At least, that is, until a better method comes along.