How Does a Hair Follicle Drug Test Work?

forensic hair test


A hair follicle drug test is used to screen for the abuse of prescription drugs, alcohol, or illegal substances such as cocaine. While blood or urine tests are typically more commonly used when testing for drugs, the hair follicle test has garnered some popularity in recent years.

A large part of the allure of the hair follicle test is that drugs remain detectable in your hair follicles for up to 90 days, which is longer than in your urine, blood, or saliva. It’s also able to pick up on patterns of use. For instance, if you had a history of drug abuse and recently started trying to get clean, it will pick up on that. The hair is required to be taken directly from a person’s head and not a comb or hairbrush to avoid the risk of contamination.

How Does It Work?

If you consume or use a drug, your body creates something called a drug metabolite. This is generated as your body breaks down the drug you’ve consumed. A hair follicle test is designed to pick up on this drug metabolite or the drug itself. You might find it curious that a drug you consume orally or through your nasal cavity can be detected through your hair follicles.

Anytime you consume a drug through any medium, it’s broken down by your body and finds its way to your bloodstream. From your bloodstream, it begins to make its way through your entire body and this includes your hair. It makes its way into your hair through the hair follicles and oil glands on your scalp.

These remnants remain in your hair as it grows. What this means is that these metabolites can remain in your hair for many months. The drug metabolite doesn’t just find its way to the hair on your head, but in other parts of the body you might find hair such as your armpits.

The process by which a drug makes its way to your hair does take some time, typically about seven to 10 days. That means a person with no history of drug use who very recently used a drug might not be able to have it detected through their hair.

Hair taken from your head will hold evidence of drug use for up to 90 days while hair taken from other parts of your body could hold evidence for up to a year. The most common type of hair follicle drug test is the 5-panel drug test. This test works to detect cocaine, opiates, PCP, THC, and amphetamines.

What to Expect During the Test 

The only thing a hair follicle drug test requires from you is a small patch of your hair. This sample will be collected by a lab technician from your head. While at-home hair follicle drug tests are available, it’s typically preferable for it to be handled by a technician to prevent contamination of the sample or interference with the testing process.

The sample is typically collected from an inconspicuous part of the head like at the back and is usually no thicker than a finger, and around one and a half to two inches long. For people who are bald or live with some sort of condition that causes hair loss, hair might be taken from another part of the body.

There’s no special preparation you need to do before the test, but you should supply the laboratory with a list of any prescription drugs you might be taking.

Why You Might Need One 

A hair follicle drug test might be conducted for a number of reasons, most commonly at the request of an employer or a guardian. These are the most common instances in which you might be asked to do a hair follicle drug test:

  • At an addiction recovery or rehabilitation center: A hair follicle drug test might be conducted intermittently when staying at these types of centers. This is done to ensure that you are making progress in your recovery and not relapsing at any point.
  • At work: A drug test could either be conducted routinely at a place you work or after an incident has been reported. Certain jobs are required by law to routinely test their employees for drugs.
  • Your doctor asked for one: Hair follicle drug tests are typically not requested by doctors, however, a doctor assisting in your addiction recovery might order one to get a better understanding of your history of drug use. One is more likely to see a pattern with a hair follicle test than blood or urine.
  • By a court order: People who are on probation for drug-related offenses will often be subject to routine drug tests during their period of probation. A hair follicle drug test might be used for this 

What Drugs Can Be Detected

A hair follicle drug test can detect the following drugs: 

How Effective Is a Hair Follicle Drug Test? 

Hair follicle drug tests are highly effective. However, in certain cases, external factors such as contamination of the sample could affect the results. Some research has also shown that hair color could affect the results. Substances like opioids and cocaine have been found to linger more in darker hair than lighter hair.

This means you might find higher concentrations of certain drugs in darker hair that might not necessarily correlate with the person’s drug use. Environmental factors could also affect the outcome of these tests. Substances in hair products you use or in dust particles in the air could stick to your hair and be detected by the test. However, the odds of this happening are low.

While compared to other drug testing methods, the hair follicle drug test has a longer detection time, it’s typically more expensive than other methods. The results also aren’t as readily available as saliva or urine tests, as they have a longer processing time.

Another advantage of the hair follicle drug test is that it’s very hard to cheat. Using shampoos or certain hair products will not prevent drugs from being detected. Research on the effectiveness of a hair follicle drug test has shown that it’s highly effective in detecting drug abuse.

7 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Toketemu Ohwovoriole
Toketemu has been multimedia storyteller for the last four years. Her expertise focuses primarily on mental wellness and women’s health topics.