How Hair Follicle Drug Testing Works


Sober Recovery Expert Author

Have you taken drugs within the past 90 days? If so, hair follicle drug testing would reveal this. Why is hair follicle drug testing used? Because it is fast and accurate and can detect a person’s recent history of drug use more reliably and accurately than a urine test or saliva drug test might.

Many drugs are flushed or excreted from our body systems quickly, and are virtually undetectable in urine or saliva after 72 hours. However, tiny traces of drug molecules can remain inside your hair shaft for up to three months, and still be detectable in a lab test.

Hair follicle drug testing is fast and accurate and can detect a person's drug use in the last 90 days more reliably and accurately than a urine test or saliva drug test. Learn how it's used and what it can detect.

When Hair Follicle Drug Testing Is Used

Many employers and organizations conduct mandatory drug screenings, whereby prospective employees or participants consent to it as a condition of employment or enrollment in a program.

Mandatory drug testing of employees is utilized in several industries, including some areas of government, healthcare and transportation, where illicit drug use might lead to problems with safety and security. Some companies use hair follicle drug testing as part of the background check and comprehensive screening of new employees, while other companies use this type of drug testing randomly or periodically to screen even longtime employees.

An employer or organization can typically only request a strand of hair for drug testing after receiving a signed consent. Some parents who are concerned about their teenager’s drug use, however, might collect some strands of hair from their child’s pillow and submit the samples for drug testing without prior consent.

How Hair Follicle Drug Testing Works

Hair follicle drug testing requires a sample of hair—generally several strands will be required. Sometimes hair samples must be collected from different areas of the head in order to provide a sufficient sample for the test. Once collected, the hair sample will be sealed in an envelope and submitted to a laboratory that conducts hair follicle drug testing. The lab specialists will test the hair sample for trace amounts of drugs that were absorbed into the hair follicles.

How is this possible? Your hair growth is stimulated by the flow of blood into your head and scalp. When you ingest drugs, they enter your bloodstream and flow through your body via your circulatory system, including into your scalp and hair. Drugs you have ingested won’t show up in your hair right away, however. It will take about 10 days for any hair that has absorbed the drugs to grow above your scalp (and hair grows at a rate of about ½ inch per month).

Once the drug molecules are absorbed into the hair shaft from your bloodstream and become embedded inside the hair follicle, they cannot be washed out. No amount of shampooing or otherwise treating your hair with chemicals and other products from the outside can remove or change those molecules that got trapped inside your hair follicles. In other words, it can be difficult—if not impossible—to tamper with a hair follicle drug test.

Traces of many different types of drugs can remain inside the hair follicles for up to three months. That is true of the hairs that grow on your head. Traces of drugs can also remain inside hair follicles from your body hair, and for a longer period—in some cases, up to 12 months. Testing of body hair is also conducted by some laboratories, but that type of testing is not as reliable for determining when a drug was ingested.

Results of hair follicle drug testing can usually be seen in 24 to 72 hours. The lab will typically send a written report of the results within one to three business days to the employer or person who requested the test. Some drug testing laboratories also offer a phone service where the individual or authority who requested the test can call in after roughly 72 hours and enter a special account number to retrieve the test results over the phone.

Types of Drugs Hair Follicle Drug Testing Can Detect

Some of the drugs that hair follicle drug testing can detect include:

  • Marijuana
  • Opiates (i.e. Morphine, Codeine, Oxycodone, Hydrocodone)
  • Amphetamines (i.e. Methamphetamines, Ecstasy)
  • Phencyclidine (PCP)
  • Cocaine

Hair follicle testing is available for some other drugs and substances, including nicotine, methadone, benzodiazepines, and some tricyclic antidepressants, though tests of these drugs are somewhat more challenging and, therefore, less reliable.

Hair and External Exposure to Drugs

Many people ask if their hair can absorb drugs or substances, such as nicotine or marijuana smoke, externally from their environment. This may be possible to a certain degree, but most labs will use testing methods that distinguish between external exposures to drugs vs. internally metabolized drugs (those that were ingested or used).

If you or someone you know is seeking help from addiction, please visit our directory of treatment centers or call 800-772-8219 to start the path to recovery today.

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