Hair Follicle Drug Testing – What You Need to Know

A hair drug test is toxicology testing that measures the presence of drugs and their metabolites in a hair sample. Typically, a lab technician facilitates the process by cutting and shaving a small section of hair close to your scalp.

While urine tests can only indicate recent substance use, hair drug tests help evaluate usage patterns over an extended period. These tests are frequently used in safety-sensitive industries like transportation or construction.

The Sample

Hair drug tests use a sample of a person’s hair taken as close to the scalp as possible. The model needs to be at least 1.5 inches long and thick enough to detect drug usage within the past 90 days.

Drugs enter the bloodstream through a vessel in each hair follicle, and traces of those drugs can show up on a test for drugs that you’ve consumed recently. These traces are known as drug metabolites, and they’re detected when your hair is tested for drug use.

A hair drug test can go back about 90 days in your history of drug consumption, but it cannot identify the exact date that you used a specific drug. In addition, it isn’t easy to mask a positive test result by washing your hair before submitting a sample. That’s because drug metabolites tend to bind with melanin, and they won’t come off quickly. The only way to get a clean, false-negative result is not to use the drugs that were tested for. Therefore, a hair drug test is often followed by a urine test for confirmation.

The Test

When a person uses drugs, they pass through the bloodstream and into the hair follicles. The drug molecules bind to the hair shaft and are left behind when the bristles disappear or get washed. In addition, a hair follicle drug test can detect traces of those metabolites. The sample for the test is a section of hair about an inch and a half long cut close to the scalp, typically by a laboratory technician. Enzyme-Linked Immunosorbent Assay (ELISA) methodology screens the sample for drug use. Any nonnegative tests are sent for confirmatory gas chromatography/mass spectrometry (GC-MS) testing.

Unlike urine drug testing, which has a limited window of detection, hair follicle testing can identify historical drug use up to 90 days in advance. It’s also nearly impossible to cheat with a hair test because specimen collection can be observed, and there are no known methods for adulterating the sample. In addition, employers must follow specific pre-employment drug screening laws. Read on to learn more about how a hair drug test works, its detection period, and relevant hair testing laws.


A hair sample can detect drug use or misuse within a 90-day timeframe and is often used by employers to screen job applicants. It can also be used by courts and addiction treatment centers to monitor substance abuse. However, it is harder to interpret than urine and blood tests because drug metabolites may transfer from the body to the hair shaft during sleep, exercise, or even by touching one’s hands. For example, if someone enters a room where people are snorting cocaine, the metabolites from the drug may end up in their hair even though they did not use or ingest the drug themselves.

A sample of a person’s hair is collected, usually near the scalp, and sent to a lab for testing. A hair follicle drug test can detect evidence of illegal drug use or prescription drug misuse in a 90-day timeframe, and it is difficult to tamper with. However, the test cannot identify the exact date of drug use or tell how often drugs were used. It can also produce false positive results from environmental exposure and is not 100% accurate.

False-Positive Results

Hair follicle drug tests provide a broader detection window than urine or blood testing. They are ideal for examining substance use patterns over an extended period. They are usually conducted in professional and safety-critical industries such as construction, manufacturing, trucking, and transportation.

A hair sample can detect the presence of drugs consumed up to 90 days ago. This lengthy detection window is due to how drug metabolites are incorporated into hair growth. Drugs are absorbed into the blood vessels that feed the hair follicle and pass through it as it grows, leaving traces of drugs in the resulting hair.

The results of a hair follicle drug test can be inaccurate if the sample is contaminated or the individual has been using a shampoo or product that cleanses hair-containing drugs. This is why follow-up testing (often utilizing a different test method) is essential after the initial drug test. Also, hair treatments such as bleaching, dyeing, and shampooing can significantly alter a sample’s concentration of drugs and metabolites.

Follow-Up Testing

Hair follicle drug testing is a popular method of screening for recreational drug use and misuse of prescription medications. The test analyzes a small section of hair cut close to the scalp and can detect drug use within 90 days of specimen collection. Hair samples are easy to obtain, nearly impossible to cheat, and meet the same reference standards as urine tests. The test also allows a more in-depth look at an individual’s past substance use and provides the ability to identify periods of abstinence.

Hair treatment chemicals like shampoo, bleach, and relaxers can alter the concentration of drugs and metabolites detected during a test. Therefore, a hair sample should be taken from a part of the head that has yet to be treated.

Some drugs are difficult to detect with a hair test because they can travel up the hair shaft. For example, cocaine, amphetamines, and opioids can be deposited in the scalp’s skin cells and may not be absorbed by the hair follicle. This can make it hard for those who are accustomed to heavy drug use to maintain abstinence for one week or less, as would be required to pass a standard urine test.