Hair Drug Test Method: How Labs Collect, Wash, Screen and Confirm a Hair Sample, Step by Step

Updated 18 Oct 2026 · By the DrugTestAnswers editorial team

A hair drug test is less mysterious than it sounds. A collector cuts a small lock of hair near the scalp, the lab washes it to remove anything sitting on the outside, then dissolves or soaks it to pull out drugs locked inside the strand. A quick screen flags anything suspicious, and a mass spectrometry test confirms exactly what it is and how much. Here is each step in plain words, what the numbers on a report mean, and the things that can change what the lab finds. We may earn a commission if you buy through our links.

How drugs get into hair

When a drug is in your bloodstream, small amounts pass into the hair follicle and get built into the strand as it forms. Some may also come from sweat and skin oils coating the hair. Once locked into the keratin, the drug moves up with the growing hair. Head hair grows roughly half an inch a month, which is why a standard 1.5 inch sample cut at the root is read as roughly the last 90 days. Drugs also bind to melanin, the pigment in hair, which is one reason darker hair can hold more of some drugs.

Step 1: Collection and chain of custody

1. ID check and paperwork. The collector confirms who you are and starts a custody and control form that follows the sample to the lab.
2. Cutting. Hair is cut as close to the scalp as possible, usually from the crown, often from more than one spot so no bald patch shows. Labs ask for a set weight, commonly described as a lock about the width of a pencil.
3. Marking the root end. The collector lines the hair up so the lab knows which end grew most recently.
4. Sealing. The sample is wrapped in foil, placed in an envelope and sealed with tamper-evident tape that you initial.

If head hair is too short, the collector takes body hair instead and notes where it came from. See which body hair can be used for drug testing.

Step 2: Decontamination washes

Before testing, the lab washes the hair, often with a sequence of solvents and buffer solutions. The goal is to remove drug that is only on the surface, such as smoke or residue from handling, so the result reflects what was taken into the body. Some labs test the wash liquid too and compare it with the hair result. This step is a big reason labs say outside exposure alone rarely causes a positive, although it remains a debated topic for drugs like cocaine and marijuana smoke.

Step 3: Cutting and extraction

The washed hair is cut into tiny pieces or ground into powder, then weighed. Drugs are pulled out with one of several approaches: soaking in a solvent such as methanol, digesting the hair with an acid, base or enzyme, or a combination. The method depends on the drug and the lab. The weighed amount matters because results are reported per milligram of hair.

Step 4: The screen

Most labs run an immunoassay screen first, commonly an ELISA (enzyme-linked immunosorbent assay). It uses antibodies designed to react with a drug class, like amphetamines or opiates. Screens are fast and cheap, but they can react to related compounds. A result below the screening cutoff is reported as negative. Anything above it is called a presumptive positive and moves to confirmation.

Step 5: Confirmation by mass spectrometry

A presumptive positive is retested using gas chromatography or liquid chromatography combined with mass spectrometry (GC-MS or LC-MS/MS). These instruments separate the compounds in the sample and identify them by their molecular fingerprint, so they can tell methamphetamine from a cold medicine, or a prescription drug from a street drug. Only results confirmed at or above the confirmation cutoff are reported as positive. For marijuana, labs usually confirm THC-COOH, a metabolite the body makes, because finding it shows the drug was processed in the body rather than just landing on the hair. Our guide to screen vs confirm results covers this two-step logic in more detail.

Cutoffs: what pg/mg means

Hair results are tiny amounts, reported in picograms per milligram of hair (pg/mg). A picogram is a trillionth of a gram. Each drug has its own screening and confirmation cutoff, set by the lab or by guidelines from groups such as the Society of Hair Testing. Cutoffs for marijuana metabolite are far lower than for drugs like cocaine because THC-COOH builds into hair in very small amounts. A result just above or below a cutoff doesn't measure how impaired someone was; it shows whether the amount found crossed the line the program uses.

Segment testing

Because head hair grows at a fairly steady rate, a longer sample can be cut into sections, for example half-inch pieces, and each tested separately. That gives a rough timeline of use month by month. Segment testing is more common in legal and clinical cases than in routine job tests, and it doesn't work for body hair, which grows unevenly.

What can change what the lab finds

• Hair color. Darker hair has more melanin and can hold more of some drugs, such as cocaine and amphetamines.
• Cosmetic treatments. Bleach, perms, relaxers and some dyes damage the strand and have been shown in studies to lower drug levels, though by unpredictable amounts. See hair dye and hair tests.
• Washing and products. Normal shampooing doesn't do much to drug locked inside the hair. Detox shampoos claim more, but there is no independent published proof they work.
• Amount and frequency of use. Heavy or regular use leaves far more in hair than a single use.
• Timing. Hair takes about a week to grow past the scalp, so very recent use often isn't in the sample.

Product facts: Old Style Aloe Toxin Rid

Understanding the method is why many people end up looking at deep-cleansing shampoos. The most common is Old Style Aloe Toxin Rid from TestClear.

• What TestClear says: a deep-cleansing shampoo designed to remove buildup and residue from the hair.
• Maker's directions in short: wash first with regular shampoo, then apply Aloe Toxin Rid to damp hair and scalp, leave it on 10 to 15 minutes and rinse, repeating over several days before a test.
• What is not proven: given how deep drugs sit in the strand and how labs wash samples, no independent published study shows it gets anyone past a hair drug test. Treat reviews as anecdotes.

If you want to read more, you can see Old Style Aloe Toxin Rid at TestClear, and our Aloe Toxin Rid review and how-to guide covers directions and schedules.

Home hair tests use the same lab steps

Home hair kits don't give you an instant answer. You cut the sample yourself, mail it to a lab, and it goes through the same washing, screening and confirmation process. That makes them a useful preview before an official test. Compare kits in our guide to the best hair follicle drug test kits.

Our sourcing

Collection, decontamination, extraction and confirmation methods come from published forensic toxicology literature and Society of Hair Testing guidance. Product directions come from TestClear's product page. We don't run lab tests or publish testimonials; see our editorial methodology.

Tests this page doesn't apply to

Don't use any product or routine on this page to try to affect a DOT-regulated test, FAA aviation testing, federal employee programs, military testing, or court, probation and parole testing. Tampering with those can count as a refusal and may be illegal.

Disclaimer and help

Informational only, not medical or legal advice. Tampering with a drug test may be illegal and can count as a refusal or failed test. The only guaranteed way to pass is abstinence. For free, confidential support 24/7, call the SAMHSA National Helpline at 1-800-662-4357. If you're in crisis, call or text 988.