What are the limitations of a hair follicle test?

Author: Prof. Carole McGlynn I  |  Last update: Wednesday, September 3, 2025

An often-unacknowledged limitation is that exposure to psychoactive substances is typically not detectable within the first 1–2 weeks post-exposure. Therefore, while hair can allow us to detect exposure to substances within a wide window of time, it typically does not allow us to detect very recent use.

What can mess up a hair follicle test?

There are many factors that have the potential to impact the results of a hair drug test, including:
  • Hair treatments, such as bleaching, dyeing, perming and straightening.
  • Hair colour.
  • Hair growth rate and length of hair available.
  • Environmental factors, such as passive exposure to drugs.
  • Attempting to 'cheat' the test.

What is a major drawback with hair analysis?

Hair testing has several drawbacks, including a small detection window, false positive results, outside variables that can alter accuracy, a high cost, and challenges interpreting the results. Additionally, there is a risk of prejudice, a breach of privacy, tampering, and a lack of uniformity with hair testing.

How often are hair follicle tests wrong?

In fact, it is estimated that over 15% of all hair drug test interpretations will yield inaccurate results - a worrying figure that could have huge implications for your client. It might sound counterintuitive, but positive doesn't always mean positive, and this is where complications emerge.

How sensitive are hair follicle drug tests?

Specificity of hair testing at standard laboratory cut-offs exceeded 90% for all drugs, but sensitivity of hair testing relative to self-report was low, identifying only 52.3% (127/243) of self-disclosed marijuana users, 65.2% (30/46) of cocaine users, 24.2% (8/33) of amphetamine users, and 2.9% (2/68) of opioid users.

The Hair Follicle Drug Test: Myth Vs. Fact

How reliable is hair analysis?

Hair analysis provides good evidence in the fields of forensic and clinical toxicology, doping control, and occupational medicine, but do not demonstrate clear evidence in the fields of general health screening.

Can a hair follicle test detect infrequent use?

Given adequate hair length, hair testing can detect exposure to psychoactive substances within wide time-frames – much wider than with urine, blood, and saliva. However, hair testing cannot detect very recent exposure, and infrequent cannabis use in particular can be difficult to detect.

How long before I can pass a hair follicle drug test?

How far back can a hair drug test detect drug use? Hair drug tests have the longest detection period, and can typically detect drug use for up to 90 days. Depending on the drugs used, a hair sample can sometimes help determine when drug use occurred and whether it's been discontinued.

Does peroxide remove drugs from hair?

Here, we show evidence that peroxide treatment can, even after 15 minutes, completely remove incorporated cocaine and degradation products from the hair, making it impossible to identify cocaine users by hair analysis.

Can a hair follicle test be fooled?

In theory, hair drug tests can be attempted to be cheated or manipulated, but it's not easy to do so effectively. Hair drug testing is considered tamper-resistant, which means that it is difficult to manipulate the results of the test.

What Cannot be determined by hair analysis?

Given how often most people cut their hair, hair analysis generally will not tell you anything about exposures that occurred more than one year ago. Furthermore, for most chemicals, hair analysis cannot tell you where a chemical in your hair came from.

What is the window for hair drug test?

Hair follicle drugs of abuse testing offers up to a 90-day window for detection of drug use and a convenient collection process that can be performed almost anywhere.

How accurate is a hair follicle drug screen?

Although hair samples undergo a two-step testing process, they are not 100 percent accurate. Factors that can affect the concentration of drug metabolites present in a hair sample can include: the structure of drug compounds. the quantity of drugs a person has consumed.

How can you fail a hair follicle test?

Factors that affect test results include: Environmental exposures: Inaccurate results can also occur due to environmental exposure to drugs. For example, during ​​exposure to secondhand smoke from cocaine or tobacco some of the smoke or vapor can enter the hair and lead to a positive test result.

Can you dye your hair to pass a hair follicle test?

Hair drug testing on dyed or bleached hair may still be worthwhile. Any chemical treatment such as hair dye, bleach, chemical straightening and permanent waves can damage the hair. This damage may lead to some of the drugs that may be present, being leached out from the hair.

What do employers look for in a hair follicle test?

Hair drug testing can detect a variety of drugs including, but not limited to: marijuana, cocaine, opioids (including codeine, morphine, heroin, and synthetic opioids), methamphetamine, ecstasy (MDMA), and PCP.

What can cause a false positive hair follicle test?

An evidentiary false positive that is the result of exogenous exposure to drug(s) in the environment. The drug positive result is not due to the ingestion or use of drug by any route of administration. Drug(s) in sweat or sebum from a source other than the user contacting hair to cause a drug positive result.

What is the jerry g method?

The Jerry G Method involves using bleach and hair dye to remove any drug metabolites from the hair follicles. These harsh ingredients can forcefully open your hair follicles to clear any traces of marijuana and other drugs.

How long does it take to detox your hair?

For others, their hair detox journey can take about 14 days. There are a few factors that might affect the length of your detox: It could depend on your specific hair type, environmental pollution, the level of buildup you have from dead skin cells and styling products, and how frequently you wash your hair.

Can a hair test detect one-time use?

The use of a drug on one occasion only would not be expected to give rise to positive results as insufficient drug would be expected to accumulate in the hair to be detected above the cut off level. This is because almost all of the hair analysed would cover a time when drug use had not occurred.

Can eyebrows be used for a hair drug test?

Hair drug test collection

If the donor does not have head hair or if their hair is less than a ½ inch long, a specimen can be taken from other locations on the body. In order of preference, our collectors will cut the chest, underarm, leg, or facial hair to obtain a sample.

What affects hair follicle drug test?

Factors Affecting Hair Test Accuracy

These include outside variables like hair care products, certain practices, scalp issues, hair length, and the substance being tested for. The accuracy of the results is also affected by the laboratory performing the test and the technique utilised to examine the material.

Can a hair follicle test be manipulated?

Intentional hair manipulation to avoid positive drug testing mainly relies on forced washing-out effects (“dilution of the hair”), for example, through extensive washing or even the use of commercially available cleansing shampoos advertised to produce negative hair testing results.

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