How Long Does THC Stay In Your Hair? The Correct Answer Is Here!

Hair THC testing is a typical way lab professionals test for drugs. It takes less time and is less invasive than urine and blood tests.

Accordingly, you will most likely regret or get in big trouble when you take the test if you have smoked before.

In theory, it should take about 90 days from exposure to the drug to THC get out of your hair. But exactly how long does THC stay in your hair?

Let me explain in this article if this is your primary concern!

THC Formation In Hair

How Long Does THC Stay In Your Hair 3
THC on hair

First, you need to understand how THC is formed and how it enters your hair. Remember that all you do when you smoke is allow compounds in the drug, like cannabinoids, to enter your bloodstream.

They’re in the veins at first, then they’ll travel through the bloodstream to other receptors in your body and begin to unbind for their actual effects.

During this process, some psychoactive THC metabolites enter the blood vessels that nourish the scalp’s cells. Compounds from marijuana, vaping, or whatever you smoke to travel through the bloodstream to a hair shaft through the papilla.

About three weeks later, new hair grows and carries THC stored in the scalp, which is also the main reason your hair contains THC.

Thus, you have grasped how THC forms and develops and how it appears in your hair. It’s time to know how long THC stays in your hair.

How Long Does THC Stay In Your Hair?

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THC in your hair

Many studies show that THC can be detected in your hair for 90 days from the last exposure to this chemical.

This timeframe results from multiple calculations based on how long new hair grows and carries THC in the scalp. It also includes, of course, the hair needed for sampling.

You probably already know about Quest Diagnostics, one of the leading drug testing labs in the United States.

They suggest it takes 5 to 10 days before the hair grows out of the scalp. In other words, every month, human hair grows about 1.5 inches.

Meanwhile, a THC sample will be taken from hair 1.5 inches from your scalp, so you need at least three months to make sure THC is gone from your head.

Factors That Affect How Long THC Stays In Hair

Many factors affect how long THC will stay in your hair. Much of this depends on how well you use it and how well the drug is metabolized. These factors include:

Body mass index (BMI)

Body mass index (BMI) is a factor that influences how long THC stays in the hair.

For instance, some people with a high BMI, with more body fat, will hold onto THC longer. In contrast, thin people get less THC in their hair for a long time.


Gender is another common factor, as it is strongly associated with body mass index (BMI). After all, women usually have higher body fat than men, which means their ability to metabolize THC is also slower. Therefore, this chemical will last long and be easier to detect when tested.

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The metabolism rate of the body

Usually, people with high metabolic rates can help reduce the duration of THC in the hair. When the body’s metabolism is fast, it enhances the ability to metabolize THC in the blood and shortens hair growth time.

Frequency and use method

If you don’t smoke regularly, you can get THC out of your hair sooner than long-time users. In addition, THC content and how it is absorbed are other essential factors that affect how long this chemical stays in the hair.

In other words, the higher the THC content in the drug, the longer it stays in your hair. Therefore, it will be easier to eliminate this chemical when using drugs than marijuana.


Last but certainly not least is genetics. Some people’s bodies contain a beneficial enzyme, variations that work to speed up the THC removal from their hair. Usually, the concentration of this enzyme is also considered a genetic trait.

Hair length

The length of hair can impact the time that THC stays in the hair. The longer the hair, the more time it will take for THC to grow out of the hair shaft and become undetectable.

How To Test THC In Hair?

How Long Does THC Stay In Your Hair
How to test one?

Indeed you are curious to know how research institutes and testing facilities test for THC content in hair, and the following information will be beneficial to you. Keep reading to understand.

After collecting the hair, the experts will wash it to remove any ingredients that affect the test results. Then, they will cut and treat the hair in a solution to break it down into the protein keratin and other compounds that can penetrate inside.

This solution will undergo ELISA screening, which uses molecular-binding antibodies. If the test results are positive, they will be in a second test with techniques such as GC/MS and MS/MS.

These are also known as gas chromatography and mass spectrometry. Although it is complicated to apply, this method gives more accurate test results. Next, they will scan the sample for the target compound’s molecular signatures, THC.

When the chemical concentration reaches 0.1 Picogram/milligram of hair, THC is present in your hair.


This article has helped you understand the question: How long does THC stay in your hair? THC stays in your hair for 90 days from your last use.

Since many factors affect its formation and growth in the body, it would be better to know the exact progress of the hair tests.

This information has helped you understand this toxin and how to test for them. If you have any questions, please send them to my email address.

I am always available to answer questions to help my readers have a better experience. Thank you for reading!

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