Cannabis Science

How Long Does Weed Stay in Your Hair Follicle?

woman with dark curly hair

Drug tests come in various forms typically using blood, urine, and saliva. However, some drug tests use hair. If you’ve been ordered a hair drug test, you’re probably wondering how long weed stays in your hair follicle. The answer may be good or bad based on your situation. 

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How Long Does Weed Stay in Hair Follicles? 

Weed can stay in your hair follicle for up to 90 days or three months. Out of all available tests, the hair test can pick up on weed use after the longest period since the last use. For example, a urine test can only you used your bong during the previous three days. 

However, these time periods aren’t the same for everybody. You may process weed differently from someone else. For example, if you use weed every day, weed will show up for a more extended time in tests in contrast to someone who uses it occasionally. 

So, you may be wondering how weed gets in your hair in the first place. Healthline says, “cannabinoids reach the hair follicles via small blood vessels, as well as from sebum and sweat surrounding the hair shaft.” 

As Healthline explains it, since hair grows around 0.5 inches, 1.5 inches of hair should be able to show weed use over the last three months. 

However, the test cannot show exactly when weed was used. Healthline says, “hair growth rates vary from person to person, this test can’t accurately determine when in the 90 days drugs were used.”

How do Hair Drug Tests Work?

Hair tests are pretty simple. According to Healthline, 100-120 hairs are collected for testing. Testers can collect the hairs from various places, so you don’t have a ball spot. Don’t worry; nothing you do to your hair beforehand can alter the results. Therefore, you can wash, style, and use your regular hair products.

When the hair reaches the lab, Alere Toxicology, an enzyme-linked immunosorbent assay (ELISA) test, is conducted. After the ELISA test, the lab technician will do a confirmatory test.  

The confirmatory test is either Gas Chromatography/ Mass Spectrometry (GC/MS) or Gas Chromatography – Tandem Mass Spectrometry (GC-MS-MS). These confirmatory tests are typically done if the ELISA test is negative. 

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According to Medical News Today, confirmatory tests serve the purpose of reducing false positives. 

Sometimes, the hair test will come back inconclusive. Medical News Today says that means something went wrong during testing or the hair sample was contaminated. An inconclusive result typically means you’ll have to resubmit a hair sample. 

Are Hair Drug Tests Accurate?

That’s debatable. Medical News Today says, “Although hair samples undergo a two-step testing process, they are not 100 percent accurate.”

Certain factors could influence the concentration of the drug in the hair. For example, Medical News Today says that having dark-colored hair could affect the test. That’s because some substances bind more readily to melanin. 

In addition to that, the amount consumed also plays a factor. That means light users may end up with a negative test, while most chronic or more frequent users are more likely to test positive.

In a 2016 study, the hair test positively identified marijuana use in 77% of heavy users in contrast to 39% of light users. 

In another study, the hair test could not identify all self-reported marijuana users. The study said, “sensitivity of hair testing relative to self-report was low, identifying only 52.3% (127/243) of self-disclosed marijuana users.” The study also revealed that many users who self-reported but got a negative test were low-frequency users. 

So the bottom line is, yes, hair tests can be accurate, but it’s more likely to show a negative result for low-frequency users. On the other hand, it’s more likely to show a positive result for users with dark hair and those considered heavy users. Other factors we didn’t get into include how much a person sweats. 

What Happens If I’m Bald?

If you’re bald, you may still be able to do a hair drug test. According to Healthline, drug testers may use body hair for the test. 

Medical News Today got a little more specific and revealed that drug testers might collect hair from your face or armpit. However, the hair has to be between 0.5 to 1.5 inches. 


So, how long does weed stay in your hair follicle? Generally, 90 days or three months. While the test is accurate in some ways, it tends to provide a negative result for low-frequency users. Of course, nothing is 100% accurate, and several factors can influence the likelihood of a positive test. 


About Trevann

Trevann is Stoner Rotation’s Jamaica-based lead writer for the Science section of our cannabis blog. She graduated with honors receiving her Bachelor of Science degree in Molecular Biology from the University of West Indies, Mona. For the last three years, she has covered some of the biggest questions around cannabis and health underpinned with research from supporting studies, medical journals and scholarly articles. Got something on your mind? You can reach her at [email protected].