These are some tips that anyone who is taking a hair test should know. A cousin of mine works for Quest Diagnostics and literally handed me the business on hair testing. My cousin has been performing clinical testing on hair for 8 years now. She is licensed and a veteran in the business, so I trust her word, despite what you and I think we know, she does this every day.
http://www.marijuana.com/community/threads/what-you-need-to-know-about-hair-testing.286845/
How long does marijuana stay in your hair? It takes approximately 5 days for marijuana to show up in your hair it can continue to be detectable through a hair drug test for several months. The presence of Marijuana and other drugs in your hair can be understood by this basic principle.
https://www.theweedblog.com/how-to-pass-a-hair-follicle-drug-test-for-marijuana/
4 doctors agreed: Depends on use.: It depends on how often you use it. If you used it only once it can be detected by blood for 12-24 hours while it is detected in urine from 1-7 days. With regular use it can be detected in blood for 2-7 days and in urine anywhere from 1-100 days even if a heavy user. Age, height, weight, metabolism all are considered factors. ...Read more.
https://www.healthtap.com/topics/how-long-does-marijuana-stay-in-your-hair-follicles
The body can be cleansed naturally of toxins like marijuana in roughly 30 days. Once your blood and urine is clean your hair shaft core will become clean of marijuana as well and after roughly 3 months of hair growth or 1.5 inches your new collectible hair samples will be clean.
https://www.theweedblog.com/how-to-pass-a-hair-follicle-drug-test-for-marijuana/
The day you use drugs, any hair that grows after that for a certain time frame will contain chemicals from the drugs. If that hair stays on your head, six months later, it is possible that if that hair is used for a hair sample that it will be detected.
http://www.howlongdoesmarijuanastayinyoursystem.net/hair_drug_testing.html
Historical drug use can be measured based on the length of your hair sample from your scalp line but a specific timeline of usage is not possible. They cannot tell the difference between THC metabolites introduced two weeks ago from metabolites introduced two days ago.
https://www.theweedblog.com/how-to-pass-a-hair-follicle-drug-test-for-marijuana/
Best Answer: To fail a hair test, you need to smoke marijuana 3 different times. The typical testing time for chronic (daily) users is 90 days. Taking just a hit or 2 might cause a fail on a urine test within 48 hours but will never trigger a fail on a hair test. It is not possible for you to fail. Period.
https://answers.yahoo.com/question/index?qid=20100127140932AAdb1VP
Believe it or not, the chemicals will actually become part of your hair, and it would be interesting to see some research to see how drug use can affect your hair as well. Here is a list of why hair follicle tests are better for the tester: Chemicals become part of your hair and can be traced.
http://www.howlongdoesmarijuanastayinyoursystem.net/hair_drug_testing.html
With a urine test, using marijuana for example, it could only date back as much as 7-10 days (depending on your metabolism and the THC?s half life) for the casual user but with a hair follicle test, marijuana can be detected (if the hair is still there) from as far as three years prior if you used marijuana.
http://www.howlongdoesmarijuanastayinyoursystem.net/hair_drug_testing.html
The day your blood is free of THC is the day your hair will stop growing with THC in it. At this point she recommends cutting your hair...its the only 100% sure way to test negative...and that's only if you have the time to grow 1.5 centimeters back before the test.
http://www.marijuana.com/community/threads/what-you-need-to-know-about-hair-testing.286845/
how long does marijuana stay in your hair follicles
Marijuana stays for three years in your hair follicles. Marijuana stays three years in your hair follicles.