When you are consuming marijuana, it will be taking 5 days to turn up in your blood and traces of marijuana can be detected all through for quite a few months. If you are wondering why the traces of drugs in the hair is visible, well it is because when Marijuana is ingested it blends well with the blood and circulates all around the body.
Since it remains in the blood stream so it can be detected through blood, urine and saliva. Hair shafts get contaminated with the drugs as drug metabolites are deposited onto the hair follicle. Approximately .5 inches is the average growth rate for the hair and when the hair is tested at labs for toxin metabolites confined in the shaft core, it becomes easier to have it tested. If you are wondering, of how to pass a hair follicle test whether it is possible to wash off the chemical from the hair, well, for your information Drug metabolites are chemicals which are stably stored in the hair and is also traceable in your hair shaft core, so simply with regular shampoo it cannot be washed off. You cannot scrub it off nor you can bleach it out. Normal, regular shampoos and cleansers are not having such potency to ward off traces of drugs.
However there are medicated, hair detoxification shampoos which are capable of removing the traces of drugs and metabolites detectable at the hair follicle. However these shampoos are available easily at online stores. All you have to know about them and purchase the suitable one. Maximum labs claim 99% accuracy but then again these tests are spoiled with flaws and so they can be escaped using varying measures. Bleaching the hair or coloring the same detoxify hair from drug residues.