Most of the people who are going to hair follicle test. The first question came to mind how fast does the hair on my head grow. Usually, human head hair grows about 1/2 inch per month. That said, the history of drug use captured in a standard hair sample can vary by as much as one week either way, depending on hair type. Your ethnicity, hair thickness, and hair color will all impact how many days of history are detectable in the sample. Coarse and curly hair takes more time to grow. For this reason, more than 90 days of drug use may be locked inside a 1.5-inch sample of dark, curly hair. Fair, straight, thin hair grows faster than average. So, less than 90 days of history may be captured in a blonde hair sample. http://hairfollicledrugtest.info/hair-follicle-drug-testing-faq/