All substances that flow though the body are taken into the hair follicle. For this reason, hair tests can detect the presence of drugs for a much longer period of time (90 to 120 days is typical) than other types of substance abuse testing. The period of time that can be tested is dependent on the length of the hair- hair typically grows about ½ inch per month.
The collection consists of a small amount of head hair which is cut off at the scalp. The laboratory needs about 20-30 hair strands (about the width of a shoelace tip) and the sample can usually be collected so that the sample site is not visible.
Hair testing has proven to be an accurate and legally defensible method of drug testing and results are not affected by bleaching or coloring of the hair. Hair follicle testing is not yet approved for D.O.T. drug testing programs, although it is under consideration.
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