Since hair growth is fed by the bloodstream, the ingestion of drugs of abuse is revealed by analyzing a small sample of hair. Testing method measures the drug molecules embedded inside the hair shaft, eliminating external contamination as a source of a positive test result.
It is becoming increasingly common for employers and the courts to ask for a Hair Drug Test. Testing for illegal substances in hair gives you a greater time frame of detection than urine, blood and saliva. In fact, you can often detect drugs in hair for several months – if not years, if the hair is long enough. Normally 90 days is all that is requested. However, some States require 120 days.