Hair screening or drug testing, works like any other method in which the test is designed to detect metabolites. Metabolites are the by-products of drugs that have passed through the human body and remain in the system for a specified period as described by the table released by the NIDA and SAMHSA that gives the timeframe by which a substance remains in the body. It would be very rare to find the exact drug that was ingested in its original form for any thing that passes through the human body is either broken down or transformed resulting in by-products which we normally excrete through our bowel or urine. If found in pure form, a substance may have been transferred or absorbed mechanically by the hair for it does not have any means to process any substance after the hair follicle leaves the growing zone or root. Hair screening is a good method for detection for the hair follicle itself is just similar to plastic where anything that is added stays embedded within it as long as the hair is intact. It can provide historical information on the type of drug and the frequency and doses as well which tends to make it a perfect tool by which to measure and determine drug use.

Hair screening for drugs uses a small sample of hair which can be from the head or body hair. It measures the amount of drugs and metabolite molecules present in the sample after it has passed through the human body. It can detect all five substances listed in the NIDA-5 category for mandatory drugs testing namely THC (marijuana, Cannabinoids), Cocaine (crack, cocaethelyne, benzoylecognine), Amphetamines (speed, methamphetamine), Opiates(Heroin, codeine, morphine, opium) and Phencyclidine (PCP). Which have been determined to be the most common abused substances in the US.

As it moves through the body it is then deposited on the hair follicles as it grows leaving a historical map and timeline due to the predictability of hair growth which is around ½ inch every month or 1.3 cm. The standard minimum amount of hair needed for screening with GC/MS is 40mg. of hair or approximately 50 to 70 strands at a length of 1.5 inches.

Contaminates or metabolites as they are caused can either be in the form of the drug itself of derivatives which have been processed by the human body. As an individual uses drugs, it enters the digestive tract or nasal membranes then travels through the blood stream to the various parts of the body. When these contaminants reach the scalp they become embedded or deposited in the core of hair follicles which tend to stay for as long as the hair is present.

Growing at a rate of a half inch every month, hair can store not only the substance but also shows the concentration and historical record of the substance that was abuses for months or even years. Some people try to defeat this by getting their head shaved but unbeknownst to them, any hair from the human body is capable of being tested for they all grow at the same rate. Standard screening procedures can determine usage for the past 90 days but can be extended to more than 180 days with more expensive screening procedures.

An individual hair is called a shaft and consists of three parts, the inner layer or medulla, the cortex and the cuticle. Hair consists mainly of dead keratin a hard proteins in the form of scales if looked at under a SEM (Scanning Electron Microscope). The ability of the hair follicle to hold information due to the depositing of these contaminants makes it ideal as a source of information on drug use and abuse. There is no known way to remove these substances from a hair follicle unless it is destroyed.

The sample is then cut into small pieces and soaked in a solution or solvent which dissolves the keratin leaving the metabolites in suspension ready for testing or screening. It is then separated through a centrifuge, and then tested in a manner similar to a urine test.

There are commercially available drug masking remedies as they claim that are categorized as surfactants that cover the hair follicles with an impenetrable layer of material thus making it impenetrable to the solvents used for the extraction of the specified contaminants. The first part of this product opens up the cuticles of the hair follicle and then a second product adds sealant to the spaces in between the hair. It is designed to retain the contents of the hair follicle by not allowing it to leach through the hair follicle and leaving itself in suspension in the extraction fluid. It takes on the presumption that if there is nothing to detect, there is nothing that would require further laboratory testing. If the said sample is re-tested in a laboratory, it may be possible to defeat this surfactant with the use of better equipment and more controlled environments. Laboratories are regulated by the NIDA and SAMHSA (Substance Abuse and Mental Health Services Administration) who sets the criteria and screening of these testing facilities to assure that they conform with federal legislation that sets the types and standards to be used is testing.

Hair samples as well as other samples for use in drugs testing follow strict accountability or Chain of Custody rules especially if these are for use in the court of law for it to be admissible. The chain of custody indicates the time, date, place and the name of the individual from whom the sample comes from and is updated and received by any person the specimen passes through. Upon receiving at the laboratory the safety seal is checked and if tampering is evident discarded as an adulterated sample. The chain of custody sheet contains spaces for the writing of the name of the individual who collected it, transported it and processed at the different authorized laboratories under the supervision SAMSHA and NIDA. Tampered safety seals are grounds for examination rejection most importantly if they are for application in Federal court cases or investigation.