Hair follicle testing detects various substances within a person’s system by analyzing a small hair sample. This method provides a detection window for past substance use, offering a distinct advantage over other testing methods due to its longer historical record of substance exposure.
How Hair Follicle Tests Work
When substances are consumed, they enter the bloodstream and circulate throughout the body. These substances, along with their metabolic byproducts, become incorporated into the hair shaft as it forms and grows from the follicle. The hair acts as a chronological record, embedding these compounds within its structure.
For testing, a small hair sample is collected by cutting strands from the crown of the head, as close to the scalp as possible. If head hair is unavailable, body hair can be used. In the laboratory, hair is thoroughly washed to eliminate external contaminants. The washed hair is then dissolved, and embedded substances are extracted. These compounds are identified and measured using analytical techniques, typically involving an initial immunoassay screening followed by confirmatory tests like gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS).
Substances Detected and Their Detection Windows
Hair follicle tests detect a range of substances and their metabolites. Common categories include cannabis, cocaine, opioids, amphetamines, and phencyclidine (PCP). Specific examples within these groups include methamphetamine, MDMA (ecstasy), heroin, codeine, and morphine.
The advantage of hair testing is its extended detection window, typically covering up to 90 days for scalp hair. This window is based on the average growth rate of scalp hair, which is approximately one-half inch per month, meaning a standard 1.5-inch hair sample reflects about three months of history. It usually takes about 7 to 10 days for substances to become detectable in hair after use, as the hair needs to grow out from the scalp. While scalp hair provides a consistent 90-day window, body hair can extend the detection period to up to 12 months, though with less precision regarding the exact timeframe of use.
Factors Influencing Test Results
Several factors can influence the outcome and interpretation of hair follicle test results. External contamination from environmental exposure, such as passive exposure to secondhand smoke containing drug residues, can affect findings. Reputable laboratories employ rigorous washing procedures to minimize the impact of such external factors before analysis.
Hair treatments, including bleaching, dyeing, perming, or chemical straightening, can also alter the concentration of drug metabolites within the hair shaft. The chemicals used in these treatments can damage the hair’s structure, potentially leading to a reduction in the detected drug content, sometimes by as much as 40-60% for certain substances following bleaching. Laboratories often visually inspect samples for evidence of cosmetic treatments and account for these factors in their interpretive reports.
Hair color can also play a role, as some drugs tend to bind more readily to melanin, the pigment found in darker hair. Individual variations in hair growth rates and the amount of sweat or sebum produced can further influence how drugs are incorporated and retained in the hair.
Common Uses and Interpretation
Hair follicle testing is utilized in various contexts where a historical record of substance use is relevant. It is frequently employed in pre-employment screening and random drug testing programs within workplaces. The tests are also applied in legal and forensic settings, such as probation and parole monitoring, child protection cases, and post-mortem investigations.
A positive result from a hair follicle test indicates that the detected substance was present in the individual’s system within the established detection window, typically the past 90 days. These tests generally do not provide information about the exact date of use, the frequency of use, or the quantity consumed. A hair test cannot determine current impairment or intoxication. The results are usually interpreted by qualified professionals who consider all available contextual information to provide a comprehensive assessment.