A hair follicle drug test detects specific substances in an individual’s system over an extended period. This procedure is widely utilized in various contexts, including employment screening, legal proceedings, and situations requiring ongoing monitoring of substance use. It provides a historical overview of drug exposure, valuable for informed decisions.
How Hair Follicle Tests Work
Drugs and their metabolites enter the hair through the bloodstream, which nourishes the hair follicle. As hair grows, these substances become incorporated into the hair shaft, creating a historical record of drug use. Ingested drugs circulate in the bloodstream, reaching capillaries that supply hair follicles, then transfer into the hair matrix as hair grows.
To collect a sample, a small lock of hair, typically about 1.5 inches in length, is cut as close to the scalp as possible, usually from the back of the head. This sample is then sent to a laboratory for analysis. If head hair is unavailable, body hair can be used, though it may reflect a different detection window due to slower growth rates.
The Standard Detection Period
Hair follicle drug tests typically provide a detection window of up to 90 days, or approximately three months, for drug use. This timeframe is based on the average growth rate of head hair, which is approximately 0.5 inches per month. A standard 1.5-inch hair sample taken from the scalp can reflect drug use over the preceding three months.
It takes about 7 to 10 days from the time of drug exposure for detectable drug metabolites to appear in the hair shaft above the scalp. This means the test cannot detect very recent drug use, focusing instead on a longer history. This 90-day window applies to most commonly screened substances.
Influences on Detection Time
While the standard detection window is 90 days, several factors can influence the exact period drugs remain detectable in hair. Individual hair growth rates vary, with some people experiencing slightly faster or slower growth. This natural variation can alter the precise timeline a 1.5-inch sample represents.
The type of drug consumed and its metabolism within the body play a role, as different substances break down and incorporate into hair at varying rates. The amount and frequency of drug use also affect detection; chronic or heavy use may lead to higher concentrations of metabolites. While laboratories employ washing procedures, testing protocols differentiate between ingested drugs and surface contaminants.
Test Capabilities and Common Misconceptions
Hair follicle tests are capable of detecting a wide range of substances, including cannabis, cocaine, opioids, amphetamines, and phencyclidine (PCP). These tests are considered highly accurate and reliable, often involving a two-step process to confirm positive results and minimize false positives. The initial screening is followed by a confirmatory test, such as gas chromatography-mass spectrometry (GC/MS).
Several common misconceptions exist regarding hair follicle tests. Shaving one’s head does not bypass the test, as body hair can be collected as an alternative, and it may even provide a longer detection window. Special shampoos or hair treatments are ineffective at eliminating drug metabolites, as they are embedded within the hair shaft. These tests detect past drug use, not current impairment.