Hair drug testing detects past substance use by analyzing a small sample of hair. It examines hair strands for specific compounds, providing insights into an individual’s drug history over an extended period. Unlike other common methods, this testing approach offers a longer detection window.
How Drugs Enter Hair
When a substance is consumed, the body processes it, breaking it down into metabolites. Both the parent drug and its metabolites circulate throughout the bloodstream. Hair follicles, nourished by blood vessels, absorb these substances from the bloodstream as hair grows.
As the hair shaft forms, these drug compounds and their metabolites become encased within the hair’s structure. The hair acts like a timeline, recording the presence of these substances as it emerges from the scalp.
Once incorporated, drug metabolites remain stable within the hair, allowing for detection long after initial use. It takes about 5 to 10 days for drugs to appear in hair, as the hair needs to grow sufficiently above the scalp.
What Hair Tests Detect
Hair tests identify a range of illicit substances and misused prescription medications. These include cocaine, opioids, amphetamines, methamphetamine, ecstasy, marijuana, and phencyclidine (PCP). The tests look for both the parent drug and its metabolites, which are breakdown products indicating consumption.
A standard 1.5-inch head hair sample provides a detection window of approximately 90 days. This is due to head hair’s average growth rate of about half an inch per month. For body hair, which grows at a different rate, the detection window can extend up to 12 months.
This extended detection period distinguishes hair testing from methods like urine or oral fluid tests, which have much shorter detection windows. However, hair tests are not suitable for detecting very recent drug use, as substances require several days to be incorporated into the hair shaft.
Factors Affecting Hair Test Results
Several elements can influence hair drug test results. External contamination, where drug residues from the environment adhere to the hair surface, is a consideration. Laboratories employ specific washing procedures to remove such external contaminants before analysis to ensure that detected substances are from internal consumption.
Hair treatments, such as dyeing, bleaching, perming, or straightening, can also affect drug concentrations in hair. The chemicals used in these processes may damage the hair shaft, potentially altering the amount of drug or metabolite present. Hair color can also play a role, as certain drugs may bind more readily to melanin found in darker hair.
Individual differences in metabolism and hair growth rates can also impact test results. While average growth rates are used for detection windows, variations among individuals can slightly alter the precise timeframe represented by a hair sample.
The Hair Sample Collection Process
Collecting a hair sample for drug testing follows a standardized procedure to maintain integrity and accuracy. Hair is typically collected from the crown of the head, as close to the scalp as possible. If head hair is unavailable or too short, body hair from areas like the chest, underarm, or leg can be used.
A typical sample requires about 100 milligrams of hair, roughly 90 to 120 strands, or about the thickness of a pencil. For a 90-day detection period, approximately 1.5 inches of hair is needed. The collection process is often observed to prevent tampering and ensure the sample’s authenticity.
Once collected, the sample is securely packaged and sent to a laboratory with strict chain of custody documentation. This documentation tracks the sample from collection to analysis, ensuring its integrity for accurate results. In the lab, hair samples undergo processes like washing, pulverization, and extraction before analytical techniques such as gas chromatography-mass spectrometry (GC/MS) are used for precise identification and quantification of drugs and metabolites.