Hair follicle testing detects alcohol use over an extended period. It is increasingly employed in legal proceedings, child custody cases, and employment screenings, providing insights into an individual’s consumption history. This article explores its scientific principles, detection window, influencing factors, and result interpretation.
The Science Behind Hair Alcohol Testing
When alcohol is consumed, the body metabolizes it, producing metabolites. These metabolites, primarily Ethyl Glucuronide (EtG) and Fatty Acid Ethyl Esters (FAEEs), are incorporated into the hair structure. EtG is water-soluble and deposited into hair via sweat glands after liver formation. FAEEs are fat-soluble, entering hair primarily from the bloodstream and sebum, an oily substance from scalp glands.
As hair grows, these alcohol biomarkers become trapped within the hair shaft, providing a record of alcohol consumption over time. Laboratories analyze these samples to identify and measure EtG and FAEE concentrations.
Understanding the Alcohol Detection Window
Hair follicle tests for alcohol typically cover a detection window of up to 90 days. This timeframe is based on average scalp hair growth of about 1 to 1.5 centimeters (0.5 inches) per month. To cover 90 days, a hair sample of about 3.8 to 4.5 centimeters (1.5 inches) is collected from the scalp, often from the back of the head.
Hair alcohol tests detect patterns of chronic heavy alcohol use rather than isolated instances of consumption. It takes 7 to 10 days for alcohol metabolites to incorporate into the hair shaft and become detectable. Therefore, recent alcohol use within the past week may not be reflected in test results.
What Can Influence Test Outcomes
Several factors can influence hair alcohol test results. Individual hair growth rates vary, meaning the 90-day window is an average and can differ by person. Hair treatments, such as bleaching, dyeing, perming, and straightening, can also affect alcohol marker concentration.
Bleaching and perming can significantly decrease EtG levels due to chemical degradation and leaching. While FAEEs are more resistant, alcohol-containing hair products like hairsprays or gels can increase FAEE levels, potentially causing false positives. Laboratories typically account for these possibilities during interpretation.
Interpreting Hair Follicle Test Results
Interpreting hair follicle test results involves analyzing EtG and FAEE levels to distinguish ingested alcohol from external contamination. Laboratories often use cut-off values to categorize consumption levels. For instance, an EtG level below 7 picograms per milligram (pg/mg) may suggest abstinence, while levels above 30 pg/mg can indicate chronic excessive alcohol use.
EtG is a more reliable indicator of ingested alcohol, formed in the liver and transported to hair via sweat, making it less susceptible to external contamination. Conversely, FAEE levels can be influenced by external exposure. Therefore, both markers are analyzed together for comprehensive assessment, minimizing false positives from external sources.