Hair follicle testing is a method for detecting substance use over an extended period. It offers a longer detection window than blood or urine analyses. Its non-invasive nature and ability to provide a historical record of substance exposure make it useful in employment screening, legal proceedings, and monitoring abstinence.
What Hair Follicle Tests Identify
Hair follicle tests do not directly detect alcohol. Instead, they identify specific biomarkers produced when alcohol is consumed. The primary biomarkers are Ethyl Glucuronide (EtG) and Fatty Acid Ethyl Esters (FAEEs), including Ethyl Sulfate (EtS). When alcohol is broken down in the liver, EtG and FAEEs form as byproducts. These metabolites circulate in the bloodstream and incorporate into the hair shaft as it grows.
EtG is water-soluble and deposits into hair primarily through sweat glands. FAEEs are fat-soluble and incorporate via blood circulation and sebaceous glands. The presence of these markers in hair indicates alcohol consumption, providing a historical record rather than current impairment.
Detection Window for Alcohol
Hair follicle tests offer a longer detection window for alcohol consumption than other methods. For a standard 1.5-inch (3.9 cm) hair sample, alcohol metabolites can be detected for up to 90 days. This extended timeframe is due to the consistent hair growth rate, averaging about 0.5 inches (1 cm) per month. As hair grows, alcohol metabolites are “locked” into the hair shaft, creating a chronological record.
Longer hair samples can provide insights into alcohol use over an even more extended history, sometimes up to six months or more. However, it takes approximately 7 to 10 days for alcohol metabolites to incorporate into the hair strand and become detectable. This means recent alcohol use might not immediately register on a hair test.
Factors Influencing Test Outcomes
Several variables influence hair follicle alcohol test results. The primary factor is the pattern of alcohol consumption; these tests are more reliable for detecting chronic, excessive alcohol use rather than isolated or infrequent drinking. Consistent or heavy alcohol use significantly increases detection likelihood. Low levels of daily consumption may not produce measurable EtG levels in hair that cross cut-off thresholds.
External factors and hair treatments also impact test outcomes. Cosmetic hair treatments like bleaching, dyeing, perming, and excessive washing can reduce water-soluble EtG levels. Conversely, alcohol-containing hair products (e.g., hairsprays, gels) can increase fat-soluble FAEEs, potentially leading to false positive results for this marker. Laboratories consider these variables and analyze both EtG and FAEEs. Hair color and texture play a role, as alcohol metabolites can attach to melanin, affecting concentrations based on pigmentation.
Interpreting a Positive Test Result
A positive hair follicle alcohol test for EtG and FAEEs indicates chronic excessive alcohol consumption over the detection period. Laboratories use established cut-off levels to distinguish between incidental exposure, moderate social drinking, and chronic excessive use. For instance, an EtG concentration of less than 7 picograms per milligram (pg/mg) in hair aligns with self-reported abstinence, while 30 pg/mg or more suggests chronic excessive alcohol consumption. Levels between these thresholds (7-30 pg/mg) may indicate regular, but not necessarily excessive, alcohol consumption.
These tests assess a history of alcohol use patterns, not current intoxication or a single instance of drinking. While a positive result signifies alcohol metabolites, interpretation considers concentration levels and typical drinking patterns. A positive test for alcohol metabolites in hair primarily serves as an indicator of past, sustained alcohol intake.