Hair follicle testing analyzes hair strands to identify specific markers of past alcohol consumption over an extended period. Understanding its mechanisms and limitations provides insight into its application.
How Alcohol Reaches Your Hair
When alcohol is consumed, the body processes it, producing specific byproducts called metabolites. Two primary metabolites detected in hair are ethyl glucuronide (EtG) and fatty acid ethyl esters (FAEEs).
EtG forms in the liver and is subsequently deposited into hair primarily through sweat. FAEEs are formed when alcohol reacts with fatty acids in the body. These markers become incorporated into the hair primarily through sebum, the oily substance produced by glands in the skin, and through diffusion from the bloodstream.
Both EtG and FAEEs are considered direct markers of alcohol consumption. These markers begin to appear in hair approximately 7 to 10 days after alcohol intake, as the hair grows out from the scalp.
Standard Detection Period
Hair follicle tests typically provide a detection window of up to 90 days, or approximately three months. This timeframe is based on the average rate of human head hair growth, which is about 0.5 inches (1.25 to 1.3 centimeters) per month.
For testing, laboratories collect a hair sample of about 1.5 inches (3 to 4 centimeters) closest to the scalp. Since hair grows continuously, the segment closest to the scalp reflects the most recent consumption within this window, while further segments indicate earlier use.
While 90 days is standard, longer hair samples can extend the detection period up to six months or even a year. Hair tests cannot detect alcohol consumption within the last 5 to 7 days, as metabolites need time to incorporate into the growing hair shaft.
Factors Affecting Detection
Several variables can influence the results of a hair alcohol test. Individual hair growth rates vary depending on factors such as age, genetics, and sex, which can slightly alter the precise detection window for each person.
The quantity and frequency of alcohol consumed also play a role; tests are more effective at detecting chronic heavy alcohol use than isolated or infrequent instances of drinking.
Hair treatments like bleaching, dyeing, perming, or straightening can impact the concentration of alcohol markers found in hair. These chemical processes can reduce levels of EtG, which is water-soluble.
While FAEEs are more resistant to such treatments, their levels can be influenced by alcohol-containing hair products like sprays or gels, potentially leading to elevated readings.
Understanding Test Reliability
Hair follicle tests are considered a reliable method for identifying patterns of chronic heavy alcohol consumption. Hair testing provides a historical overview of consumption rather than indicating current intoxication or impairment at a specific moment.
False results are possible, though rare for EtG markers. False positives for FAEEs can occur due to external contamination from alcohol-containing hair products.
Conversely, false negatives might arise from very low consumption levels, certain hair treatments that wash out markers, or if the test is conducted too soon after drinking. To enhance accuracy, many laboratories perform testing for both EtG and FAEEs, as a combined analysis offers a more comprehensive picture of alcohol exposure.