Hair follicle testing offers a non-invasive way to examine long-term alcohol consumption patterns. Unlike blood or urine tests, which provide a snapshot of recent use, hair analysis can reveal evidence of alcohol use over several months. The method works by detecting specific compounds the body produces when processing alcohol, which become incorporated into the growing hair shaft.
Alcohol Biomarkers in Hair
The body processes ethyl alcohol (ethanol) into unique byproducts known as direct biomarkers, which the hair test identifies. The two primary biomarkers analyzed are Ethyl Glucuronide (EtG) and Fatty Acid Ethyl Esters (FAEEs). These substances are distinct from alcohol and are only produced following consumption.
EtG is a water-soluble metabolite formed in the liver and incorporated into the hair primarily through the bloodstream at the root. It can also be deposited onto the hair through sweat glands. Due to its water-soluble nature, EtG is more susceptible to being washed out or chemically degraded by external factors.
FAEEs are a group of fat-soluble compounds, including ethyl palmitate (EtPa), produced after alcohol is consumed. They are incorporated into the hair mainly through sebum, the oily substance secreted by the sebaceous glands on the scalp. Since FAEEs are fat-soluble, they are generally more resistant to chemical washing effects than EtG. Testing for both EtG and FAEEs provides a comprehensive picture of consumption history.
Standard Detection Window and Sample Analysis
The standard detection window for alcohol consumption is approximately 90 days (three months). This timeline is determined by the average growth rate of scalp hair, which is about 0.5 inches (1.5 centimeters) per month. To cover the full 90-day window, laboratories typically require a hair sample of about 1.5 inches, measured from the root closest to the scalp.
The collection process involves cutting a small bundle of hair as close to the scalp as possible. Biomarkers are trapped in the hair shaft as it grows, meaning the segment closest to the head represents the most recent period. The end of the 1.5-inch segment reflects consumption from about three months prior, allowing the test to document alcohol intake over the entire period.
How Usage Frequency Affects Detection
Hair follicle testing is primarily used to identify patterns of sustained, heavy alcohol consumption rather than isolated drinking events. The Society of Hair Testing (SoHT) establishes specific cutoff values to differentiate between occasional use and chronic excessive use. A concentration of EtG at or above 30 picograms per milligram (pg/mg) suggests chronic excessive alcohol consumption, defined as consuming 60 grams or more of pure ethanol daily over several months.
A single instance of light or moderate drinking is unlikely to meet this high cutoff threshold. However, a lower EtG cutoff of 5 pg/mg is used to suggest repeated alcohol consumption, distinguishing it from reported abstinence. The test measures the cumulative presence of biomarkers over time, making it a reliable measure of a sustained habit rather than recent, isolated use.
Factors Influencing Test Accuracy
Several variables can influence test accuracy and potentially shorten or lengthen the 90-day detection window. Cosmetic treatments, such as bleaching, dyeing, or perming, significantly affect biomarker concentration. Bleaching, in particular, can open the hair cuticle and degrade or wash out the water-soluble EtG marker, potentially leading to a false-negative result or underestimation of consumption.
While FAEEs are more resistant to chemical treatments, their levels can be artificially increased by using alcohol-containing hair products, such as hairsprays or gels, potentially leading to a false-positive reading. The individual’s hair growth rate is also a factor, as a faster or slower rate will shorten or extend the time represented by the standard 1.5-inch sample length. If head hair is unavailable, body hair can be used as an alternative, but interpretation is less precise due to the variable growth cycles of body hair.