Hair follicle testing for alcohol assesses an individual’s past alcohol consumption patterns by analyzing specific substances incorporated into the hair shaft. This method provides insights into historical alcohol use and offers a longer detection window than other tests, making it a valuable tool.
The Science of Detection
When alcohol is consumed, the body metabolizes it, producing specific byproducts that can be detected. Two primary biomarkers sought in hair follicle alcohol tests are Ethyl Glucuronide (EtG) and Fatty Acid Ethyl Esters (FAEEs).
EtG is a water-soluble metabolite formed almost exclusively in the liver when ethanol is present, and it is primarily deposited into hair through sweat glands. FAEEs are fat-soluble compounds formed in the body from ethanol reacting with fatty acids. These are incorporated into the hair primarily through sebum, an oily substance, and also via blood circulation.
As hair grows, these metabolites become trapped within the hair shaft’s protein structure, providing a record of alcohol consumption. The concentration of these markers in the hair generally correlates with the amount of alcohol consumed.
Detection Window and Influencing Factors
A hair follicle test typically provides a detection window of up to 90 days for scalp hair. This is based on the average scalp hair growth rate of approximately one-half inch to one centimeter per month, meaning a standard 1.5-inch sample reflects consumption over the preceding three months.
The detection window can be influenced by individual variations in hair growth rates, which can range from 0.5 cm to 2 cm per month. Factors such as genetics, race, age, health, and hormonal levels can affect how quickly hair grows. For individuals with slower hair growth, a 3 cm sample might cover a longer period, while faster growth rates could mean the same length covers a shorter timeframe. When scalp hair is unavailable, body hair (such as from the arm, back, chest, or armpit) can be used, extending the detection window to approximately four to twelve months, though body hair cannot be segmented for month-by-month analysis.
Interpreting Test Results
Interpreting hair follicle alcohol test results involves analyzing EtG and FAEE concentrations. A negative result suggests abstinence or very low alcohol consumption, while levels above certain cut-offs indicate alcohol use. For example, an EtG concentration of 30 picograms per milligram (pg/mg) or more in a 3 to 6 cm scalp hair segment suggests chronic excessive alcohol consumption.
The test primarily identifies patterns of chronic or excessive alcohol consumption, aiming to show sustained use over time rather than isolated drinking episodes. The Society of Hair Testing defines chronic excessive alcohol consumption as an average intake of 60 grams of pure ethanol per day over several months, roughly 7.5 units daily.
Limitations and Considerations
Hair follicle alcohol testing has limitations. It provides an overview of consumption over the detection period, but cannot determine the exact date or quantity of alcohol consumed. External contamination from alcohol-containing products like hair sprays can affect FAEE levels, potentially leading to false positives, though laboratories wash samples to minimize this. EtG is less susceptible to contamination.
Hair treatments like bleaching or dyeing can reduce EtG levels, potentially causing false negatives, while FAEE levels are more resistant. Darker hair may also retain higher concentrations of certain metabolites due to melanin binding. The test identifies alcohol metabolites, not active impairment, and does not reflect a person’s current state of intoxication.