When you think of testing for alcohol consumption, one device immediately comes to mind. You know it best as the breathalyzer, a common feature of roadside field sobriety tests. Through a process that converts residual ethanol on one’s breath to acetic acid, law enforcement can estimate the test subject’s blood alcohol content, with a particular eye toward the .08 BAC that serves as the legal limit in most states.

It’s a handy device, but one that is limited in scope. A breathalyzer can only measure alcohol consumption within a short time frame—roughly the last 12 hours. And testing for alcohol consumption goes far beyond the side of the road. The court may require people who are embattled in child-custody proceedings or enrolled in substance abuse programs to submit to tests that measure alcohol consumption within timeframes that stretch well beyond what breath, blood, or urine can accurately report. For this, courts prefer a hair follicle test, which offers results from the last 90 days. Multi-panel hair tests can detect 5-17 drugs, but alcohol is not among them. So how do hair follicle tests detect alcohol consumption? We’ll take a closer look.

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What’s “EtG”?

The process begins in the liver. Ethanol, which we refer to in common parlance as “alcohol,” is a complex molecule of hydrogen, carbon, and oxygen that the liver breaks down. As the liver metabolizes ethanol, a substance known as glucuronic acid aids in the process, where it creates a metabolite, or byproduct, called ethyl glucuronide, or EtG. As the body excretes these metabolites through sweat, hair absorbs them, where they can remain for months.

Testing Procedure

A hair follicle test takes 90-120 hairs for sampling—usually from the head, but if that is not an option, body hair is a viable alternative. A laboratory will assess the sample for the presence of EtG. While certain events can cause false positives, such as the use of mouthwash or hair products that include ethanol, these are unlikely, and a hair test is indeed a reliable means of testing for recent alcohol consumption. A hair follicle test can detect the metabolization of ethanol within the last 90 days.

In Closing

The most important thing to know about how hair follicle tests detect alcohol is that they’re hard to beat. Washing your hair or taking a dip in the pool on the day of your test is not enough to remove traces of EtG from your hair. Shaving your head to eliminate hair samples could only lead to more invasive sampling or forfeiture of the test. Indeed, the only way to pass an EtG hair follicle test is to do what you were supposed to do: abstain.