Alcohol Breath Tests and Mouth Alcohol: Why You Should Avoid Breath Mints When Testing

A common cause of falsely high readings from alcohol breath tests is "mouth alcohol". A breath analyzer is supposed to measure the amount of alcohol in the air in a person’s lungs, which correlates to the amount of alcohol in the blood, but unless the device contains a slope detector it is unable to distinguish air from the lungs and air from the mouth. Unless enough time has passed to allow alcohol to dissipate, air from the mouth contains a higher level of alcohol than air from the lungs (therefore air in the bloodstream) causing a breath analysis machine to register a falsely high BAC.

The most common source of mouth alcohol is from eructation (belching). When this happens, any alcohol or alcohol vapor in the stomach rises up into the soft tissue of the esophagus and mouth, where it stays until dissipated by respiration and saliva. It takes about 15 minutes for this dissipation to occur, and, for this reason, police officers are often required to keep a DUI suspect under observation for at least 15 minutes prior to administering alcohol breath tests.

Other sources of mouth alcohol include dentures, which can trap alcohol for longer than 15 to 20 minutes, periodontal disease, breath fresheners, and acid reflux. Acid reflux can be a particular problem because when alcohol or alcohol vapor enters the mouth this way, it has not yet been absorbed into the blood and should not be read as alcohol from the lungs.

Some alcohol breath analyzers have what is called a slope detector, which is a device intended to detect and correct for the presence of mouth alcohol. Alcohol content in a single breath can be graphed, and mouth alcohol graphs differently than alcohol from the lungs. Alcohol from the lungs increases, or slopes upward, then plateaus. Mouth alcohol increases and then sharply decreases, producing a graph with an up slope, a peak and a down slope. A slope detector aborts the breath analysis if it observes a down slope.

Sometimes, however, slope detectors are unreliable. When there is alcohol in the mouth and in the blood, the up slope from lung alcohol will add to the down slope caused by mouth alcohol to produce a level curve or a flat line resembling the plateau in a lung alcohol graph. So, a slope detector may prevent someone who is sober but has alcohol in the mouth from registering a BAC, but it may not prevent someone who has some alcohol in the blood from registering a false BAC.

Our breath alcohol testing machines advise people to wait 5 minutes before testing to avoid this problem. Following this simple guideline will make alcohol breath tests more accurate.