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Why Mouth Alcohol Can Cause a Falsely Elevated Breath Alcohol Reading on the Breath Machine

Written by: George Fredrick Mueller

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However, alcohol may have come from the mouth, throat or stomach for a number of reasons.

To help guard against mouth-alcohol contamination, certified breath test operators are trained to carefully observe a test subject for at least 15-20 minutes before administering the test. The problem with mouth alcohol being analyzed by the breathalyzer is that it was not absorbed through the stomach and intestines and passed through the blood to the lungs. In other words, the machine's computer is mistakenly applying the "partition ratio" and multiplying the result. Consequently, a very tiny amount of alcohol from the mouth, throat or stomach can have a significant impact on the breath alcohol reading. Other than recent drinking, the most common source of mouth alcohol is from belching or burping. This causes the liquids and/or gases from the stomach—including any alcohol—to rise up into the soft tissue of the esophagus and oral cavity, where it will stay until it has dissipated. The American Medical Association agrees in its Manual for Chemical Tests for Intoxication.

Burp, Belch, Regurgitation of Gas, Acid reflux, Mouthwash, Breath Freshener, French Kissing a Drunk Person all can create mouth alcohol.

Police officers are supposed to keep a DUI suspect under observation for at least 15 minutes prior to administering a breath test. Instruments such as the Intoxilyzer 5000 also feature a "slope" parameter. This parameter detects any decrease in alcohol concentration of .006 g per 210L of breath in 6/10th's of a second, a condition indicative of residual mouth alcohol, and will result in an "invalid sample" warning to the operator, notifying the operator of the presence of the residual mouth alcohol. PBT's, however, feature no such safeguard. Acid reflux, or gastroesophageal reflux disease, can greatly exacerbate the mouth alcohol problem. The stomach is normally separated from the throat by a valve, but when this valve becomes herniated, there is nothing to stop the liquid contents in the stomach from rising and permeating the esophagus and mouth. The contents—including any alcohol—are then later exhaled into the breathalyzer. Mouth alcohol can also be created in dentures.

Additional Resources

The mucous lining of the mouth cavity and nasal passages stores alcohol for some time after a person consumes alcohol. Normal body processes eliminate residual mouth alcohol within 15 minutes. Therefore, observe a subject for at least 15 minutes before performing a test. During the observation time, the subject may not eat, drink, or introduce any substance into his mouth. Furthermore, if the subject regurgitates, note the time and delay starting a breath test for at least 15 minutes.
[CMI, Inc., Basic Maintenance and Repair of the Intoxilyzer Breath Analysis Instrument, 10/1/84, p. 44.]

Breath Test Defenses

The Significant 15 minute Continuous Observation of a Subject Prior to a Breath Test