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DUI - MOUTH ALCOHOL DEFENSE

Residual mouth alcohol is a common defense against falsely high BAC results using breath testing devices. Normally, a breath testing device makes a BAC reading from the deep lung air. However, breathalyzers can pick up traces of alcohol that has not yet been absorbed in the body that was left in the mouth. When this happens, it can lead to falsely high BAC readings that is why the defense is called “residual mouth alcohol” defense.

To help give you a better understanding of residual mouth alcohol, our West Covina defense attorneys will discuss some important things to know about this defense in the following article.

1: What is Residual Mouth Alcohol?

Mouth alcohol is trace alcohol left on the mucosal lining of the mouth. This happens a person consumes or regurgitates anything with alcohol in it. Common sources of mouth alcohol are found in the ff:

  • Liquor and other alcoholic beverages
  • Medical conditions like acid reflux, heartburn, and GERD[1]
  • Certain medications like cough syrups
  • Chewing tobacco
  • Mouthwash and certain breath sprays
  • Dental work that can trap food and liquid (dentures, retainers, etc.)

2: Falsely High BAC results

When a person consumes something with alcohol, some trace of it is left on the mucosal lining of the mouth. It disperses quickly enough, roughly around 10 minutes after being consumed.[2]

Mouth alcohol can give misleading BAC results

As mentioned earlier, breath testing devices measure breath samples from the deep lung air (alveolar air).[3] Alveoli are small air sacs found in the deep portion of the lungs and it is surrounded by capillaries, very thin blood vessels that are no thicker than 1/1000th millimeter.

Because the capillaries are so thin, these allow gasses to pass through to the lungs from the bloodstream such as alcohol vapor. So, when a person consumes alcohol, this gets absorbed in the bloodstream and when the blood circulates in the system, it can pass through the lungs as explained above.

Because a breath testing device is used by blowing air through the mouth, any residual mouth alcohol can mix in with the air from the deep lung. The breath testing device cannot distinguish between mouth alcohol from alcohol found in the deep lung air. The breath testing device measures the alcohol it detects and converts this measurement into a close approximate of blood alcohol concentration or BAC. Because of this, the reading it provides does not accurately reflect the actual BAC in a person's bloodstream. The breath testing device will most likely show a result that is higher than the actual BAC in your system and it can provide a BAC reading higher than 0.08%.

3: Positive Reading on Breath Testing Device Even Without Drinking

If you are wondering if you can test positive on a breath test without drinking, then the answer is yes. As mentioned previously, mouth alcohol can come not only from alcoholic beverages like liquor, beer, or wine. It can also come from other products like mouthwash breath sprays, medication, chewing tobacco, etc.

In some cases, having a certain medical condition can elevate BAC results provided by a breath testing device. Acid reflux and GERD are notorious for giving falsely high BAC results with breath testing devices.

4: 15-Minute Observation Period

According to Title 17 of the California Code of Regulations,[4] police officers are required to observe a person for 15 straight minutes before post-arrest breath testing. This is to make sure that a person being tested does not ingest alcoholic beverages or other fluids, regurgitated, vomited, eaten, or smoked before providing a breath sample.

If the 15-minute wait period is not observed properly, an experienced California DUI defense attorney can mitigate or have a DUI charge dropped altogether.

Why 15 minutes?

The general idea behind the 15-minute observation period is that any mouth alcohol that could be present in a person’s mouth dissipates within 15 minutes so long as no other alcohol or alcohol source is introduced within those 15 minutes.

5: Mouth Alcohol as A DUI Defense

An experienced California DUI defense attorney can claim mouth alcohol defense if:

  • 15-minute observation was not observed properly.
  • The police officer waited 15 minutes before the breath test but did not continuously observe the driver during those 15 minutes.
  • There is presence of evidence of another possible source of alcohol (such as alcohol from regurgitation)

6: Prosecution: “Mouth alcohol not a valid legal defense”

If you are being charged with a DUI, most likely, the prosecution will claim that mouth alcohol is not a valid legal defense. The prosecution will most likely highlight studies that claim that mouth alcohol does not affect breath tests that were properly conducted. Is it true? Not at all. Because not all breath tests are conducted properly, and it is up to the prosecution to prove guilt beyond reasonable doubt.

While the defense of mouth alcohol is only applicable under certain circumstances, it is still a valid legal defense.

An experienced California DUI defense attorney with the help of an expert witness can often find fault in police procedures. It is possible to have the charges reduced or even dropped altogether.

Mistakes Happen. A DUI Record, Losing Your License and Jail Don't Have To.

Mouth alcohol can lead to false BAC readings or falsely high BAC results. You will want to consult and secure the services of an experienced DUI defense attorney to assist you in navigating the complexities of fighting against a DUI charge because it can be extremely difficult to manage a DUI charge on your own. You will want to avoid a conviction at all costs because nobody wants to be convicted for inaccurate results or something that is attributed to their medical condition. A DUI conviction can have severe effects on your life. If you need assistance with a DUI charge, do not hesitate to contact us at 626-827-7222 to schedule your consultation with one of our experienced attorneys at no cost. Although we are fielding inquiries from a lot of people in similar situations, we will do our best to put you in contact with an experienced lawyer from our firm.


[1] Johnson, Voas, Kelley-Baker, Furr-Holden, “The Consequences of Providing Drinkers with Blood Alcohol Concentration Information on Assessments of Alcohol Impairment and Drunk-Driving Risk”, J Stud Alcohol Drugs. 2008 Jul; 69(4): 539–549

[2] K. Sterling, “The rate of dissipation of mouth alcohol in alcohol positive subjects,” J Forensic Sci. 2012

[3] CCR 1215 (r): "'Sample' or 'Specimen' means a representative portion of blood, urine, tissue, an artificially constituted material, or a portion of expired breath which is essentially alveolar in composition obtained to measure its alcohol concentration."

[4] 17 CCR 1221.2(a)(3)(A)(iv)

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