Residual mouth alcohol is a common defense to a DUI charge. The defense is premised on the concept of falsely high readings by DUI breath test devices. This happens when the breathalyzer picks up traces of alcohol that remain in the mouth, rather than in the deep lung tissue.
This alcohol will be detected by a DUI breath test, even though it has not yet been absorbed into the bloodstream. This can cause the DUI breath testing device to report a falsely high blood alcohol concentration (“BAC”).1
As a result, an innocent person might be charged with a crime such as:
- Driving under the influence, Vehicle Code 23152(a),
- Driving with a BAC of .08% or higher, Vehicle Code 23152(b), or
- Underage DUI (BAC of .05% or higher), Vehicle Code 23140.
Below our California DUI defense lawyers discuss:
- 1. What is “residual mouth alcohol”?
- 2. How does it lead to falsely elevated BAC results
- 3. Is it possible for someone who did not drink to test positive on a DUI breath test?
- 4. What is the 15-minute observation period for a DUI breath test?
- 5. How can mouth alcohol serve as a DUI defense?
- 6. The prosecution claims that mouth alcohol is not a valid legal defense. Is this true?
1. What is “residual mouth alcohol”?
“Mouth alcohol” consists of traces of alcohol that remain in the mucosal linings of the mouth. It is created whenever someone consumes (or regurgitates) anything with alcohol in it. Common sources of it include:
- Beer, wine, and liquor,
- Medical conditions like gastroesophageal reflux disease (GERD), acid reflux and heartburn,2
- Certain medicines such as Nyquil and some cough syrups,
- Chewing tobacco,
- Certain mouthwashes or breath sprays such as Listerine, and
- Dental work, such as dentures or retainers, that trap (and release) consumed food and liquid.
2. How does it lead to falsely elevated BAC results
When someone consumes anything containing alcohol -- even a small amount of alcohol -- some of it remains in the mucosal linings of the mouth. It dissipates quickly fairly quickly—typically about ten minutes after consumption.3
But it takes 30 minutes or more on average for this alcohol to enter the bloodstream. So immediately after consumption, it is present in the driver’s mouth but has not yet raised the drinker’s BAC level.
How mouth alcohol “tricks” a breath testing machine
Breath testing devices are meant to measure alveolar air (deep lung air).4 The “alveoli” are air sacs located deep within the lungs. They are surrounded by capillaries, blood vessels no more than 1/1000th of a millimeter thick.
Capillaries are so thin they allow gases to pass from the lungs into the bloodstream and vice versa. This includes alcohol vapor. So, a portion of any alcohol in the bloodstream can cross into the lungs.
When a person blows into a breath testing device, some of this vapor mixes with the exhaled air. The DUI breath testing machine measures this alcohol and mathematically converts the measurement into a roughly equivalent BAC reading (blood alcohol content).5
Unfortunately, breath testing machines cannot always distinguish “mouth air” from “alveolar” air.6
So if there is alcohol in the mouth, it will get mixed into the sample. This artificially raises the person’s BAC measurement, possibly above the legal limit. Anything at 0.08% or higher is illegal.
3. Is it possible for someone who did not drink to test positive on a DUI breath test?
Yes. Anything that contains alcohol can leave residual traces in the mouth. This can lead to a “positive” DUI breath test.
Products besides alcoholic beverages that often contain alcohol include cold medicines, chewing tobacco, mouthwashes and breath spray.
And in rare cases, elevated BAC can also result from medical conditions such as GERD and acid reflux. This is most likely to occur shortly after the alcohol is consumed.7
Any of these factors can raise a driver’s BAC into the “danger zone” for criminal charges.
4. What is the 15-minute observation period for a DUI breath test?
California law requires law enforcement officers to observe a DUI case subject for 15 continuous minutes before beginning an “evidentiary” (post-arrest) DUI breath test (a.k.a. chemical test).8 (This requirement does not apply to a preliminary alcohol screening (“PAS”) breath test that is given on a handheld “breathalyzer.”)
This 15-minute observation period is mandated by Title 17 of the California Code of Regulations (“CCR”). 17 CCR sets forth procedures police officers must follow during California DUI blood tests, breath sample tests and urine tests.9
The rationale behind the 15-minute observation period for a DUI breath test
Mouth alcohol generally dissipates within 15 minutes, as long as no other alcohol is introduced into the mouth. So by observing a driver continuously for 15 minutes, an officer can make sure the driver does not:
- Use breath spray,
- Put anything in his/her mouth,
- Burp (burping causes some reflux),
- Regurgitate, or
- Vomit (which could bring alcohol from the stomach into the mouth).
But as Pasadena DUI defense attorney John Murray10 explains:
“Law officers frequently fail to honor the 15-minute observation requirement. Many of them wait for 15 minutes before starting the test, but use the time to complete paperwork or check their phones. And even diligent officers can miss a burp or regurgitation that could cause false breath test results.”
5. How can mouth alcohol serve as a DUI defense?
Experienced California drunk driving lawyers can assert a mouth alcohol defense when:
- An officer did not wait a full 15 minutes before beginning a DUI breath test,
- The officer waited 15 minutes but did not observe the driver continuously during that time, or
- There is evidence that there was another possible source of mouth alcohol (such as alcohol regurgitated due to GERD or other digestive problems).
6. The prosecution claims that mouth alcohol is not a valid legal defense. Is this true?
No. While mouth alcohol is not always the most applicable of California DUI defenses, it is still a valid one. Prosecutors will point to studies that show that mouth alcohol does not contaminate a properly done DUI breath case.
But DUI breath tests are often not done properly. And the burden is on the prosecution to establish guilt beyond a reasonable doubt.
An experienced DUI defense attorney and, if needed, an expert witness can often find holes in police procedure. This is often enough to get a favorable result such as:
Charged with a California DUI? Call us for help…
If you or someone you care about was charged with driving under the influence, we invite you to contact our DUI attorneys for a free consultation.
We have local offices in Los Angeles, the San Fernando Valley, Pasadena, Long Beach, Orange County, Ventura, San Bernardino, Rancho Cucamonga, Riverside, San Diego, Sacramento, Oakland, San Francisco, San Jose and throughout California.
- See C.D. Simpson, “Effects of Mouth Alcohol on Breath Alcohol Results,” Western Michigan University, Feb 25, 2016.
- See, e.g., 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,”(“Extremely high BACs often indicate the presence of mouth alcohol (rather than alcohol absorbed into the drinker’s system)”), J Stud Alcohol Drugs. 2008 Jul; 69(4): 539–549.
- See, K. Sterling, “The rate of dissipation of mouth alcohol in alcohol positive subjects,” J Forensic Sci. 2012 (“The average time for subjects to reach their unbiased BrAC was 9.35 min…”).
- 17 California Code of Regulation (“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 for the purpose of measuring its alcohol concentration.”
- 17 CCR 1220.4(f): “A breath alcohol concentration shall be expressed as the number of grams of alcohol per 210 liters of breath.”
- Wigmore, endnote 3.
- See Kechagias, Jönsson, Franzén, Andersson, and Jones, “Reliability of breath-alcohol analysis in individuals with gastroesophageal reflux disease,” J Forensic Sci. 1999 Jul;44(4):814-8.
- 17 CCR 1221.2(a)(3)(A)(iv).
- 17 CCR 1215 and subsequent sections.
- Pasadena DUI defense attorney John Murray is a leading expert in California DUI defense, including the use of mouth alcohol as a defense against DUI charges. He has extensive experience both in the court systems of Los Angeles County and Ventura County and in California DMV hearings.