Mouth Alcohol Defense And The Breathalyzer In A DUI

DUI Defense Guide

In this post, I am going to explain a DUI defense known as the mouth alcohol defense.

When a person is pulled over for DUI by the police, they are usually required to take a breathalyzer test to determine whether their blood alcohol content is above the legal limit of 0.08% in California which is a violation under vc 23152(b).

Many times, breathalyzer reading may be inaccurate because the machine may malfunction or the police officer may cause an operator error or a reading has been affected by mouth alcohol. If a person has used a substance such as mouthwash before a breathalyzer test, the machine may give a reading that shows a high level of alcohol content in the person’s breath. This means that the machine will show that the person is legally intoxicated even though they may be completely sober.

Overview Of Mouth Alcohol As A DUI Defense

If you have been arrested for a DUI, you will be asked to give a sample of your breath on a breathalyzer in order to get a reading of your blood alcohol concentration level (BAC). In California and all other states, it is unlawful to operate a motor vehicle with a BAC of 0.08% or higher.

If your BAC is at this level, it creates a rebuttable presumption that you were under the influence at the time you were driving1. This places the burden on you and your defense attorney to show that the test results were inaccurate or gave a false high reading because of any number of factors.

Deep Lung Air

A breathalyzer is designed to capture a deep lung sample of your breath so as to presumably register an accurate reading of your BAC. Oxygen in our system passes from the lungs to our capillaries, or small blood vessels, but gases such as CO2 and alcohol that have not yet been metabolized also pass from the capillaries to our lungs.

When you exhale into the breathalyzer, these gases exit our lungs. The highest concentration of alcohol in our lungs is found in the alveoli, found deep inside the lungs, that appear as sacs that inflate and deflate as we breathe in and out. Because they are located above the capillaries, they represent the deep lung air that the breathalyzer is designed to capture.

Residual Mouth Alcohol

However, the breathalyzer will also pick up any residual mouth alcohol. This is alcohol from an alcoholic beverage or from some other source that can remain in your mouth or throat for up to 15-minutes, or even longer in some cases, unless removed by flossing or brushing, or it may skew the test result. You may well be entirely sober but the mouth alcohol could impact your breath test result and show a reading of 0.08% or higher.

Preliminary Alcohol Screen

One other aspect of mouth alcohol residue concerns a breath sample taken on a PAS, or preliminary alcohol screen, which is a mobile device used by police at the scene to see if you have a high degree of alcohol in a breath sample. The test results are admissible as evidence of your BAC if it is shown that the officer complied with Title 17 or the functional elements of

1) A properly functioning machine;

2) Was properly administered, and

3) The operator was qualified2.

The PAS is not considered as reliable as chemical testing but can at least be used as a basis for probable cause to arrest you followed by the request that you submit to breath testing. Drivers under the age of 21 or on probation for a prior DUI conviction are required to blow into the PAS or face arrest.

A PAS reading does not measure deep lung air or your last breaths of air, but the initial air that contains a higher alcohol content and is not an accurate indication of your BAC.

What Are Potential Sources Of Mouth Alcohol?

Mouth alcohol comes from numerous sources including beer, wine or hard alcohol.

But your own health condition or use of other substances that contain at least some alcohol can result in mouth alcohol residue that could influence a breath sample analysis.

Can Dental Work Cause Mouth Alcohol?

If you have braces, dentures, bridges, or crowns, it is very possible that any alcohol you drank became trapped in the dental work.

Can GERD Create Mouth Alcohol?

If there is alcohol in your stomach, then a GERD episode could potentially affect the breath test results and show a false high reading.

 What Is GERD?

Acid reflux includes a chronic condition that many people suffer called GERD, or gastroesophageal reflux disease.

It is more commonly known as severe heartburn.

During digestion, the lower esophageal sphincter opens so as to permit food to pass into the stomach and then closes after eating to prevent food from backing up into the esophagus.

GERD occurs when the lower esophageal sphincter remains open at times, allowing your stomach acid to back up into your esophagus, which is the tube connecting your stomach and mouth, and sometimes into your mouth.

An onset of GERD or severe heartburn can be initiated by eating spicy food, smoking, drinking a small quantity of alcohol or even after eating a large meal.

Can Mouthwash Cause Mouth Alcohol?

Some mouthwashes and breath sprays such as Listerine contain alcohol.

If you used any in the moments before being tested for your BAC, it can potentially cause a positive or high BAC result even though you drank no alcohol.

Are There Medications That Cause Mouth Alcohol?

There are a number of asthma medications that may raise a person’s BAC even though that person has not ingested any alcohol.

Salmaterol is a drug for asthma sufferers and those with COPD, or chronic obstructive pulmonary disease.

These medications contain alcohol that under some circumstances might appear in a breath sample.

The 15 Minute Waiting Period

The breathalyzer machine is supposed to only test alveolar (deep lung) air from the lungs.

But if the machine measures something other than alveolar air (like mouth alcohol), then the test is invalid.

In order to ensure that the breathalyzer machine does not measure mouth alcohol, the police officer who tests someone is required by California law to observe a fifteen minute waiting period before they administer the test where they watch the person and make sure that they do not ingest anything, smoke, drink anything or regurgitate alcohol into their throat or mouth3.

The purpose behind the observation period is to ensure that the subject does not belch, burp, regurgitate or ingest anything that could impact the breathalyzer results for at least 15-minutes prior to testing. This is an acknowledgment that some substances other than an alcoholic beverage can impact the test result. It also is to allow sufficient time for any residual mouth alcohol to dissipate.

Direct Observation

The observation period is supposed to be followed by having an officer directly observed the defendant for the 15-minute period, but this is rarely followed to the letter. In many cases, an officer who has just arrested a defendant will transport the individual to a facility or police station for testing and then prepare the test or present the individual to a technician.

If the trip was at least 15-minutes, the officer will state that at no time did the defendant eat or drink anything. He or she may also comment that no sounds of burping, belching or vomiting was heard or observed, even though the individual was seated behind the officer in the patrol car that may be separated by a mesh or cage.

Even if there is a waiting period at the testing facility or police station, the defendant was likely told to sit somewhere in handcuffs while paperwork was prepared. During this time, a defendant can belch, burp or experience acid reflux just minutes before the test is administered.

Police Report

A review of the police report and test can reveal the period of time between the arrest and the time of testing but will likely not state that the defendant was under continuous direct observation during this time. Further, few if any reports will indicate that the defendant experienced or did not experience acid reflux during this time.

If a defendant had GERD, it is doubtful that an officer will have asked the defendant if he or she suffered from this condition and few defendants are aware that this condition could produce a false high BAC sample.

However, even if the officer failed to observe the defendant for the full 15-minutes, was unaware that the defendant suffered from GERD, or that the individual had burped or belched without the officer’s knowledge, a court will not rule that the breath sample is inadmissible. This omission or negligence by the officer merely goes to the weight of the evidence, though you or your defense attorney can certainly attack the accuracy of the test results4.

Validity of Mouth Alcohol as a Defense

DUI defense attorneys have long used mouth alcohol as a defense to challenge the accuracy of a breath test, whether at the per se or administrative hearing before the DMV regarding the suspension of your driver’s license, or at trial.

But is the mouth alcohol defense a valid one?

There are a number of studies that suggest that it can produce a false high reading in the minutes after mouth alcohol is present but others contend that it has a negligible effect on breath analysis of your BAC and that a 15-minute waiting period is sufficient to allow any residual mouth alcohol to dissipate.


In one study conducted by the National Center for Biotechnology Information (NCBI), 10 subjects were used to determine whether breath alcohol values (BrAV) obtained after the individuals used mouthwash affected the accuracy of breath analysis. Listerine, Lavoris and Scope were used. Samples were obtained after 2, 4, 6, 10 and 15 minute periods after use. Researchers found that the BrAV results fell exponentially after 2-minutes and that after 10-minutes, all maximum values were well below 0.08%. They concluded that a 15-minute period during after the mouthwash was used was sufficient to ensure breath testing accuracy. A subject would have to have used the mouthwash at least 10 minutes before testing to appreciably affect results5.

In another test, 7 subjects rinsed their mouth with a vodka solution and then were tested at 1, 2, 3, 4 and 5 minute intervals after rinsing each time. On average, the BrAV values decreased by 20.4% between 1 and 2 minutes after the rinse. In part 2 of the study, the subjects were given multiple breath tests after rinsing once with the vodka solution. The average time for the subjects BrAV to reach an unbiased level was 9.35 minutes or a range of 4 to 13 minutes. Researchers again concluded that the 15-minute observation period was sufficient and that two breath samples were critical to ensure accurate testing6.

These studies would suggest that use of a mouthwash would only affect breath testing if the defendant rinsed his or her mouth with the substance within a 13-minute period.


In a study of the effects of subjects with GERD, the NCBI tested 15 persons, 10 of whom were diagnosed with GERD. All were dosed with alcohol to reach a BAC of 0.15% and then tested at 20-minute intervals for 8-hours. Post-absorptive BAC and BrAV values were proportional. 3 of the 15 subjects had elevated BAC levels up to 0.105 during the absorptive phase due to passage of gastric alcohol through the lower esophageal sphincter but which was not attributable to eruption or regurgitation. Any breath samples contaminated by GERD were found only when there was a high level of alcohol in the stomach7. This suggests that a subject with GERD who tested with a high BAC level likely consumed enough alcohol so that GERD was inconsequential.

Regarding GERD as a condition that can produce residual mouth alcohol, it is still possible that if a defendant felt the onset of acid reflux just before testing that this could affect his or her BAC results. To support the defense, you would have to have had a diagnosis of GERD at least before your DUI arrest and perhaps a record of prescribed medications to show that it was affecting you. You will also need expert testimony from a physician or researcher on how GERD can affect breath testing of BAC. If your defense attorney can also show innocuous driving conduct (speeding, unlawful U-turn, equipment violation), and inconclusive results of field sobriety testing (if applicable) coupled with a firm diagnosis of GERD, this could be enough to sway a judge or administrative officer at the DMV to not suspend your license, and/or a jury to acquit you of DUI.


In mouth alcohol testing involving dentures, studies seemed to indicate that mouth alcohol trapped in dentures or denture adhesives could have a significant impact on breath analysis8 However, these and other studies concluded that there was little retention of mouth alcohol beyond 20-minutes.

But in another test using subjects with 1) dentures removed; 2) dentures held in place without adhesives; and 3) dentures held with adhesives, the results were somewhat different when samples were tested using the Intoxilyzer 5000 model. Researchers found that 9 of the 24 subjects who had rinsed and kept alcohol in their mouths for 2 minutes before expectorating had positive BrAV results more than 15-minutes after expectoration. The scientists in the study did agree that this was a “worst case” scenario experiment since the subjects had achieved maximum contact with the mouth to “facilitate alcohol retention between dentures and the roof of the mouth and to promote alcohol retention by denture adhesives” ((J Forensic Sci. 37(4); 999-1007 August 1992)). But since over one-third of the subjects had retained mouth alcohol beyond 15-minutes in this test, it is suggestive that dentures can indeed affect breath test results at least under some circumstances.

In cases where a BAC is 0.08% or at least below 0.10%, a defense lawyer can certainly introduce reasonable doubt in cases where a defendant was wearing dentures with or without adhesives by arguing that it is unclear if the breathalyzer was measuring alveolar or deep lung air or a combination of deep lung air and residual mouth alcohol that can be retained beyond a 20-minute period.


If the defendant had used a medication such as Nyquil that contains alcohol, any of these studies can support a mouth alcohol defense provided that you can show insufficient observation of the defendant prior to testing. And, if you were wearing dentures, your attorney can argue that there was a likelihood that the alcohol was retained in your dentures beyond the 20-minute period.

Regarding the drug Salmaterol, which is prescribed for asthma sufferers and those with COPD, or chronic obstructive pulmonary disease, these were tested for residual mouth alcohol. A Spanish study in 2002 found that those taking the drug had a reading of 0.42% BAC within minutes after taking the drug, though other scientists have disputed the results.9. One scientist did opine, however, that the propellant used in asthma sprays can leave a residue of mouth alcohol for several minutes ((Patrick Harding, Breath Alcohol Specificity Study, Indiana University, 2010)). This might be a valid argument for an asthma sufferer who used a spray shortly before breath testing. If the user was a denture wearer, it is possible that the effects of the propellant were trapped in the dentures for longer than 15-minutes.

Essentially, the mouth alcohol defense can be a legitimate and effective one under some circumstances. These may include:

  • A showing that the arresting officer failed to observe the defendant for at least 15-minutes prior to testing
  • That the officer did not directly observe the defendant for at least 15-miinutes even though the defendant was in the officer’s presence
  • That the officer did not ask the defendant if he or she burped, belched or experienced acid reflux just before the test was to be administered
  • That the officer failed to ask the defendant if he or she had used a breath or asthma spray or mouthwash after being stopped and before testing
  • That the officer did not ask the defendant if he or she suffered from GERD
  • That the officer failed to observe or ask the defendant if he or she was wearing dentures
  • That the defendant has a diagnosis of GERD or wears dentures

If the defense introduces expert testimony on mouth alcohol and the prosecution fails to counter with a rebuttal witness, or lacks enough knowledge of the defense to mount an effective cross-examination, then the defendant stands a reasonable chance of introducing reasonable doubt regarding the validity of the breath test results.

Mouth Alcohol FAQ’s

Can Breath Fresheners Cause Mouth Alcohol?

Yes. Breath fresheners and mouthwash can both cause mouth alcohol and can cause a breathalyzer machine to give a high reading because they have alcohol in them.

Can Chewing Tobacco Cause Mouth Alcohol?

Yes. Chewing tobacco sometimes contains raw ethyl alcohol. This is the same type of alcohol found in wine, beer and hard liquor. Chewing tobacco can cause a falsely elevated result from a breathalyzer machine 

Can Dentures Cause Mouth Alcohol?

Yes. Many types of denture adhesives can trap alcohol in someone’s mouth and this can cause a falsely high BAC reading on a breathalyzer machine. Also, dental bridges and dental caps can trap alcohol in crevices and can cause mouth alcohol.

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Next Steps If You Need Help

If you have been arrested and would like to learn more about how attorneys charge.

If you want to understand why its important to have an attorney represent you.

If you would like to discuss a pending case with an attorney contact the Aizman Law Firm at 818-351-9555 for a free confidential consultation.

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  1. People v. Roder (1983) 33 Cal.3d 491, 497-505; Evid. Code §§ 600-607 []
  2. People v. Williams (2002) 28 Cal.4th 408, 417 []
  3. California Code of Regulations, Title 17 []
  4. People v. Adams (1976) 59 Cal.App.3d 559, 567; People v. Williams (2002) 28 Cal.4th 408, 417 []
  5. JAMA 1994 Feb. 16; 271(7):505 []
  6. J Forensic Sci 2012 May; 57(3): 802-5 []
  7. J Forensic Sci 2015 Nov; 60(6): 1516-22 []
  8. Caldwell and Grant, “A Study of Some Factors Affecting the Accuracy of the Breathalyzer,” 8 J Forensic Sci. 149 (1963 []
  9. University of Cadiz, 2002, Juan Manuel Ignacio-Garcia []

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