Can Mouthwash Cause You to Fail a Breathalyzer Test?

Yes, mouthwash can cause you to fail a breathalyzer test. Alcohol-based rinses like Listerine contain more alcohol by volume than most wines, and the residue left in your mouth after swishing can push a breath reading to several times the legal limit for about 15 minutes. The effect has nothing to do with your actual blood alcohol, but a device blown into during that window can’t tell the difference.

How High the Reading Can Go, and How Fast It Fades

The numbers are startling. In a Journal of Analytical Toxicology study, subjects who rinsed with Listerine produced an average breath alcohol reading of 0.24 two minutes later, three times the 0.08 limit used in every state.¹ A reading that high suggests a level of intoxication that borders on alcohol poisoning and, in many states, would trigger the enhanced penalties reserved for very high BAC results.

The spike collapses quickly. Ten minutes after rinsing, the same study’s readings had dropped well below 0.08.¹ A separate study of subjects who rinsed with a vodka solution found breath alcohol returned to true baseline in an average of about nine and a half minutes, with the longest case taking thirteen.² Research using beverages from 4% to 95% alcohol found mouth alcohol residuals gone within 10 to 19 minutes.³

The practical danger zone is the first 15 or so minutes. Rinse in a parking lot, pull out, get stopped a few minutes later, and a roadside breath test can show numbers that look like serious impairment when you haven’t had a drink.

Why Mouthwash Shows Up at All

Breathalyzers measure alcohol vapor and are built to sample air coming from deep in your lungs, then convert that to an estimated blood alcohol concentration.⁴ The device cannot distinguish lung vapor from alcohol vapor sitting in your mouth. Common rinses contain roughly 14% to 27% alcohol by volume; Listerine Cool Mint is 21.6%, stronger than most wines.⁵ Swishing coats your entire oral cavity in it, and the breath test treats that residue as if it came from your bloodstream.

Why the Safeguards Against This Don’t Always Catch It

Officers are supposed to observe a subject continuously for 15 to 20 minutes before an evidential breath test. During that window, you can’t eat, drink, smoke, belch, or vomit, since any of those can introduce or reintroduce alcohol to your mouth. Done correctly, the wait is long enough for mouthwash residue to dissipate.²

Modern breathalyzers also run slope-detection software that watches the shape of the alcohol curve as you blow. Deep lung air produces a smooth, gradually rising reading. Mouth alcohol creates jagged spikes or wavy patterns the software is supposed to flag.⁶

Both safeguards fail more often than you would expect. One investigation found that a common slope detector caught mouth alcohol contamination only about 52% of the time. A 2025 study documented three cases where the DataMaster DMT, a widely used evidential breath tester, failed to flag obvious contamination; in one, the device recorded 0.16 without triggering any alert, a result that carries enhanced penalties in many jurisdictions. The researchers noted that manufacturers refuse to sell their devices to independent scientists and treat the detection algorithms as proprietary trade secrets, which makes outside verification effectively impossible.⁶

The observation period has its own real-world problems. Officers running a roadside stop are juggling several tasks at once, and some courts have relaxed the rule to the point where constant, unbroken visual contact throughout the full 15 minutes isn’t strictly required.

What to Do If You’re Asked to Take a Breath Test After Using Mouthwash

Tell the officer right away. You don’t need to volunteer anything else, but a simple statement that you rinsed within the last 15 minutes gives the officer the reason to wait before testing, and it creates a record that could matter later.

Don’t refuse. Every state has an implied consent law: by driving on public roads, you’ve already agreed to chemical testing when an officer has reasonable grounds to suspect impairment. Every state except Wyoming imposes separate penalties for refusal, typically an automatic license suspension, and in at least 12 states refusal is a criminal offense in its own right.⁷ The penalties for refusing can be worse than the penalties for failing.

In many states you can request an independent blood test after complying with the officer’s chosen test. A blood draw measures actual blood alcohol and sidesteps the mouth alcohol problem entirely. If you believe your breath result was inflated by mouthwash, a blood test gives you the strongest evidence to challenge it. The rules on timing and how to request one vary by jurisdiction, so it helps to know your state’s procedure in advance.

Challenging a Contaminated Breath Result

If you’re charged based on a breath reading you think mouthwash inflated, there are several angles a defense attorney will usually look at.

Observation period violations. If the officer didn’t wait the full period, didn’t maintain adequate observation, or you belched or rinsed during the window, the result can be attacked as unreliable.
Slope detector failure. A defense expert can review the breath expirogram, the visual graph of your alcohol curve. Odd patterns suggest mouth alcohol contamination even when the device didn’t flag it.⁶
Lack of duplicate testing. Best practice calls for two samples taken minutes apart. A sharp drop between them is classic mouth alcohol behavior rather than real intoxication.
Borderline readings. Mouth alcohol challenges carry the most weight near the legal limit. A 0.08 or 0.09 is far more plausible as a residue artifact than a 0.15.

None of these guarantees the evidence gets thrown out, but any of them can create reasonable doubt, particularly alongside passing field sobriety tests or no other signs of impairment.

Avoiding the Problem

The simplest fix is an alcohol-free mouthwash. Every major brand sells one, and they work for routine oral hygiene. If you prefer an alcohol-based product, leave at least 15 to 20 minutes between rinsing and driving. Every study on the question shows that buffer is enough for mouth alcohol to clear.³

If you have an ignition interlock device, alcohol-free is the only safe choice. Those devices have no observation period and will lock you out immediately. The same caution applies to anyone whose job involves driving or operating machinery: a morning routine that puts mouthwash right before a commute creates the exact narrow window where a routine stop can turn into a serious legal problem from a product sitting on every bathroom shelf in America.

1
PubMed. Breath Alcohol Values Following Mouthwash Use
2
PubMed. The Rate of Dissipation of Mouth Alcohol in Alcohol Positive Subjects
3
Springer Nature Link. Alcohol Breath Tests – Criterion Times for Avoiding Contamination by Mouth Alcohol
4
National Center for Biotechnology Information. Forensic Sciences Research – Reflections on Variability in the Blood-Breath Ratio of Ethanol and Its Importance When Evidential Breath-Alcohol Instruments Are Used in Law Enforcement
5
Listerine. Alcohol vs Alcohol-Free Mouthwash Which Is Best for You
6
National Center for Biotechnology Information. The Limitations of Mouth Alcohol Detection Systems in Breath Alcohol Testing – Case Reports
7
NHTSA. BAC Test Refusal Penalties