9 Causes of False Positive Breathalyzer Results in DUI Cases

If you were pulled over and a breath test came back “over the limit,” you might be asking the same question thousands of drivers ask every year: what can cause a false positive breathalyzer test?

Here is the important truth: breathalyzers are not perfect. They are machines operated by humans, and they can be affected by physiology, environment, timing, and device issues. A reading that looks “scientific” on paper can still be wrong, misleading, or legally challengeable.

What Does a Breathalyzer Measure?

Most breathalyzers do not measure “drunk” or “impaired.” They estimate blood alcohol concentration (BAC) based on alcohol detected in your breath.

That distinction matters because breath testing assumes:

• the alcohol detected is coming from deep lung air (not your mouth or throat), and
• the machine is properly calibrated and used correctly.

When those assumptions are wrong, the result can be artificially high, which is exactly what people mean by a “false positive” breathalyzer.

1) Mouth Alcohol (The #1 “False Positive” Problem)

Mouth alcohol is alcohol that is still in your mouth, throat, or upper airway rather than absorbed into your bloodstream. Breathalyzers can “see” it and read it as a higher BAC than you actually have.

Common causes of mouth alcohol include:

• Recent drinking (even if you stopped before driving)
• Burping or belching (brings alcohol vapors up from the stomach)
• Acid reflux / GERD (can move alcohol from the stomach into the throat)
• Vomiting or regurgitation
• Dental work, braces, or dentures (can trap alcohol temporarily)

This is why proper breath test procedure often involves an observation period before the test. If the process is rushed or not followed correctly, mouth alcohol can contaminate the result.

2) Acid Reflux / GERD Can Inflate Breath Test Results

GERD (acid reflux) is one of the most talked-about medical contributors when people research what can cause a false positive breathalyzer test.

Here is the basic idea:

• If stomach contents and vapors come up into your throat, the breath sample may contain alcohol vapors that are not coming from your lungs.
• That can create a reading that looks like a higher BAC than what is in your blood.

Even if you did drink, GERD can potentially make a breath test less reliable, especially if the officer did not properly observe you before testing or you had symptoms like burping, coughing, or nausea.

3) Mouthwash, Breath Spray, and “Alcohol-Containing” Products

Many everyday products contain alcohol and can temporarily trigger higher readings if used close to testing time:

• Mouthwash (some formulas are high in alcohol)
• Breath strips or breath spray
• Certain cough syrups
• Some cold medicines or tinctures

If you used something like this shortly before the test, it may contribute to mouth alcohol, which can lead to a false positive breathalyzer test result (or at least an inaccurately high one).

4) “Ketosis” (Keto Diet, Fasting, Diabetes) and Acetone Issues

Another major topic in false positives: ketones.

When someone is in ketosis (from a strict keto diet, fasting, or uncontrolled diabetes), the body may produce higher levels of acetone. Some breath testing technology can mistakenly react to certain compounds and confuse them with alcohol-related substances.

Important nuance:

• Not every device reacts the same way.
• The risk can depend on the type of breathalyzer and the conditions of testing.

Still, ketosis-related issues are a recognized reason why breath tests are not always as straightforward as they seem.

5) Certain Chemicals and Environmental Exposure

Some environments contain substances that can interfere with breath testing, especially with certain sensor types. Examples people commonly encounter include:

• Paint fumes
• Solvents
• Gasoline vapors
• Industrial chemicals
• Cleaning agents

This can be relevant if you work around chemicals, were pumping gas, were in a garage, or were exposed to fumes shortly before testing. These exposures do not automatically “beat” a DUI case, but they can be part of a larger reliability challenge depending on the facts.

6) Improper Calibration, Maintenance, or Software Issues

Breathalyzers require:

• routine calibration,
• proper maintenance,
• accurate recordkeeping,
• and correct operation.

If the device was not maintained properly or was overdue for calibration, the result can become less reliable. In a DUI defense, maintenance logs and calibration records can become extremely important because they can reveal patterns like:

• missed maintenance intervals,
• errors flagged by the system,
• prior failures or anomalies.

If you are wondering what can cause a false positive breathalyzer test, do not ignore the possibility that the device itself may be part of the issue.

7) Operator Error (Yes, It Happens)

Breath tests are administered by people, and people make mistakes. Examples include:

• Not following the required observation period
• Testing too soon after eating, burping, or vomiting
• Incorrect instructions given to the driver (affects sample quality)
• Improper mouthpiece handling
• Running the test in poor conditions (temperature, contamination, rushed workflow)

Operator error does not always show up in a report as “error.” It often shows up as unreliable or questionable results when the case is reviewed carefully.

8) Breathing Patterns Can Affect Results

How you breathe can change what the machine collects. For example:

• Hyperventilating (fast breathing) can sometimes lower readings.
• Holding your breath can sometimes increase readings.
• Shallow breathing can affect sample quality.

In the real world, people under stress may not breathe normally. If the testing instructions were unclear or the situation was tense, that can matter.

9) Time Matters: Rising BAC and Testing Delays

A breathalyzer result reflects a point in time. If testing happens later than the driving, it may capture a BAC that is higher than it was while you were actually driving, depending on drinking timing and absorption.

This is not always a “false positive,” but it can be a misleading positive if the State uses a later test result to imply a level at the time of driving without accounting for the timeline.

What Should You Do If You Think the Breathalyzer Was Wrong?

If you believe the breath test was inaccurate, focus on actions that protect your case:

1) Write down details immediately

As soon as you can, document:

• what you ate/drank and when,
• whether you used mouthwash or medicine,
• whether you burped, coughed, or felt reflux,
• whether you have GERD/diabetes/keto dieting/fasting,
• what the officer said and did before testing,
• how long it was between the stop and the test.

Small details become big details later.

2) Do not guess or “explain” to police after the fact

Anything you say can be misunderstood or used against you.

3) Talk to a DUI defense lawyer early

Breath testing issues often require quick, strategic moves, including identifying records to request and how to frame the challenges (medical, procedural, mechanical, or timeline-based).

Need Help After a Georgia DUI Arrest? Contact J. Ryan Brown Law

A breathalyzer number is not the whole story, and it is not automatically the final word. If you were charged with DUI and you are researching what can cause a false positive breathalyzer test, there may be legitimate reasons your result is unreliable or overstated.

J. Ryan Brown Law helps people across Georgia fight DUI charges with a defense strategy built around the actual facts, the testing process, and the weaknesses in the State’s evidence.

Request a Free Consultation today.