It’s Monday morning, you’re feeling sharp and well-rested as you had an early night and haven't had a drink over the weekend. Yet, during a routine workplace screening, the breathalyser flashes a "Positive" or "Fail" result. After the initial shock wears off, you remember: you used an antiseptic mouthwash just five minutes ago.
This scenario is more common than you might think. It leads to the age-old question that safety managers and drivers ask us every week: Can mouthwash actually trigger a false positive on a breathalyser?
The short answer is yes.
But there is more to the story than just a faulty reading. Understanding the science behind "mouth alcohol" is the key to maintaining a fair and accurate testing environment.
The science of why mouthwash tricks the sensor
The reason mouthwash can interfere with a breathalyser isn't a mystery; it’s simple chemistry. Many popular over-the-counter mouthwashes contain high concentrations of ethanol, often ranging from 20% to 27%. To put that in perspective, that is a higher alcohol content than most wines and many craft beers.
When you use mouthwash, a concentrated "cloud" of alcohol remains in your oral cavity. Professional breathalysers are designed to measure Deep Lung Air, which reflects the alcohol concentration in your bloodstream (BAC).
However, if you blow into a device immediately after using mouthwash, the sensor is overwhelmed by the high-strength ethanol vapor sitting in your mouth.
This results in an incredibly high reading that does not reflect your actual level of intoxication, but rather the "mouth alcohol" left behind from your morning hygiene routine.
The 15-minute rule: The gold standard of testing
In the world of professional drug and alcohol testing, there is one rule that overrides almost everything else: the deprivation period.
To manage the risk of mouthwash, food, or even breath sprays interfering with a result, industry standards require a 15-to-20-minute waiting period before a test is administered. During this time, the subject must not eat, drink, smoke, or use any oral products.
Why 15 minutes? Because mouth alcohol dissipates very quickly. While alcohol in the bloodstream takes hours to metabolise and clear your system, the residual vapor from mouthwash will naturally vanish within minutes. If a subject blows a positive result but claims it was mouthwash, a secondary test taken 15 minutes later will return a 0.00% result if they are telling the truth.
How modern technology handles the mouthwash problem
At Andatech, our professional-grade breathalysers such as the Andatech Prodigy S are equipped with advanced fuel cell sensors. These sensors are far more discriminating than the cheaper semi-conductor versions found in novelty devices.
- Sensitivity: High-end fuel cells are specifically tuned to ethanol and are less likely to be "swamped" by other environmental gases.
- Recovery time: If a device is triggered by mouthwash, a professional unit is designed to clear its internal chamber quickly so it is ready for a verified re-test.
- Procedural prompts: Many of our workplace units can be programmed to prompt the operator to confirm if the 15-minute deprivation period has been observed before the test begins.
Advice for workplace safety managers
For those managing a fleet or a worksite, "mouthwash excuses" can be a point of friction. To keep your safety program running smoothly, we recommend the following:
- Update your policy: Ensure your "Fitness for Duty" policy explicitly mentions the 15-minute waiting period to avoid disputes.
- Neutral language: If a non-negative result occurs, supervisors should remain neutral. Simply state: "As per our protocol, we will wait 15 minutes and conduct a second test to ensure the reading is accurate."
- Don't rely on the "water rinse": While some believe rinsing with water clears mouth alcohol faster, it isn't a substitute for the 15-minute wait. Stick to the clock to ensure legal defensibility.
Read more breathalyser myths from our resource library!
Final thoughts on accuracy and protocol
A breathalyser is a precision instrument, but its accuracy depends on both the quality of the sensor and the protocol of the person using it. Mouthwash can certainly cause a temporary "false" reading, but it should never result in a "false" disciplinary action if the correct procedures are followed.
By using AS3547:2019 certified breathalysers and observing the 20-minute rule, you can ensure that your workplace stays safe, your results stay accurate, and your team stays confident in the system.
Is your team trained on the latest testing protocols? Apart from the right tools, Andatech also provides the expertise. Contact us today for a free consultation on refining your workplace alcohol testing policy.
