Using mouthwash can temporarily cause a positive reading on a preliminary alcohol breath test, even without consuming alcoholic beverages. Many common oral hygiene products contain a high concentration of ethyl alcohol, the same substance found in spirits. Immediately after rinsing, residual alcohol vapor in the mouth is detectable by testing devices, leading to a false indication of intoxication. This occurs because breath testing technology is sensitive to alcohol vapor, regardless of its source.
Alcohol Content in Oral Hygiene Products
Many commercial mouthwashes use ethanol, a type of alcohol, as a solvent or as an antimicrobial agent to kill bacteria. These products can contain surprisingly high concentrations of alcohol by volume. The alcohol content in these oral rinses typically ranges from 14% to 27% or higher, with some popular brands exceeding 20% alcohol content. Some mouthwashes contain a higher concentration of alcohol than many alcoholic beverages. While mouthwash is not meant to be swallowed, other products like breath sprays, certain cough syrups, and dental rinses also contain alcohol and can present the same temporary problem.
Why Breathalyzers Detect Mouth Alcohol
Breath testing devices, especially the portable preliminary breath tests (PBTs) used at the roadside, measure the concentration of alcohol vapor in the air exhaled from the lungs. The device estimates a person’s Blood Alcohol Concentration (BAC) based on the alcohol expelled from the deep lung air, also known as alveolar air. This deep lung alcohol reflects a person’s level of intoxication, as it has been absorbed into the bloodstream.
When mouthwash is used, a significant amount of alcohol residue, called “mouth alcohol,” remains temporarily in the oral cavity and throat. This vaporized alcohol concentration is extremely high immediately after use. When a person exhales into the breathalyzer, the device detects this concentrated mouth alcohol before the deep lung air, causing an immediate spike in the reading.
This high result is a false positive because it reflects the alcohol residue in the mouth, not the systemic alcohol level in the bloodstream. Even advanced evidentiary breath testing machines are sensitive enough to pick up this residual alcohol, which can lead to an inaccurate reading that does not reflect true intoxication.
How Long the Effect Lasts and Prevention Steps
The high readings caused by mouth alcohol are temporary and dissipate quickly. The residual alcohol in the mouth evaporates or is swallowed within a short time frame, usually between 10 and 20 minutes after using the product. This rapid clearance is why standard law enforcement protocol requires a mandatory observation period before administering a breath test.
For an accurate test, the officer typically must observe the person for at least 15 to 20 minutes before the test is conducted. This observation period is intended to ensure that the subject does not ingest or regurgitate anything that could contaminate the sample. If a preliminary test shows an elevated level, the standard procedure is to wait and conduct a retest to ensure the reading reflects deep lung alcohol.
If you have recently used an alcohol-based mouthwash and are asked to submit to a breath test, the most practical step is to thoroughly rinse your mouth with water. Waiting the standard 15-minute period is sufficient for the residual alcohol to dissipate and for the reading to return to an accurate level. The later, more accurate evidential tests, such as a subsequent breath test or a blood test, are designed to confirm impairment by measuring deep lung alcohol or blood alcohol concentration, making them less susceptible to mouthwash residue.