There are a lot of urban myths about breathalyzers being tricked by mouthwash. This particular urban myth is actually true…sort of.

Can Mouthwash Make You Fail a Breathalyzer Test?

Some mouthwashes will produce false readings on a breathalyzer machine. And these readings are not just a little false, they are way off.

For example. If a sober person gargles and spits with the original formula Listerine immediately before taking a breath test your test their breath test results would be as high as .75.  A .75 Blood Alcohol Reading is over nine times the legal limit of .08. Few humans can survive having a blood alcohol content over .50 let alone a .75.

“Attorney Demos How Mouthwash Can Make You Fail a Breathalyzer Test”

So mouth wash can have a huge effect on breathalyzer machines but here is why. First, Listerine is an alcohol-based mouthwash. Listerine is about 47% alcohol. That is about the same amount of alcohol as 80-proof whiskey.

But a person would have to drink about a dozen shots of whiskey to get to a .75 (if they didn’t die or pass out first) but the same person can produce a .75 reading after rinsing their mouth with a cap full of Listerine. These strange results are caused by “mouth alcohol”.

What is Mouth Alcohol?

Breathalyzers are designed to measure the tiny particles of alcohol that escape from your blood into your lung and out through your breath. The amount of alcohol in a drunk person’s breath is very small so breathalyzer machines are very sensitive.

However, when a person puts alcohol in the mouth or throat, some of that alcohol gets trapped in their saliva, in between their teeth, under the tongue, and in any food or gun that might be in their mouth at the time.

After putting alcohol in your mouth, alcohol fumes will escape from your saliva and mouth at much higher concentrations than the alcohol that is in a drunk person’s breath. This concentrated alcohol escaping from your mouth saliva is called “mouth alcohol”.

Mouth alcohol is much more potent than blood alcohol but most breathalyzer machines can’t tell the difference between mouth alcohol and blood alcohol.

How Long Does Mouth Alcohol Last?

Additionally, mouth alcohol is different than blood alcohol because mouth alcohol disappears really quickly compared to blood alcohol. Mouth alcohol usually is 100% gone within 20-30 minutes after a person puts alcohol in their mouth.

Can Breathalyzers Detect Mouth Alcohol?

Most breathalyzer machines cannot detect mouth alcohol at all. The portable breathalyzer machines that officers use on the side of the road cannot tell the difference between mouth alcohol and blood alcohol. The ignition interlock devices that are installed in cars after a DUI conviction, also cannot tell the difference between mouth alcohol and blood alcohol.

However, one indicator of mouth alcohol includes rapid decreases in blood alcohol readings. For example, a person who uses Listerine mouth wash may produce a .75 reading seconds after spitting, but 30 minutes later they will be a 0.00. A person who was actually just a .08 would take 8 to 12 hours to reach a 0.00. So a police officer can detect mouth alcohol by simply retesting the same person a few minutes later.

That is why ignition interlocks are often programmed to retest 5 minutes after a failed breath test. If the original test was caused by mouth alcohol, the retest should detect either no alcohol or very little alcohol. This would not be the case with someone who had been actually drinking. If you ever fail an ignition interlock test and you were not drinking alcohol, make sure to retest as soon as possible.

The only devices that have any ability to tell if reading is from mouth alcohol are the breathalyzer machines at the police station, but these devices do not always detect mouth alcohol.

In Virginia, all police departments use a breathalyzer device called an EC/IR II for testing people’s breath at the police station. The EC/IR II stands for Electro-Chemical/InfraRed II. The electrochemical part refers to the electrochemical cell that is used to produce the actual blood alcohol content number. The infrared portion of the name refers to the infrared sensor in the machine that detects alcohol using an infrared laser. The laser’s job is to constantly measure the alcohol content of the breath sample as it comes into the machine to detect unusual changes in the blood alcohol content.

If there are sudden changes in the infrared reading this can be a sign of mouth alcohol caused by someone burping or regurgitation alcohol while they are in the middle of blowing into the machine.

While the machine may be able to detect this type of mouth alcohol, is uncertain whether the machine is capable of detecting other more subtle forms of mouth alcohol. Additionally, not all EC/IR IIs are programmed to use this function and it is unclear whether the EC/IR IIs used by the police in Virginia are set up to actually detect this type of mouth alcohol.

If you burp, belch, or put anything containing alcohol in your mouth within 20 to 30 minutes of failing a breath test, make sure to talk to an attorney about your case.

The EC/IR II at the police station is also programmed to take two breath samples within a minute or two of each other. The machine takes two tests and compares the results. If the results match close enough then the machine will produce a blood alcohol result. If the two tests do not match the machine will demand a third test. If at least two of the three breath results don’t match then the machine will not produce a result.

By retesting at least twice, the breath machine may be able to detect extreme mouth alcohol. However, if a person has some blood alcohol and some mouth alcohol the machine may not be able to detect that. So for example. If you are slightly under the legal limit but there is some mouth alcohol present while testing, the small amount of mouth alcohol can push you over the legal limit but be too small for the machine to detect.

Mouthwash and Ignition Interlock

Because alcohol-based mouthwash can cause failed breathalyzer readings, Virginia ASAP will not allow people in the ASAP program to use alcohol-based mouthwash. Using Listerine or other alcohol-based mouthwashes can result in a probation violation. If you have an ignition interlock in your car, it is definitely a good idea to obey this rule.

Also, many foods and drinks and even some cough drops or gums may contain alcohol (For example Honey Buns, vanilla extract, white bread, and cliff bars). So it is a good idea to not eat or drink or chew chum within 30 minutes of taking an ignition interlock test. And because ignition interlock does random retests while driving, don’t eat or drink or chew gum while driving.