A home experiment - will mouthwash make me fail a breathalyzer test?

thewaltman By thewaltman, 21st Dec 2009 | Follow this author | RSS Feed | Short URL http://nut.bz/2687-39_/
Posted in Wikinut>Guides>Science>Home Experiments

There seems to be some uncertainty about whether using mouthwash could cause a false positive breathalyser result... so I did a little experiment.

My home breathalyser device

First things first. I did not use any officially sanctioned piece of kit, and it certainly wasn't anything the police would use. It is basically a cheap personal breathalyzer that I was given as my Secret Santa gift at work, and this is just a home experiment.

However, both myself and my wife have tried it a few times and it seemed to meet the general UK guidelines - i.e. after one drink it registered a pass, any more that that and it failed.

So for the purpose of this experiment, it seemed a valid piece of kit to use. It's also very simple - if you are OK to drive you get a safe message, otherwise it flashes danger.

The mouthwash

For the mouthwash I used a bottle of Coolmint Listerine Anti-Bacterial Mouthwash. This lists alcohol as the second ingredient after water, and smells pretty potent.

The experiments all followed the instructions, which are: "Pour 20ml into a glass, rinse around teeth and gums for 30 seconds then spit out."

The mouth was not washed out after the rinse, as per the instructions.

Test 1 - sober man

OK, so my first effort started with me in a sober state (no laughing at the back). To prove this I took a breathalyser test. The result - safe.

For the record I'm a 5 foot 11, fairly well built bloke. I took a shot of the mouthwash, rolled it around my mouth for 30 seconds and spit out.

Then I immediately ran a test on the breathalyzer. Danger!

The mouthwash generated an immediate result... interesting. However, I then waited exactly 2 minutes and took another breathalyser test.

This time - safe. So the conclusion is that the mouthwash did have an impact on the result of the test, but only for a very short period. So guys, I'd say your chance of being stopped by the police and breathalysed within 2 minutes of using the mouthwash is pretty minimal. And I'd also recommend you don't use mouthwash as an excuse...

Test 2 - sober woman

Then I repeated exactly the same steps with my good lady wife. And for the record she is a 5 foot 6, slim built lady.

After the mouthwash, exactly the same results. Initially a danger on the first test, than after 2 minutes a safe.

So the same applies to the ladies - mouthwash is no excuse for getting caught over the limit the morning after.

Test 3 - man after 1 beer

OK I thought, what if the mouthwash was used after one beer? A single drink should result in a pass, so would the addition of the mouthwash tip the balance?

Again, in the interests of science I will document the beer in question. It was a 500ml bottle of Batemans XXXB Classic Premium Pale Ale. The alcohol content was 4.8% so a good study beer for this test.

I quaffed the booze steadily, and once finished retook a breathalyzer test. The result - safe. So as expected, a single beer meets the guidelines.

Then I swilled the teeth and gums with mouthwash, and took another test - as when I was sober, the first test returned Danger.

And after 2 minutes, back to safe. So it seems that even combined with other alcohol

The conclusion

Mouthwash is no excuse for drink driving, nor will it trigger a false positive result unless you happen to be swilling with Listerine while driving - which in itself is probably an offence.

So stay safe, don't drink and drive, and don't worry about using mouthwash in the morning.


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Interested in many topics, master of none. Learning more everyday though...

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author avatar Josh
25th Dec 2009 (#)

As a Driver Ed teacher, I get this question all the time from my (15-year-old!) students. Thanks for performing the experiment.

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author avatar Breathtester
26th Dec 2009 (#)

Most mouthwash contains alcohol and after using it, residual alcohol is left in the mouth. This is what the breathalyzer is sensing. Law Enforcement normally tries to engage a dui suspect for 10-15 minutes prior to a roadside breath test to ensure that the instrument is reading breath alcohol, not residual alcohol. For more info go to www.lifeguardbreathtester.com qand there's good info on this effect.

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author avatar Bill spark
4th Nov 2010 (#)

what happens if you have a close fitting pallet like mine that traps fluids and it stays in your mouth longer as I have failed a breath test at work after taking a mouthwash 10 mins earlier

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