Will mouthwash interfere with the results of a breath alcohol test?

This question is often posed during one of our training classes. Enough so that we spend time demonstrating the effects of what we call residual mouth alcohol, so that alcohol testing technicians are adequately prepared when they encounter a situation where a subject claims their positive test result was due to using mouthwash.

Most mouthwashes contain a small percentage of alcohol designed to kill off mouth germs that cause bad breath.  If a subject consumes mouthwash containing alcohol immediately prior to a breath alcohol test, the remnants of the alcohol from the mouthwash will contaminate the test result. Breath or saliva testing devices will pick up and register the alcohol molecules that remain in the mouth shortly after mouthwash use.  The residual effect of mouth alcohol is known as “residual mouth alcohol” and it lasts no more than 10 to 15 minutes.

So how does an alcohol testing technician respond to a positive alcohol test that may have been influenced by the use of alcohol? There are two ways to handle the mouth alcohol question when doing alcohol testing.

Law Enforcement Protocol

In the case of a preliminary breath test performed by a law enforcement agency, the protocol is to observe every subject for 10 to 15 minutes prior to administering a test to ensure they have not had anything in their mouth. Unlike DOT alcohol testing, most law enforcement protocols conduct only one test when doing preliminary testing, and they expect that test to be positive. Therefore, their protocol requires them to automatically observe a 10 to 15 minute wait period before starting the test.  During that wait time all mouth alcohol molecules will dissipate ruling out residual mouth alcohol as a reason for a positive test result.  (Note that this general protocol applies to law enforcement preliminary breath tests; law enforcement confirmation tests usually follow a different protocol.)

Workplace Testing Protocol

Workplace alcohol testing is often referred to as DOT or non-DOT testing. All DOT alcohol tests follow federal regulations.  In DOT testing the wait period is not observed before the initial test, which is also known as a screening test. The reasoning is that most workplace testing is random, and most tests are negative.  A 15 minute wait period is only observed following a positive screening test where the screening test result is .020 or greater. During this required wait period, the technician must observe the subject to ensure they do not put anything in their mouth. Immediately following the 15 minute wait period, the testing technician must administer a second test, called the confirmation test.

If the initial positive test result was due only to mouth alcohol the results of the second test will be zero.  If the initial positive test was truly due to the subject’s intoxication, the result of the second test will be similar to the initial test.