You've seen it in the movies; you've seen it on television: A police officer stops a car and asks the driver to take a breathalyzer test. You probably already know that this test is used measure alcohol, but do you know how it works? How can your breath give away the amount of alcohol that has been consumed? It has to do with how the body metabolizes alcohol.

Alcohol absorption

Similar to all food and drinks, when alcohol is consumed it first goes to the stomach and then to the small intestine. A small amount of alcohol is absorbed into the body through the mucous membrane (i.e., the membrane that lines the mouth, throat, and stomach), but the majority of alcohol enters the bloodstream through the walls of the small intestine. Once in the bloodstream, the alcohol is pumped to the brain and other parts of the body, where it is absorbed in proportion to the tissues' water content.

Did you know? Alcohol passes from the stomach to the small intestine via the pyloric valve. If an individual drinks too much too fast, this valve will swell up and close, which makes the person vomit (throw up).

Alcohol is processed and converted to other compounds (i.e., metabolized) in the liver. This is done to remove the alcohol and "detoxify" the blood. The liver does this with a series of enzymes, one of which is alcohol dehydrogenase (ADH), which ultimately convert alcohol into water (H2O) and carbon dioxide (CO2). This is an important function since it prevents alcohol from accumulating to toxic levels that can destroy cells and organs.

Did you know? The liver is responsible for metabolizing alcohol and detoxifying the blood.

However, some alcohol does manage to escape metabolism in the liver; instead, this alcohol is expelled from the body through breath, sweat, and urine. Although this is another way for the body to rid itself of the alcohol, this process accounts for only a small percentage of alcohol that was consumed.

Did you know? A percentage of alcohol that does not get metabolized in the liver is is expelled though one's breath, sweat, and urine.

It takes the body about an hour to metabolize one third to one half ounce (1/3 — 1/2 oz) of alcohol. If you drink more than that in a given hour your liver can no longer keep up. This means that some of the alcohol will NOT get metabolized and will travel throughout your body through the bloodstream. Once that happens, you will find that your brain and nervous system functions will start slowing down; you think and act more slowly...i.e., you will find that you are drunk!

Did you know? The liver can efficiently metabolize 1/3 - 1/2 oz per hour. 

Blood alcohol content (BAC), also referred to as blood alcohol level, is a measure of just is a numerical value of the amount of alcohol that is present in the blood. In addition to the amount of alcohol you consume, factors such as weight, gender, food consumption, emotional state, and rate of drinking also affect how well the body is able to metabolize alcohol, and, therefore, affect an individual's BAC.

For example, people who weigh more will usually have a lower BAC for a given amount of alcohol that is consumed. Gender affects BAC because men generally produce more ADH, the enzyme that breaks down alcohol, than women. Alcohol absorption rates in women are also affected by birth control pills and their menstrual cycle. Food consumed before drinking, especially if it is high in protein, also helps the body metabolize alcohol to water and carbon dioxide more easily, which serves to lower one's BAC.

Did you know? Blood Alcohol Content (BAC) is influenced by amount of alcohol consumed, weight, gender, food consumption, emotional state, and rate of drinking.

Most people begin to show measurable mental impairment at a BAC of around 0.05%. At around 0.10% obvious signs such as an unsteady gait (i.e., stumbling and walking into things/people) appear. Slurred speech accompanies a blood alcohol content of 0.15%, unconsciousness by 0.4%, and above 0.5% the breathing center of the brain and/or heart rhythm can be seriously affected, which can result in death.


To keep reckless drivers in check, police officers will want to know if and how much a driver has been drinking. Originally blood tests were used to measure alcohol concentration in the blood, but the collection process required personnel trained in medical procedures and samples had to be analyzed by lab technicians. Plus, it was a costly and invasive process. In the 1940's breath alcohol testing devices were developed for use by the police. In 1954, Dr. Robert Borkenstein of the Indiana State Police invented the Breathalyzer, used today by law enforcement agencies.

How does the Breathalyzer work? Remember, alcohol that an individual drinks is absorbed into the bloodstream from the mouth, throat, stomach, and small intestines. As described above, alcohol that is not metabolized by the liver will stay in the blood and will eventually travel to the lungs. When alcohol is present in the blood, some of the alcohol moves across the membrane of the blood vessels and the lung's air sacs (alveoli) into the air.

Did you know? In the alveoli of the lungs, un-metabolized alcohol in the blood is transferred to the air that will be exhaled.

The concentration of the alcohol in exhaled air is directly related to the concentration of the alcohol in the blood. As the air is exhaled, the alcohol is detected by the Breathalyzer device. Because the concentration of alcohol in the breath is related to that in the blood, BAC can be calculated by measuring alcohol on the breath. The ratio of breath alcohol to blood alcohol is 2100:1. This means that 2100 ml of alveolar air will contain the same amount of alcohol as 1 ml of blood. It's a matter of a simple calculation to convert breath alcohol levels to blood alcohol concentration.

Did you know? The amount of alcohol in one's breath is directly proportional to the amount of alcohol in the blood.

The breathalyzer itself is a really cool device. It measures alcohol levels through a chemical reaction in which a reddish-orange dichromate ion changes to green when it reacts with alcohol; the degree of colour change indicates the level of alcohol expelled in the air. More green means more alcohol.

The legal limit for driving in Canada is 0.08% (assuming, of course, you are over 19 years old...if you're under 19, than you will have a few more problems to deal with!), which equates to 80 mg of alcohol in 100 ml of blood. A Breathalyzer immediately tells a police officer if a driver is over that limit. Regardless of what people tell you, a breath mint just isn't enough to fool a avoid the whole experience all together by NOT drinking and diving.


Graves, Bonnie. Alcohol use and abuse, Perspectives on Physical Health, 2000 Capstone Press, Minnesota

Teen Alcoholism, 2001 Greenhaven Press Inc, San Diego CA

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Fiona Wyse is a Trent University graduate with a Degree in German Studies and Philosophy. Passionate about writing, research, and continuing her education, Fiona enjoys sharing information that she has learned with those who share an interest.


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