A breathalyzer is a device used to estimate the concentration of alcohol in a person’s bloodstream, known as Blood Alcohol Concentration (BAC). Because a direct blood sample is invasive, the breathalyzer provides a non-invasive way to measure the alcohol that has passed from the blood into the lungs. The device calculates an estimated BAC based on the alcohol content found in the breath, which reflects the level of intoxication.
The Path from Drink to Breath
Alcohol begins to enter the bloodstream almost immediately after consumption. A small amount is absorbed directly through the stomach lining, but the majority (approximately 75 to 80 percent) occurs rapidly in the small intestine due to its large surface area. Once absorbed, the alcohol is distributed quickly via the circulatory system throughout the body’s total water content, including organs with high blood flow, such as the brain, liver, and the lungs.
As the blood carrying the alcohol circulates, it passes through the capillaries surrounding the alveoli, the tiny air sacs in the lungs. A gas exchange takes place here, allowing volatile alcohol molecules to evaporate out of the blood and into the air about to be exhaled. This process is governed by Henry’s Law, which states that the concentration of a volatile substance dissolved in a liquid is proportional to its concentration in the air above that liquid.
Breathalyzers utilize this scientific relationship to estimate the amount of alcohol in the blood from the concentration in the breath. The device relies on a standardized conversion factor, known as the blood-to-breath ratio, which is commonly set at 2,100:1. This ratio assumes that 2,100 milliliters of alveolar air contain the same amount of alcohol as 1 milliliter of blood.
Timeline of Initial Detection and Peak Concentration
Alcohol is detectable on the breath almost instantly, beginning the moment it starts crossing the lung membranes and is exhaled. The time it takes to reach Peak Blood Alcohol Concentration (BAC) is the most important measurement for accuracy. For most individuals, the BAC will reach its maximum level between 30 and 90 minutes after the last drink is consumed. During this initial absorption phase, the concentration of alcohol in the blood is rising rapidly.
The breathalyzer is designed to provide the most accurate estimate when the alcohol is in equilibrium, meaning the body has finished absorbing it and the BAC has peaked. If a breath test is administered during the absorption phase, the result may be lower than the true peak concentration the person will eventually reach. Conversely, if tested much later, the body will have entered the elimination phase, where the BAC steadily begins to fall.
Once the peak is reached, the body begins metabolizing and eliminating the alcohol. This elimination occurs through the liver, which breaks down the alcohol using enzymes. This steady elimination phase follows zero-order kinetics, meaning the body removes a constant amount of alcohol per hour, regardless of the overall concentration. The average elimination rate is approximately 0.015 grams per 100 milliliters per hour.
Personal and Environmental Factors Affecting Absorption
The timeline for initial detection and peak concentration is not universal and can be altered by personal and environmental factors. The presence of food in the stomach is one of the most substantial variables affecting the rate of absorption. Eating before or during drinking slows the process because food physically obstructs the alcohol from immediately contacting the stomach lining and entering the blood.
Food, especially meals high in fat and protein, also causes the pyloric valve at the bottom of the stomach to close, which delays the alcohol’s passage into the small intestine. Since the small intestine is the primary site of absorption, keeping the alcohol in the stomach effectively slows its entry into the bloodstream. An empty stomach, by contrast, allows alcohol to pass quickly into the small intestine, resulting in a much faster rise to peak BAC.
Body composition is another factor influencing the final concentration, as alcohol distributes into the body’s total water content. Individuals with a lower body mass or a higher percentage of body fat have less water content in which to dilute the alcohol. For the same amount of alcohol consumed, this leads to a higher overall BAC compared to someone with a higher proportion of lean muscle mass.
The characteristics of the drink itself also play a role in the speed of absorption. Highly concentrated drinks, such as straight spirits, can irritate the stomach lining and delay absorption, while beverages with a moderate concentration, like wine, are absorbed faster. Carbonated drinks, such as those mixed with soda, can increase the rate of gastric emptying, leading to a more rapid peak BAC. Individual metabolic differences in the production of liver enzymes also contribute to variations in the elimination rate.