The smell of alcohol on someone is answered by understanding how the body processes and eliminates ethanol. Ethanol, the type of alcohol found in alcoholic beverages, is a highly volatile compound, meaning it easily evaporates into a gas at normal body temperature. This volatility is the physical property that allows the alcohol to be expelled from the body in an unmetabolized state. The distinct odor people perceive is the direct smell of the raw, unprocessed alcohol leaving the system, not the smell of the body’s digestive process.
The Body’s Processing of Ethanol
Once swallowed, alcohol is rapidly absorbed into the bloodstream, primarily from the small intestine, and then distributed throughout the body’s water-containing tissues. The majority of this alcohol is transported to the liver, the main organ responsible for its breakdown. The metabolism of ethanol begins with the enzyme Alcohol Dehydrogenase (ADH), which is primarily found in the liver cells. ADH converts ethanol into acetaldehyde, a highly toxic chemical compound.
Acetaldehyde is then quickly processed by another enzyme, aldehyde dehydrogenase, into acetate. Acetate is a harmless substance that can be further broken down into carbon dioxide and water. The liver can only metabolize alcohol at a relatively fixed rate, often cited as reducing blood alcohol concentration by about 0.015 per hour. When a person drinks faster than the liver can process, the excess, unmetabolized ethanol remains circulating in the blood.
Elimination Through Breath
The perception of the smell of alcohol is directly linked to the small percentage of unmetabolized ethanol that is eliminated through the lungs. Because alcohol is volatile, it follows the laws of gas exchange once it reaches the vast network of blood vessels in the lungs. The blood carrying the alcohol is pumped into the capillaries surrounding the alveoli, the tiny air sacs in the lungs.
In the alveoli, alcohol molecules transfer from the blood into the air in the lung sacs, similar to the exchange of carbon dioxide. This exchange is possible because the alcohol easily vaporizes from the liquid blood into a gas. The alcohol-saturated air is then expelled with every breath the person takes. The concentration of alcohol in the breath is directly proportional to the concentration of alcohol in the blood, which is why the odor becomes stronger as blood alcohol concentration rises.
Other Routes of Elimination
While the breath is the most noticeable route of elimination, it is not the only one for unmetabolized ethanol. Approximately 5 to 10% of the ingested alcohol is eliminated without being metabolized by the liver. This minor elimination occurs through the kidneys, where alcohol is excreted in the urine, and through the skin, where it is released via perspiration. Although these routes contribute to the overall process of alcohol leaving the body, the amount released is not enough to cause the same level of noticeable odor as the continuous expulsion from the lungs. The smell on the breath is therefore the primary factor in why you can detect alcohol on someone.