How Alcohol Leaves the Body

The Breakdown of Alcohol
The breakdown, or oxidation, of ethanol occurs in the liver. An enzyme in the liver called alcohol dehydrogenase strips electrons from ethanol to form acetaldehyde. Another enzyme, called aldehyde dehydrogenase, converts the acetaldehyde, in the presence of oxygen, to acetic acid, the main component in vinegar. The molecular structure of acetic acid looks like this:
O
||
H3 C - C - O - H
The || symbol is a double bond between the atoms. When ethanol is oxidized to acetic acid, two protons and two electrons are also produced. The acetic acid can be used to form fatty acids or can be further broken down into carbon dioxide and water.

Once absorbed by the bloodstream, the alcohol leaves the body in three ways:

  • The kidney eliminates 5 percent of alcohol in the urine.
  • The lungs exhale 5 percent of alcohol, which can be detected by breathalyzer devices.
  • The liver chemically breaks down the remaining alcohol into acetic acid.

As a rule of thumb, an average person can eliminate 0.5 oz (15 ml) of alcohol per hour. So, it would take approximately one hour to eliminate the alcohol from a 12 oz (355 ml) can of beer.

The BAC increases when the body absorbs alcohol faster than it can eliminate it. So, because the body can only eliminate about one dose of alcohol per hour, drinking several drinks in an hour will increase your BAC much more than having one drink over a period of an hour or more.