What is Blood Alcohol Content?

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  • Written By: Jacob Queen
  • Edited By: Lauren Fritsky
  • Last Modified Date: 13 February 2020
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Blood alcohol content is a measurement of the quantity of alcohol in a person’s blood stream. It is often measured for legal purposes using several different methods, including breathalyzers and blood tests. According to most experts, once blood alcohol content reaches 4 one-hundredths of a percent, that is usually enough to begin impairing someone’s abilities. Over time, blood alcohol content will generally decrease as the body metabolizes the alcohol, which is actually treated like a toxin within the digestive system. The physical size of a person also plays a role in determining how much alcohol it takes to raise blood alcohol level.

Alcohol is able to absorb through the tissues in the mouth, so a person’s blood alcohol level generally begins to rise as soon as he takes his first drink. Alcohol is also absorbed in the digestive system, especially in a person's small intestine. Once it enters the blood stream, the body starts to treat it as a toxin.

When the body identifies a toxic substance, it uses the liver to facilitate digestion. The liver has the job of eliminating toxins by converting them into substances that the body can tolerate. This is why alcohol can have a negative effect on the liver. Eventually, a person's liver can be exhausted through the process of detoxifying the blood stream. All this work can cause the liver to develop scar tissue, which is the major characteristic of cirrhosis.


When people consume alcohol for a long time, they eventually develop a stronger tolerance, and it may require a higher blood alcohol content to cause major intoxication. By contrast, in the very beginning, it may require very little alcohol to produce a pronounced effect and decrease a person’s ability to function properly. Many legal definitions of intoxication are based around a middle ground, and they may vary significantly in different places. For instance, 0.10% is a common legal limit in many areas, but it can also be set much lower than that.

Breathalyzers measure blood alcohol level by analyzing the air coming from the lungs, which release a certain amount of alcohol vapor when a person is intoxicated. The breath test is generally considered reliable enough for quick use in the field for police work. Some people also take blood tests as well for results that may potentially be more accurate.



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