Alcohol shows up in the breath because it gets absorbed from the mouth, throat, stomach and intestines into the bloodstream. Alcohol­ is not digested upon absorption, nor chemically changed in the bloodstream. As blood circulates through the lungs, some of the alcohol moves across the membranes of the lung’s alveoli, into the air stored within the lungs. Because the alcohol concentration in the breath is related to the concentration in the blood, an approximate measurement can be identified when using a simple ratio formula of breath alcohol to blood alcohol which is 2100:1. This means that 2100 milliliters of alveolar air will contain the same amount of alcohol as 1 milliliter of blood