Transdermal Alcohol Content (TAC) vs. Blood Alcohol Content (BAC) Explained

What is Transdermal Alcohol Content?

TAC, or transdermal alcohol content, is the small amount of alcohol that your body releases through your skin when you drink. This alcohol is released even if you are not sweating, as your skin is porous and breathable. Just like how your Blood Alcohol Content (BAC) goes up when you drink, your TAC will also start to rise as you consume alcohol. Because the alcohol you drink has to move through your body to get to your skin surface layer, there is a delay between when you start drinking, and when you will see your TAC values rise. Your TAC values will increase the more you drink, and will follow a bell curve pattern similar to your BAC values. BACtrack Skyn will measure your TAC value every 20 seconds, but it’s best to review your TAC data as a curving pattern over the course of your drinking session.

What does the TAC graph mean?

In your BACtrack Skyn app, you will see a graph of your TAC data. The horizontal line at the bottom represents the time of TAC data collection, and the vertical axis shows your TAC value at each 20 second interval. The most recent TAC values measured will be in the region of the graph farthest to the right. At any given time, the graph shows your instantaneous TAC value, which you can think of as an estimation of the current amount of alcohol your body is releasing. This represents the alcohol signal from what you have consumed in the past 30-45 minutes.

Your TAC data will start to rise as you drink, but with a time delay as the alcohol molecules have to get through your body to your skin. Over the course of your drinking session, your TAC values will rise in the shape of a bell curve, and may continue to rise even after you have stopped drinking. This is because there is still some alcohol in your body that has not yet gotten to your skin surface even if you have consumed your last drink. As time goes on, the TAC values will begin to decrease in a gentle slope, and after your body has excreted all alcohol from your drinking session, you will see a bell curve like below.