Approximately 1% of ingested alcohol is eliminated through the skin in the form of gas. The techniques utilized for transdermal alcohol detection capture this gaseous alcohol suspended just over the skin. This identified alcohol is quantified as TAC, which is comparable to the more generally recognized BrAC curves, but its curve is delayed by between 30 minutes and several hours.

TAC curves ascend and reach their maximum at a more languid pace than BrAC curves and stay elevated after BrAC has dropped to zero. This is because the diffusion of alcohol from the blood to the skin is a slower process than through the lungs, causing TAC levels to consistently trail real-time BrAC levels. Consequently, some individuals may manage to drink in between breath test schedules, but continuous monitoring of transdermal alcohol can detect the whole alcohol consumption event.