An alveolar breath measurement can show that a volatile chemical is present in exhaled air. That does not necessarily reveal how the chemical entered the body. A historical review illustrates the distinction with tetrachloroethylene, a solvent used in dry cleaning and degreasing.
Hake and Stewart reviewed an experiment in which volunteers immersed one thumb in a liquid solvent and investigators collected serial breath samples. Tetrachloroethylene was measurable in breath after skin contact. Its breath concentrations declined more slowly than those of the other solvents examined in that experiment.
A single breath result does not apportion dermal and inhaled exposure. A reconstruction would consider the sampling time, workplace air measurements, whether liquid contacted the skin, and the duration of each possible exposure. The historical experiment is evidence that skin uptake can contribute to a breath measurement.
Hake and Stewart, Environmental Health Perspectives ยท Full text