For example, the exhalation strength of an asthmatic will indicate how susceptible that person would be to the respiratory effects of exposure to brevetoxin, the toxic compound produced during a red tide.
These indicators also allow researchers to work forward in time to determine an exposure, and prevent it from causing further damage.
This is unlike biomarkers of effect, in which a scientist may work backwards to determine if and what kind of exposure took place, but may be too late to change anything.
These include high specificity (one exposure to one biomarker), linear relationship across time, strong correlation with a health effect, inexpensive study, and consistency (the same exposure will produce the same concentration of the biomarker every time).
From breath to hair to saliva, almost every tissue in the body has been tested as a biomarker of exposure and almost every major environmental pollutant can be identified by biomarkers, including volatile organic chemicals (VOCs) and metals like arsenic or lead.