The need to assess the real health effects from exposure to chemicals is hampered by our inadequate understanding of what chemicals people are exposed to and to what degree these exposures might cause short term (acute) or long term (chronic) adverse health effects.

Human Biomonitoring is the measurement of toxic substances in the human body. The purpose of Human Biomonitoring is to determine if you have been exposed to a toxic substance, how much of that toxic substance is in your body, and whether the amount of that toxic substance in your body is enough to cause an adverse health effect. Toxic substances generally enter the body through one of three routes: ingestion, inhalation, or dermal penetration.

The amount of substance available for toxic action depends on a number of factors. In most cases, the substance is absorbed to some degree into the bloodstream where it is distributed throughout the body.

At this point, toxic substances have three possible fates: they are stored, excreted, or metabolized. Most chemicals undergo some combination of all three. Storage typically occurs in a reservoir such as bone or adipose tissue. Excretion involves the elimination of substances or their metabolites through urine, feces, saliva, sweat, or exhalation. Substances that are metabolized are often chemically altered to make excretion of the substance easier.

The time (antecedent or present), duration, and intensity of exposure to a particular substance will dictate the choice of human tissue that is sampled to monitor the substance or its metabolites. Most Human Biomonitoring involves sampling humans for whole blood or serum and urine. However, meaningful results have been achieved from sampling saliva, feces, hair, nails, teeth, breath, and sweat.