Toxicology is the science of determining health risks from exposure to chemicals. Almost any chemical can be harmful depending on the dose (the amount of chemical and amount of time a person is exposed, in addition to how often a person is exposed) and route of exposure (whether the chemical is eaten, breathed in, or touches your skin). Acute (short-term) exposure and chronic (long-term) exposures can have different effects on a person’s health.
The Dose Makes the Poison
The basic principle of toxicology is that "the dose makes the poison," which is a concept attributed to the 15th-century physician Paracelsus. It is understood that a chemical's effects are dose-dependent, which means that the effect is determined by how much a person is exposed to. For example, chemicals that have helpful or therapeutic uses are harmful at a higher dose. Toxicologists use information from dose-response studies to calculate safe levels of contaminants that are expected to harm a person's health. For more information about the dose-response relationship, click here.
"All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy."
Routes of Exposure
How a chemical enters into a person's body can make a difference with how much of it is absorbed, and can determine whether or not the exposure will cause harm. Oral exposure is when something is ingested, usually through food or drink. Inhalation exposure is when a person breathes something that is in the air. Dermal exposure happens when something is absorbed through a person's skin. A chemical that is harmful by one route of exposure may not be very harmful at all by another.
Risk assessors calculate the total exposure dose by adding the amount of chemicals entering your body by all of the potential exposure routes. This information is the compared to data from dose-response studies to determine whether the total exposure is will harm a person's health. If there is a concern about negative health effects, then the risk assessor may make suggestions to help people avoid or reduce exposure.