Toxicology Explained

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 are helpful at low doses can be used as medicines, but at higher doses can be harmful.  Toxicologists use information from dose-response studies for a chemical to calculate the dose likely to be safe for people.

"All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy."
- Paracelsus

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 Assessment

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 then compared to the dose determined to be safe based upon dose-response studies.  If  there is a concern about negative health effects, the risk assessor will make suggestions to help people avoid or reduce exposure. The results of risk assessments carried out by the Public Health Toxicology team can be found on our Environmental Exposure Assessments page.