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Toxicology 101


Toxicology is defined as the science of poisons. More specifically, toxicology is the study of the negative health effects of chemical, physical, or biological agents on living organisms. 

These negative effects can take many forms, from immediate death to subtle changes not detected until months or years later. They may occur at various levels within the body, such as an organ, a type of cell, or a specific biochemical.

Key terms

  • Toxicity is the quality or degree of being toxic or poisonous
  • Toxicants are substances producing negative biological effects. They may be chemical or physical. Their effects may be acute or chronic.
    • Acute toxicity occurs almost immediately after an exposure and may cause death. An acute exposure is usually a single dose or a series of doses received within a 24-hour period.
    • Chronic toxicity is the damage to specific organ systems that takes many months or years to become a recognizable disease.
  • Toxins are peptides or proteins produced by living organisms. Venoms are toxins injected by a bite or sting.
  • Poisons are toxins produced by organisms.
  • Dose is the amount of a substance administered at one time. 
  • Concentration is the amount of a substance found in a certain amount of another substance, such as water, air, soil, food, blood, hair, urine, or breath.


Substances can enter the body from either:

  • Encountering them in the environment (exposure), or
  • Intentionally or unintentionally consuming or administering a certain quantity of a substance.

Substances are present in soil, outdoor air, indoor air, water, and elsewhere. These substances can travel into the body through the skin, eyes, lungs, and digestive tract. 

Dose response

The dose-response relationship relates exposures with changes in body functions or health. In general, the higher the dose, the more severe the response. Within a population, most responses to a toxicant are similar. However, there are differences in how responses may be encountered—some individuals are susceptible and others resistant.

Factors influencing toxicity

A number of factors influence how toxic the substance will be, including:

  • Form and natural chemical activity
  • Dosage, especially dose-time relationship
  • Exposure route
  • Species
  • Life stage, such as infant, young adult, or elderly adult
  • Gender
  • Ability to be absorbed
  • Metabolism
  • Distribution within the body
  • Excretion
  • Health of the individual
  • Nutritional status
  • Presence of other chemicals
  • The time of day a drug or other substance is administered

National Library of Medicine Resources and Databases

  • ToxTutor
    A self-paced tutorial covering key principles of toxicology for navigating chemical and toxicology databases.
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