Assessing Human Health Risk from Pesticides

On this page:

Human Health Risk Assessment for Pesticides

We use risk assessments to make informed decisions about approving new pesticides and new uses of registered pesticides, and during our regular review of existing pesticides.

Our human health risk assessments estimate the nature and probability of harmful health effects in people who may be exposed to pesticides:

  • in the food and water they consume;
  • in the air they breathe;
  • through their work; or
  • as a result of activities that may lead to contact with pesticide residues on treated surfaces.

We review all scientific data on the pesticide and develop comprehensive risk assessments.

When our assessments show that risks from a pesticide need to be reduced, we modify where and how it can be used. If a pesticide does not meet our safety standard, after considering all appropriate risk reduction measures, we will not allow it to be used. 

Process for Human Health Assessment for Pesticides 

We develop our human health risk assessments using the National Research Council’s four-step process:

  • Step One: Hazard Identification (Toxicity)
  • Step Two: Dose-Response Assessment
  • Step Three: Exposure Assessment
  • Step Four: Risk Characterization

Step One: Hazard Identification (Toxicology)

  • We examine whether a pesticide has the potential to cause harm to humans, and if so, under what circumstances.
  • Our scientists evaluate many toxicity studies that typically are conducted on animals by pesticide companies in independent laboratories.

Learn more about toxicity tests for human health assessments. 

Step Two: Dose-Response Assessment

Paracelsus, the Swiss physician and alchemist, the “father” of modern toxicology (1493-1541) said, "The dose makes the poison."

In other words, the amount of a substance a person is exposed to is as important as how toxic the pesticide might be. For example, small doses of aspirin can be beneficial to people, but at very high doses, this common medicine can be deadly. In some individuals, even at very low doses, aspirin may be deadly.

  • Dose-response assessment examines the numerical relationship between exposure and effects.
  • We consider the dose levels at which harmful effects are observed in test animals.
  • We use these dose levels to calculate what an equal dose in would be in humans.​

Step Three: Exposure Assessment

Our exposure assessment examines what is known about the frequency, timing and levels of contact with a pesticide.

Typical sources of pesticide exposure:

You might use pesticides in and around your home to control insects, weeds, mold, mildew, bacteria, lawn and garden pests and to protect your pets from pests such as fleas. Pesticides may also be used as insect repellants that are directly applied to the skin or clothing.

  • Occupational exposure (workers and applicators)
    Pesticide applicators, vegetable and fruit pickers and others who work around pesticides can be exposed during their jobs (occupational exposure).
  • Cumulative risk for pesticide groups that share a common mechanism of toxicity

Step Four: Risk Characterization

Risk characterization is the final step in assessing human health risks from pesticides.

  • Hazard, dose-response and exposure assessments are combined to describe the overall risk from a pesticide.
  • We explain the assumptions and safety factors used in assessing exposure as well as the uncertainties that are built into the dose-response assessment.
  • The strength of the overall database is considered
  • We draw conclusions about the nature and extent of the risk from exposure to the pesticide.

Top of Page

Safety Factors

We recognize that effects vary between animals of different species and from person to person. To account for this variability, uncertainty factors are built into the risk assessment. These uncertainty factors create an additional margin of safety for protecting people who may be exposed to the pesticides. The pesticide law requires us to use an extra 10-fold safety factor, if necessary, to protect infants and children from effects of the pesticide.

Risk Equation

The risk to human health from pesticide exposure depends on both the toxicity of the pesticide and the likelihood of people coming into contact with it. Simply put,


At least some exposure and some toxicity are required to result in a risk. For example,

  • if a pesticide is very poisonous, but no people are exposed, there is no risk, or
  • alternately, ample exposure to a non-toxic pesticide poses no risk.

However, usually when pesticides are used, there is some toxicity and exposure, which means there is a potential for risk.

For More Information

Top of Page