Hypersusceptibility - Excessive reaction following exposure to a given amount or concentration of a substance as compared with the large majority of other exposed subjects.

Hypersensitive – 1 : Excessively or abnormally sensitive; 2 : Abnormally susceptible physiologically to a specific agent (as a drug or antigen).


Because some people have a different variant of the enzyme PON1, which is one of the enzymes that the body uses to break down chlorpyrifos, they may be more sensitive to gross misuse of the product (for example, exposure via deliberate ingestion). The human body, however, has many mechanisms for breaking down chlorpyrifos, and PON1 is not the primary one. Differences in human susceptibility to chlorpyrifos have never been demonstrated as a result of PON1 variations except in the laboratory at doses more than 1,000 times greater than expected real-world exposures from authorized product use.

Further Resources

“Chlorpyrifos Studies: The Debate is in the Details,” Dow AgroSciences (PDF)

“Dow AgroSciences’ Response to EPA’s Preliminary Chlorpyrifos Human Health Assessment,” Dow AgroSciences. Submitted October 5, 2011.

U.S. Department of Health & Human Services. Environmental Health & Toxicology site. IUPAC glossary:

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