Health Effects

Permethrin is a member of the pyrethroid class of pesticides. Similar to other pyrethroids, permethrin alters nerve function by modifying the normal biochemistry and physiology of nerve membrane sodium channels. However, EPA is not currently following a cumulative risk approach based on a common mechanism of toxicity for the pyrethroids. Although all pyrethroids interact with sodium channels, there are multiple types of sodium channels and it is currently unknown whether the pyrethroids have similar effects on all channels. Nor do we have a clear understanding of effects on key downstream neuronal function e.g., nerve excitability, nor do we understand how these key events interact to produce their compound specific patterns of neurotoxicity. There is ongoing research by the EPA’s Office of Research and Development and pyrethroid registrants to evaluate the differential biochemical and physiological actions of pyrethroids in mammals. This research is expected to be completed by 2007. When available, the Agency will consider this research and make a determination of common mechanism as a basis for assessing cumulative risk. Therefore, the human health risk assessment and RED document only considered the effects of permethrin.

Additionally, the Agency classified permethrin as “Likely to be Carcinogenic to Humans” by the oral route. This classification was based on two reproducible benign tumor types (lung and liver) in the mouse, equivocal evidence of carcinogenicity in Long- Evans rats, and supporting structural activity relationship information.
http://www.epa.gov/oppsrrd1/REDs/factsheets/permethrin_fs.htm