This occurs at the sodium ion channels in the nerve cell membrane. Nerve cell membranes have a specific electrical charge. Neurotransmitters help nerve cells communicate. Electrical messages sent between nerve cells allow them to generate a response, like a movement in an animal or insect. Even though pyrethrins and pyrethroids are nerve poisons, they are not cholinesterase inhibitors like organophosphate or carbamate insecticides.
Synergists work by restricting an enzyme that insects use to detoxify the pyrethrins.
There are many different types of pyrethroids, but the remainder of this fact sheet will deal with pyrethrins. Information on specific pyrethroids is available in other fact sheets. See box on laboratory testing. In these tests, laboratory animals are purposely fed a pesticide at high doses to cause toxic effects. These tests help scientists judge how these chemicals might affect humans, domestic animals, and wildlife in cases of overexposure.