Allethrin is a pyrethroid insecticide and modulator of voltage-gated sodium channels (NaV). It delays channel deactivation in cockroach giant axons when used at a concentration of 1 μM. Allethrin is 100-fold more potent at insect than rat NaV1.8 channels expressed in Xenopus oocytes. It decreases egg production by and is lethal to mosquitoes (LC50 = 0.01%). Allethrin induces production of reactive oxygen species (ROS), lipid peroxidation, and apoptosis in rat primary Leydig cells. In vivo, the smoke of an allethrin-based mosquito coil increases levels of the hepatic enzymes ALT and AST and induces hepatocyte apoptosis as well as emphysema and lung hyperplasia in mice.