Animal studies have shown no effects on fertility or teratogenicity, but studies in humans have not been performed. The excretion of permethrin in breastmilk is unknown, and it is recommended that breastfeeding be temporarily discontinued during treatment. Skin reactions are uncommon. Excessive exposure to permethrin can cause nausea, headache, muscle weakness, excessive salivation, shortness of breath, and seizures. Worker exposure to the chemical can be monitored by measurement of the urinary metabolites, while severe overdose may be confirmed by measurement of permethrin in serum or blood plasma.Permethrin does not present any notable genotoxicity or immunotoxicity in humans and farm animals, but is classified by the EPA as a likely human carcinogen when ingested, based on reproducible studies in which mice fed permethrin developed liver and lung tumors. Pharmacokinetics
Permethrin is a chemical categorized in the pyrethroid insecticide group. The chemicals in the pyrethroid family are created to emulate the chemicals found in the chrysanthemum flower. Absorption
Absorption of topical permethrin is minimal. One in vivo study demonstrated 0.5% absorption in the first 48 hours based upon excretion of urinary metabolites. Distribution
Distribution of permethrin has been studied in rat models, with highest amounts accumulating in fat and the brain. This can be explained by the lipophilic nature of the permethrin molecule. Metabolism
Metabolism of permethrin occurs mainly in the liver, where the molecule undergoes oxidation by the cytochrome P450 system, as well as hydrolysis, into metabolites. Elimination of these metabolites occurs via urinary excretion. Stereochemistry
Permethrin has four stereoisomers (two enantiomeric pairs), arising from the two stereocenters in the cyclopropane ring.
Cats
Permethrin is toxic to cats; however, it has little effect on dogs. Pesticide-grade permethrin is toxic to cats. Many cats die after being given flea treatments intended for dogs, or by contact with dogs having recently been treated with permethrin. In cats it may induce hyperexcitability, tremors, seizures, and death.Toxic exposure of permethrin can cause several symptoms, including convulsion, hyperaesthesia, hyperthermia, hypersalivation, and loss of balance and coordination. Exposure to pyrethroid-derived drugs such as permethrin requires treatment by a veterinarian, otherwise the poisoning is often fatal. This intolerance is due to a defect in glucuronosyltransferase, a common detoxification enzyme in other mammals, that also makes the cat intolerant to paracetamol (acetaminophen). The use of any external parasiticides based on permethrin is contraindicated for cats. Aquatic organisms
Permethrin is listed as a "restricted use" substance by the US Environmental Protection Agency (EPA) due to its high toxicity to aquatic organisms, so permethrin and permethrin-contaminated water should be properly disposed of. Permethrin is quite stable, having a half life of 51–71 days in an aqueous environment exposed to light. It is also highly persistent in soil. See also
Benzyl benzoate
DEET
Methoprene
Pyrethrin
Pyrethrum

References
External links
Permethrin in the Pesticide Properties DataBase (PPDB)
Permethrin General Fact Sheet – National Pesticide Information Center
Permethrin Technical Fact Sheet – National Pesticide Information Center
Permethrin-treated Clothing Hot Topic – National Pesticide Information Center
"Health Effects of Permethrin-Impregnated Army Battle-Dress Uniforms", National Research Council (1994, US)
Permethrin Pesticide Information Profile – Extension Toxicology Network
"Permethrin". Drug Information Portal. U.S. National Library of Medicine.