Permethrin is a medication and chemical widely used as an insecticide, acaricide, and insect repellent. Permethrin is a first-line treatment for scabies. It is used as a cream. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation. It is not known to rapidly harm most mammals or birds, but is toxic to fish and cats.