Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and insect repellent. 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 dangerously toxic to cats and fish. In general, it has a low mammalian toxicity and is poorly absorbed by skin. Permethrin is used on humans to eradicate parasites such as head lice or mites responsible for scabies and as a pest-repellent clothing treatment. Permethrin is more effective in reducing itch persistence than crotamiton or lindane. The common prescription is a 5% concentration of permethrin for scabies and a 1% concentration for the over-the-counter (OTC) treatment for head lice or crabs.
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