Permethrin is an insecticidal substance originating from the flowers of Chrysanthemum cinerarifolium, being a synthetic pyrethroid that acts directly on insects, in particular on their central nervous system, inducing electrochemical changes that lead to their death by spasms, paralysis and death of the vector. It also has an irritating effect, causing an excito-repellent response, resulting in hyperactivity and rapid knock-down, feeding inhibition, shorter insect landing times, and directionless flights (flight disorientation), which, together, allow to reduce the ability of the vector to chop.
To exert its action, the insect just needs to come into contact with the sprayed tissues, that is, it just needs to be exposed by ingestion, breathing or contact with the skin.
Permethrin is practically not absorbed by human skin. However, it can cause an allergic skin reaction and, if it gets in the eyes, it can cause eye irritation.