The allethrins are a pair of related synthetic compounds used in insecticides. They are synthetic pyrethroids, a synthetic form of a chemical found naturally in the chrysanthemum flower. They were first synthesized in the United States by Milton S. Schechter in 1949. Allethrin was the first pyrethroid.
The compounds have low toxicity for humans and birds, and are used in many household insecticides such as RAID as well as mosquito coils. They are however highly toxic to fish and bees. Insects subject to its exposure become paralyzed (nervous system effect) before dying.
They are also used as an ultra-low volume spray for outdoor mosquito control.
Each allethrin consists of the eight possible stereoisomers. A partly stereoselective variant of allethrin I, consisting of only two stereoisomers, is called bioallethrin.