Pyrethroids are one of the most widely used active ingredients in household insecticides globally, commonly found in household cockroach sprays, mosquito coils and repellents, pet flea collars, and agricultural insecticides.

They are synthetic analogues of natural pyrethrins (extracted from the flower heads of the pyrethrum daisy, Chrysanthemum cinerariifolium).

The mode of action of pyrethroids is to interfere with sodium channels in the insect nervous system — they bind to the alpha subunit of the sodium channel, prolonging the channel's open time.

A normal sodium channel closes within about 1 millisecond after depolarization — the presence of a pyrethroid keeps the channel open for seconds or longer, causing the nerve cell to fire repeatedly; the insect eventually dies in a state of muscle spasm and paralysis.

Toxicity to mammals (including humans) is low — because mammals can rapidly metabolize pyrethroids through liver esterases and the P450 enzyme system, and the structure of mammalian sodium channels has a lower affinity for pyrethroids compared to insect sodium channels.

However, pyrethroids are highly toxic to fish — fish gills absorb pyrethroids directly from the water into the bloodstream, and their detoxification capacity is very low.

Therefore, do not use pyrethroid products near aquariums or outdoor bodies of water.

Common types: permethrin is used for clothing insect-repellent treatment; deltamethrin and cypermethrin are used in indoor insecticide sprays.