Pyrethrum is a natural insecticide extracted from the flowers of a daisy-like member of the chrysanthemum group. Pyrethrins are compounds derived from pyrethrum. For similar synthetic insecticides see pyrethroids.

Pyrethrum/pyrethrins are used in many household insecticide sprays and aerosols. They are available as spray concentrates and dusts for use on vegetables, fruit trees, ornamentals and shrubs. They are used in some mosquito coils. Low volumes are sometimes used for large-scale treatment against flies and mosquitoes.

These chemicals are nerve poisons affecting the central and peripheral nervous systems of insects. The affected insects suffer excitation, paralysis and death. The synergist piperonyl butoxide is nearly always included in pyrethrin formulas to increase their effectiveness.

Health effects
The use of pyrethrum does not affect the health of most people or other mammals, however some people are sensitive to it. Piperonyl butoxide, which is commonly added to formulations, can also affect the immune system. Fruit and vegetables sprayed or dusted with it can be used immediately after harvesting but it is advisable to wash all fruit and vegetables before eating. Pyrethrum/pyrethrins are toxic to fish and it is important to cover aquariums when using them in the house.