Pyrethrum

Pyrethrum is the name of an extract obtained from the flowers of the plant Chrysanthemum cinerariifolium.

Pyrethrum should not be confused with pyrethrin. Pyrethrin is a more refined extract of pyrethrum. Pyrethrin is contained in some products against body lice. Pyrethrum is applied directly to the skin as an insecticide in the event of an infestation with lice or mites.

How does pyrethrum work?

The active chemicals, pyrethrins, are toxic to the nervous system of insects.

How effective is pyrethrum?

Pyrethrum is effective when used against lice. Applying pyrethrins to the skin in concentrations of 0.17 to 0.33% for 12 to 24 hours is effective in treating a lice infestation. Pyrethrins are usually combined with piperonyl butoxide (2% to 4%) to increase effectiveness. Pyrethrum is ineffective when used against mites.

Safety and side effects

Commercially available combinations of pyrethrins (0.17-0.33%) and piperonyl butoxide (2-4%) appear to be safe and harmless when applied to the skin. Pyrethrum may be safe and harmless when used on the skin in amounts less than 2 grams. Although pyrethrum has limited toxicity at low doses, it can cause some side effects such as headaches, tinnitus, nausea, tingling in fingers and toes, breathing problems and other central nervous system problems.

Precautions and warnings

Pregnancy and breastfeeding: Not enough is known about the use of pyrethrum during pregnancy and breastfeeding, so pregnant and breastfeeding women should avoid pyrethrum to be on the safe side.

Children: It is not safe to use pyrethrum on children under the age of two.

Asthma: Pyrethrin may aggravate asthma. For this reason, you should avoid pyrethrin products if you suffer from asthma.

Allergies to broomweed and related plants: The Chrysanthemum cinerariifolium flower or the pyrethrin extracted from it could cause allergic reactions in people who are sensitive to plants in the Asteraceae/Compositae family. Members of this plant family include broomweed, chrysanthemums, marigolds, daisies and many others. If you suffer from allergies, you should consult your doctor before using pyrethrum.

Interactions

At this time, there is no information on interactions of pyrethrum with medications or supplements.

Dosage

The following dosages have been investigated in scientific studies:

Applied to the skin

• To treat a lice infestation: Over-the-counter products combining pyrethrins (0.17% to 0.33%) and piperonyl butoxide (2% to 4%) are applied to the affected areas and left on for at least 10 minutes. The product is then washed off with warm water. Pyrethrins are extracted from pyrethrum and kill lice by damaging their nervous system.

References

1. Wagner SL. Fatal asthma in a child after use of an animal shampoo containing pyrethrin. West J Med 2000;173:86-7.