How does Pyrethrum work?

The active chemicals, the pyrethrins, are toxic to insect nervous systems.

Are there safety concerns?

Pyrethrum, when less than two grams are applied to the skin, is possibly safe for most people. While pyrethrum has limited toxicity at low doses, it can cause some side effects such as headache, ringing of the ears, nausea, tingling of fingers and toes, breathing problems, and other symptoms of nerve toxicity. Some people might have allergic reactions to pyrethrum. People at the greatest risk of allergic reactions are those who are allergic to plants in the Asteraceae/Compositae family such as ragweed, chrysanthemums, marigolds, daisies, and many other herbs.

Do not use pyrethrum on children less than two years old.

Do not take pyrethrum if:
  • You are pregnant or breast-feeding.
  • You are allergic to ragweed, chrysanthemums, marigolds, daisies, and other related plants.
  • You have asthma.

Dosing considerations for Pyrethrum.

The following doses have been studied in scientific research:

  • For treating head lice and crab lice: An over-the-counter (OTC) product that combines pyrethrins (0.17% to 0.33%) and piperonyl butoxide (2% to 4%) is applied to the affected area and allowed to remain for at least 10 minutes. The product is then thoroughly washed off with warm water. Pyrethrins are extracted from pyrethrum, and kill lice by harming their nervous systems.

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