Summary from
Journal of Pesticide Reform, Spring 2002, Vol 22, No. 1

For the whole article, see listing of PYRETHRINS/PYRETHRUM 2002
on the web page at . Look under under Pesticide Fact Sheets.

Pyrethrins and pyrethrum are the most frequently used home and garden insecticides in the U.S. They are often used in indoor sprays, pet shampoos, and aerosol bombs to kill flying and jumping insects.

Pyrethrins are a common cause of insecticide poisonings. According to a U.S. Environmental Protection Agency (EPA) survey of poison control centers, they cause more insecticide poisoning incidents than any other class of insecticides except the organophosphates. Symptoms include headaches, dizziness, and difficulty breathing.

Pyrethrins can trigger life-threatening allergic responses including heart failure and severe asthma.

In laboratory animals exposed through eating, by injection, or through breathing, pyrethrins have caused anemia.

Experiments with dairy cows suggest that nursing mothers exposed to pyrethrins can pass them on to their children. Pyrethrins disrupt the normal functioning of sex hormones. They inhibit binding of sex hormones to human genital skin and proteins in human blood.

Pyrethrins are classified as "likely to be human carcinogens" by EPA because they cause thyroid tumors in laboratory tests. Farmers who use pyrethrins have an increased risk of developing leukemia.

Pyrethrins are extremely toxic to bees, fish, and other aquatic animals.

Following indoor treatments, pyrethrins have persisted up to 2 1/2 months in carpet dust.

A 2006 paper by David E. Rayan and Jeffrey R. Fry raises some new concerns. See A reassessment of the neurotoxicity of pyrethroid insecticides Pharmacology & Therapeutics Volume 111, Issue 1, July 2006, Pages 174-193. (The paper includes discussion of pyrethrins as well as pyrethroids.)