Smarter Living: Chemical Index
These natural bug-killing chemicals, extracted from chrysanthemum flowers, can be less harmful to humans than other pesticides but depending on how they are used, can pose risks to ecosystems, pets, and people.
What Are They?
Pyrethrins are naturally occurring insect-killing chemicals taken from chrysanthemum flowers. In the flowers, these bug-killers exist as a mixture of six separate chemicals that together are called pyrethrum or pyrethrins.
Collected from flowers grown on large farms in central Africa and Australia, the chemicals are packaged for use in household bug sprays, houseplant and garden sprays, lice shampoos, and flea and tick treatments. In these products, pyrethrins are often combined with other chemicals that make them stick around longer and also increase their toxicity. One of these enhancers, piperonyl butoxide, is a possible human carcinogen according to the US Environmental Protection Agency (EPA).
Pyrethrins (without piperonyl butoxide or other enhancers) are permitted for use on organically grown crops.
Pyrethrins are often confused with their synthetic cousins, the pyrethroids. These synthetic versions, which include permethrin, cypermethrin, and others, are generally more toxic and longer lasting in the environment. For more information, see the Chemical Index entry on pyrethroids.
The chemicals kill by jamming communication between nerve cells, a system that works similarly in insects and mammals, like people and pets. As a result, pyrethrins can kill both pest insects and beneficial insects such as bees. When used by themselves, pyrethrins breakdown fairly quickly in the environment and can also be readily detoxified by most mammals. However, pyrethrins do pose a risk to cats because they lack the ability to process these chemicals and exposures can can cause tremors, twitching, convulsions, and death.
Pyrethrins, especially when used in combination with chemical enhancers such as piperonyl butoxide, can be toxic to the human nervous system as well and can also cause allergic reactions and exacerbate asthma.. EPA classifies pyrethrins as "Suggestive evidence of carcinogenicity but not sufficient to assess human carcinogenic
potential." Signs of pyrethin poisoning may include coughing, wheezing, shortness of breath, runny or stuffy nose, chest pain or difficulty breathing.
Several household bug-killing sprays, foggers, houseplant sprays, lice shampoos, and pet flea/tick control products contain pyrethrins, usually in combination with other chemicals. Using these products can expose you and your family.
Although pyrethrins break down quickly in sunlight, indoors they can persist in carpet dust for up to two months. When chemicals are present in floor and carpet dust, young children may ingest the chemicals after putting their hands in their mouths.
Eating conventional produce may expose you to pyrethrins, since commercial growers may use products with other chemicals that make them last longer and therefore leave a residue. When used on organic produce, pyrethrins break down within one to two days in sunlight and therefore are unlikely to leave a residue on food.
Although pyrethrins are less toxic than other pesticides, they should always be used with caution and only when non-chemical options are not available.
When it comes to pets, you can find less toxic treatments and chemical-free care at NRDC's GreenPaws Flea and Tick Products Directory. Use a flea comb to remove fleas and use pesticides as a last resort. With any pesticide, it’s important to read package labels, follow instructions, and use the least amount possible. Although cats are susceptible to pyrethrins, the chemicals are still used in cat treatments, so read labels before purchase.
Address roach and other pest, problems using integrated pest management (IPM) practices, which include promptly cleaning up food crumbs that attract insects, blocking entryways into your home, and using pesticides only when other methods have been exhausted. If you need professional help to safely eliminate household pests, refer to GreenShield and GreenPro for companies that use IPM methods.
Wash all fruits and vegetables before eating them, whether they are organic or not. If you're on a budget, choose organic where it matters most — see "Avoiding Toxic Produce" at OnEarth.
For information on removing lice, see NRDC’s "Our Children At Risk."
Find information about pyrethrins and their chemical cousins, the synthetic and more toxic pyrethroids, at the Agency for Toxic Substances and Disease Registry (ATSDR)'s Toxicological Profile for Pyrethrins and Pyrethroids.
Look up products to see if they contain pyrethrins at the National Institutes of Health’s Household Product Database.
last revised 12/27/2011