Why It Matters
When most of us think of pesticides, we generally think of crops. However, pesticides can end up in our homes and bodies in ways beyond just food. Products like over-the-counter lice treatments, pet shampoos, gardening products, and bug sprays can all contain registered pesticides, too. This chemical profile contains information about a class of pesticides known as pyrethroids – how they can find their way into our homes and ways to minimize exposure.
What Is It?
Pyrethroids are a class of pesticides to which cyfluthrin, permethrin, and pyrethrins belong. They are often used in insect repellents or other bug-resistant gear and personal care products.
Permethrin is a pesticide most frequently used to treat bug-resistant clothing and outdoor gear, but it can also be found in bug sprays and other treatments. Though it’s a little more complicated than this, you can think of pyrethrins as the natural counterpart to permethrin. Pyrethrins are a mix of six chemicals found naturally in chrysanthemum flowers. They are typically extracted from the flower, but sometimes the whole, crushed flower is used, which is called pyrethrum powder.
Cyfluthrin is an insect repellent that structurally resembles the notorious chemical DDT and has a similar mode of action. Like DDT, it accumulates in fat tissues.
Insect repellents are regulated as pesticides in the United States because their active ingredients are pesticides. [15] The Environmental Protection Agency (EPA) reviews substances for their human and environmental harm prior to allowing them to be used as pesticides. However, pyrethroids and other pesticides are still allowed by the EPA despite evidence of toxicity to humans and the environment.
Where It's Found
Each of the three pyrethroids have similar uses.
Permethrin is most frequently used to treat bug-resistant clothing, mosquito netting and outdoor gear, though it’s also often used in bug sprays and very commonly used worldwide as a pesticide for crops. Pyrethrins, the natural counterpart to permethrin, are used in products meant to control bugs like household insecticides, foggers, sprays, dusts, and pet shampoos. [9] Pyrethrins are also used on crops. Both permethrin and pyrethrins are also used in over-the-counter lice treatments, as well as in flea shampoos and treatments for pets.
Cyfluthrin is used in bug sprays, wipes, clothing repellents, and in repellents for pets.
The Health Concern
Permethrin is a neurotoxin that acts on sodium ion channels, promoting repeated nerve impulses. [17] When permethrin is found at high levels, it can affect the function of chloride channels, which may result in seizures. [4] One study found that permethrin and DEET, either in combination or separately, were linked to the death of neural cells in various parts of the brain, which may lead to physiological and behavioral issues, including problems with motor skills, learning and memory. [1] Another study found that newborn exposure to permethrin impaired working memory by interfering with neural processing in the frontal lobe of the brain. [8]
Orally, permethrin was classified as a likely carcinogen by the EPA in 2009. [13] Since then, it has been reclassified according to the EPA’s Guidelines for Carcinogen Risk Assessment as having suggestive evidence of carcinogenic potential. [14] This means there is concern for potential carcinogenic effects to humans, however, the data is not sufficient to make a stronger claim. Permethrin is classified by the International Agency for Research on Cancer (IARC) as “not classifiable as to its carcinogenicity to humans”. More research is needed on carcinogenicity when exposed through the skin. Permethrin is toxic to fish, aquatic life, and bees. [9]
Just because pyrethrins are natural does not mean they are inherently safe. Pyrethrins and other pyrethroids have been linked to endocrine disrupting effects. [5] [6] [7] Pyrethrins may also be associated with the development of allergic sensitization , and if you’re allergic to ragweed, exposure can cause difficulty breathing or an asthmatic attack . [11] [16] In multiple cases , people’s exposure to pyrethrins and other pyrethroids through in-home use products like flea shampoos for pets has led to death. [10] Pyrethrins are also toxic to aquatic life and bees . [9]
Similar to permethrin, cyfluthrin is linked to neurotoxicity and interferes with sodium and potassium ion channels in the nerves; in animal studies, this results in loss of coordination, muscle trembling, behavior changes and more. [2] One study showed harmful effects of cyfluthrin on blood, including decreased glucose and red blood cells. Another study found that mice exposed to both high and low doses of cyfluthrin in the womb displayed significant behavior changes. [12] Normal liver function was also disrupted by cyfluthrin in studies on rats. [3] Cyfluthrin is harmful to aquatic invertebrates, fish, and honeybees. [2]
How to Avoid It
Read labels. Look for permethrin, pyrethrin, or cyfluthrin listed under “active ingredients” on bug repellent product labels.
Choose safer bug repellent options. Be aware that in addition to pyrethroids, there are other harmful ingredients in bug repellents. For tips on choosing safer bug repellent and control, check out our fact sheet and report . Look for plant-based alternatives with bug-repelling oils like citronella, clove, lemongrass, lemon eucalyptus, thyme and neem. Make sure to buy commercially prepared products or consult an essential oils specialist to ensure that all essential oils are properly diluted. Some people are sensitive to essential oils, so do a small patch test and consult an expert. Lastly, reduce your exposure to mosquitos by staying indoors when mosquitos are the worst (at dawn and dusk), covering up with thick fabrics and long plants and sleeves, and using mosquito netting.
Skip products containing both sunscreen and bug spray, as the mixture may increase your skin’s absorption of the chemicals.
Seek out nontoxic lice treatment and prevention products, as opposed to conventional over-the-counter products. Read our lice treatment and prevention guide to learn how to choose safer options.
When it’s time to give the dog a bath, use good old-fashioned shampoo, soap and water. Or try a gentle, all-purpose castile soap. There is no need to use flea shampoos when you’re not experiencing an infestation. If you need flea prevention or treatment, look for natural options as opposed to those containing pesticides. Some companies make pet-safe herbal shampoos intended to prevent fleas. You can even DIY your own flea sprays using pet-safe essential oils, but make sure to consult your vet about essential oil safety for your pet.
Use a welcome mat and take your shoes off when you enter your home. Pesticide residue can be tracked into the home through shoes worn outside.
Wash all fruits and vegetables thoroughly, including organic produce. Look for pesticide-free produce when possible. (Tip: check out the farmers’ market and ask what they use. Farmers love talking about their food!)
If you’re a gardener, give natural and organic methods a try to reduce your exposure to pesticides. Visit your local natural greenhouse for tips. There are numerous books and online guides available too.
Shop MADE SAFE Certified products. Pyrethroids are not permitted in our process.
Notes
*Essential oils and DIY bug repellents: Some botanicals can be irritating, so try a small patch test before use and avoid any known allergens. Always make sure to dilute essential oils properly and follow manufacturer guidelines. If you intend to use essential oils on your pet, make sure to consult your vet.
*Zika and other mosquito-borne illnesses: Knowing your area and if you are at risk for mosquito-borne or tick-borne illness can help you make the right bug repellent choice for you and your family. If you think you are at risk, heed the advice of the CDC, WHO, and your doctor.
*Efficacy of bug repellents: MADE SAFE does not test for efficacy. We examine ingredients for human health and environmental harm. Please refer to the company selling natural bug repellents for information regarding efficacy and usage.
References
[1] Abdel-Rahman, A., Shetty, A.K., Abou-Donia, M.B. (2001). Subchronic Dermal Application of N,N-Diehtyl m-Toluamide (DEET) and Permethrin to Adult Rats, Alone or in Combination, Causes Diffuse Neuronal Cell Death and Cytoskeletal Abnormalities in the Cerebral Cortex and the Hippocampus, and Purkinje Neuron Loss in the Cerebellum. Experimental Neurology. 172: 153-171. https://www.beyondpesticides.org/assets/media/documents/mosquito/documents/
[2] Beyond Pesticides. (2007). Cyfluthrin Fact Sheet. Retrieved from https://www.beyondpesticides.org/assets/media/documents/pesticides/factsheets/
[3] Bhushan, B., Saxena, P.N., Saxena, N. (2013). Biochemical and histological changes in rat liver caused by cypermethrin and beta-cyfluthrin. Archives of Industrial Hygiene and Toxicology. 64(1): 57-67. https://doi.org/10.2478/10004-1254-64-2013-2184
[4] Bradberry, S.M., Cage, S.A., Proudfoot, A.T., Vale, J.A. (2005). Poisoning due to pyrethroids. Critical Reviews in Toxicology. 24(2): 93-106. https://doi.org/10.2165/00139709-200524020-00003
[5] Brander, S.M., Gabler, M.K., Fowler, N.L., Connon, R.E., Schlenk, D. (2016). Pyrethroid Pesticides as Endocrine Disruptors: Molecular Mechanisms in Vertebrates with a Focus on Fishes. Envir. Sci. Technol. 50(17): 8977-8992. https://doi.org/10.1021/acs.est.6b02253
[6] Eil, C. and Nisula, B.C. (1990). The binding properties of pyrethroids to human skin fibroblast androgen receptors and to sex hormone binding globulin. Journal of Steroid Biochemistry. 35(3-4): 409-414. https://doi.org/10.1016/0022-4731(90)90248-Q
[7] Hurley, P.M., Hill, R.N., Whiting, R.J. (1998). Mode of Carcinogenic Action of Pesticides Inducing Thyroid Follicular Cell Tumors in Rodents. Environmental Health Perspectives. 106(8): 437-445. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1533205/pdf/envhper00531-0045.pdf
[8] Nasuti, C., Carloni, M., Fedeli, D., Gabbianelli, R., Di Stefano, A., Serafina, C.L., Silva, I., Domingues, V., Ciccocioppo, R. (2013). Effects of early life permethrin exposure on spatial working memory and on monoamine levels in different brain areas of pre-senescent rats. Toxicology. 303: 162-168. https://doi.org/10.1016/j.tox.2012.09.016
[9] National Pesticide Information Center. (2014). Pyrethrins General Fact Sheet. Retrieved from http://npic.orst.edu/factsheets/pyrethrins.pdf
[10] Pell, M.B. and Morris, J. (2008). ‘Safe’ pesticides now first in poisonings. The Center for Public Integrity. Accessed February 8, 2023. Retrieved from https://publicintegrity.org/workers-rights/safe-pesticides-now-first-in-poisonings/
[11] Solomon, G.M. (2003). Asthma and the Environment. School of Medicine, University of Calfornia, San Francisco and the Natural Resources Defense Council. Retrieved from https://www.healthandenvironment.org/docs/AsthmaReview2003.pdf
[12] Soni, I., Syed, F., Bhatnagar, P., Mathur, R. (2010). Perinatal toxicity of cyfluthrin in mice: Developmental and behavioral effects. Human and Experimental Toxicology. 30(8): 1096-1105. https://doi.org/10.1177/0960327110391386
[13] United States Environmental Protection Agency (EPA). (2009). Permethrin Facts. Retrieved from https://www3.epa.gov/pesticides/chem_search/reg_actions/reregistration/fs_PC-109701_1-Aug-09.pdf
[14] United States Environmental Protection Agency (EPA). (2020). Permethrin: Human Health Risk Assessment for New Use on “Fruit, Small, Vine Climbing, Except Fuzzy Kiwifruit, Subgroup 13-07F”; Multiple Crop Group Conversions/Expansions; and the Establishment of a Tolerance without a U.S. Registration for Tea, AND the Revised Draft Risk Assessment (DRA) for Registration Review. Retrieved from file:///C:/Users/jessi/Downloads/EPA-HQ-OPP-2011-0039-0130_content.pdf
[15] United States Environmental Protection Agency (EPA). (2017). What is an insect repellent? Retrieved from https://www.epa.gov/insect-repellents/what-insect-repellent
[16] U.S. Food & Drug Administration. (2022). CFR – Code of Federal Regulations Title 21. Accessed February 8, 2023. Retrieved from https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=358&showFR=1&subpartNode=21:5.0.1.1.30.7
[17] Wolansky, M.J. and Harrill, J.A. (2008). Neurobehavioral toxicology of pyrethroid insecticides in adult animals: a critical review. Neurotoxicol Teratol. 30(2): 55-78. https://doi.org/10.1016/j.ntt.2007.10.005
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