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.

Why It Matters

Pesticide exposure can occur through household and personal care products as well as 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.

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.

Found In

Pesticides used on crops
Lice treatments
Pet flea shampoos
Bug-resistant clothing and outdoor gear
Bug repellents
Foggers

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.[13]

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

Consumers can read labels to identify and avoid relevant ingredients. 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. 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.

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.