Permethrin is a very popular pesticide for a variety of applications today. The biggest benefit is a quick knockdown effect on pests that come into contact with it with good residual killing-power.
It is slightly repellent to most pests. You can treat clothing, camping gear, boots, even mammals like dogs and livestock to help keep harmful pests like ticks from biting. It’s one of the cheaper pesticides you can buy, but is highly toxic to aquatic animals and cats.
Most any pest including Ants, Armyworm, Bark Beetles, Bat Bugs, Bed Bugs, Bees, Beetles, Borers, Boxelder Bugs, Brown Dog Ticks, Carpenter Ants, Carpenter Bees, Carpet Beetles, Centipedes, Chinchbugs, Cockroaches, Crickets, Earwigs, Elm Leaf Beetles, Fire Ants, Firebrats, Fleas, Flies, Flour Beetles, Ground Beetles, Gypsy Moths, Indian, Larder Beetles, Leaf Beetles, Meal Moths, Millipedes, Mole Crickets, Pillbugs, Scorpions, Silverfish, Sod Webworm, Sowbugs, Spiders, Stinkbugs, Ticks, Wasps, and more.
- Spraying for outdoor pests where you want to quickly reduce the population like ticks, fleas, and carpenter bees.
- Treating your hiking gear or dog to help prevent tick bites.
Liquid concentrates, granules, dusts, aerosols, foggers.
- Bifenthrin for a longer lasting residual killing effect.
- Fipronil for targeting social insects like ants, termites, bed bugs, and cockroaches.
Permethrin is a synthetic insecticide designed to resemble the pyrethroid molecules naturally found in chrysanthemum flowers – chemicals that naturally repel many types of insects.
Permethrin is generally safe to use – as long as the instructions are followed specifically for each product. While permethrin is cheap and effective, it can be extremely toxic for cats, bees, and aquatic organisms.
This article covers everything you need to know about Permethrin – in our standardized format so you can easily compare different pesticides!
When Was Permethrin Created?
Permethrin was first synthesized by M. Elliot and A.W. Farnham in 1973. At this time, research had clearly indicated the effectiveness of pyrethroids. However, most known pyrethroids were very unstable when exposed to light.
These researchers took time to develop pyrethroids that were “photostable” (able to handle exposure to light). Permethrin was synthesized by these researchers and was found to be very effective and stable in sunlight. This made permethrin very valuable for insect control in agricultural applications.
What is Permethrin?
Permethrin is a synthetic chemical, designed to resemble the pyrethroid compounds found in chrysanthemum flowers. These flowers naturally kill and repel many insects due to the pyrethroids they produce.
Unlike natural pyrethroids that degrade very quickly when exposed to sunlight, synthetic permethrin can last a month or more in direct sunlight. This makes it a very valuable insecticide because it can be sprayed onto crops and will be effective for weeks under natural conditions.
Permethrin is used in a number of different ways. In some applications, it is used to treat clothing and mosquito nets – killing bugs as they contact the material. Other formulas that use permethrin are intended as sprays or topical treatments.
It is very important to note that permethrin can be sold at very high liquid concentrations with the intent that you dilute it further with water before applying. High concentrations of permethrin can be toxic to humans, domestic animals, and non-target species in nature.
Typically, labels will advise permethrin to be diluted to 1-4% before application.
Pyrethroid compounds are a group of chemicals commonly used as pesticides. While there are many pyrethroids in nature, most insecticide pyrethroids are actually synthetic compounds meant to mimic the action of natural pyrethroid compounds.
Permethrin is one of the oldest and most widely used of the synthetic pyrethroids – though it is slowly being replaced by more specific, less toxic compounds. That being said, the World Health Organization still considers permethrin an “essential medicine” because it is cheap, effective, and has few environmental consequences when used properly.
What Insects Does Permethrin Control?
Permethrin has been found to be effective against many unwanted insects:
- Sand Flies
However, permethrin is considered a “broad-spectrum” pesticide. Like most pyrethroid compounds, permethrin affects many different organisms – from bees to aquatic organisms. See our section on Toxicity for more information.
How Does Permethrin Work?
Pyrethroid compounds like permethrin work by negatively affecting the nervous system of insects. The permethrin binds to receptors on nerve cells, rendering them ineffective. At the organism level, this leads to convulsions, seizures, and eventually death. This pathway is not biting-insect specific. All insects will be affected, including bees, dragonflies, and other desirable or beneficial insects.
Common Uses for Permethrin
One of the most common uses for permethrin is as a fabric treatment to repel ticks, fleas, mosquitos, and other biting insects. Several militaries around the world treat soldier uniforms with permethrin to deter ticks and other biting insects in the field. A permethrin treatment on your socks, boots, and pants can effectively kill any ticks that jump onto you!
Permethrin is also a common component in flea and tick prevention for dogs. It is found in the formulas for several flea-and-tick collars, as well as some topical creams and solutions to kill infestations. See the section below on why you should avoid permethrin if you have cats!
For humans, permethrin is typically used only as a clothing protectant – though there are two situations where it may be prescribed by a doctor. Head lice and scabies (an invasive skin mite) can both be treated by topical applications of permethrin. These are typically prescribed by a doctor and are very effective in treating lice and mite infestations.
Permethrin is certainly effective at killing and repelling a number of insects – though studies on its biological and environmental toxicities show that it does have detrimental effects on many “non-target” organisms including fish, crustaceans, bees, and cats.
For most mammals, permethrin is safe and effective when used at the dosage recommended by manufacturers. Permethrin is successfully used on many forms of livestock, as well as dogs and humans.
However, the one exception to this rule seem to be cats. Cats do not produce the enzyme needed to break permethrin down in the body, leading to very high levels of permethrin that cannot be destroyed. In cats, permethrin exposure can lead to seizures, muscle spasms, and even death if it is not treated by a doctor.
Most cat poisonings come from improper application of permethrin compounds intended for large dogs. So, if your cat has fleas, make sure you buy a cat-specific product that does not contain permethrin. Other cats get sick when exposed to residual permethrin leftover from a bug-bomb or spray treatment. Permethrin poising in cats is treatable, though some cats may need to spend up to 2 days in the vet’s care!
Permethrin is unfortunately very toxic to aquatic species – particularly crustaceans. Crustaceans and insects are closely related, so the fact that permethrin is highly toxic to both groups is not surprising. One study found that most crustaceans and aquatic insects were negatively impacted by even the tiniest amounts of permethrin in the water.
However, permethrin does not easily distribute in water. In fact, nearly 1.4 million pounds of permethrin are used every year and only 12% of USGS water samples contained any traces of permethrin. Of these samples, only a few had permethrin levels high enough to affect aquatic organisms. When used as a clothing treatment, permethrin sticks to the fabric and only a tiny amount is shed when the fabric contacts water.
Permethrin has not been shown to negatively affect birds. However, users should be cautious to avoid killing non-target species – the main diet of many birds.
Unfortunately, permethrin is very toxic to bees. Like ticks, mosquitos, and other insects, permethrin affects a bee’s brain – creating spasms, seizures, and eventually leading to death.
Permethrin should not be used on flowers or in places that bees frequent. Permethrin does break down in the soil over time, so long-term bee damage may be avoided if it is used only infrequently and never on flowers or plants that bees get food from.
There is data that shows permethrin caused lung and liver tumors in mice fed high levels of the insecticide. From the data, the EPA has issued a potential carcinogen warning, though permethrin is still approved as an insecticide on many edible crops.
With the standard applications of permethrin on clothing, as a spray, or as cream-based lice and mite solution, the levels of permethrin are far lower than levels that cause cancer in mice. Though permethrin appears on the WHO’s “safe and effective” medicines list, more research is needed into its carcinogenic effects.
Permethrin Study Summaries
Since its creation in 1973, permethrin has gone through a wide variety of health, safety, and efficacy studies. In general, permethrin is safe and very effective. Most tests indicate that permethrin has a 100% kill rate of fleas and ticks when applied following manufacturer instructions. But, let’s look at some other interesting permethrin studies:
Malaria is a terrible vector-borne disease, killing hundreds of thousands of people every year! One study found that by treating mosquito nets with permethrin, the child mortality rate in an area with excessive malaria was decreased by 25%.
While this may seem like a small number, it is actually very powerful. Many mosquito bites happen while we sleep, and a permethrin-treated netting was able to kill most mosquitos that contacted it. Coupled with skin-based repellents such as DEET, this may be an effective way to reduce malaria in many tropical locations.
Permethrin with Other Compounds
While permethrin on its own is effective in some applications, several studies have found that permethrin is more effective when used in combination with another insecticide or repellent.
One study showed that the most effective use of permethrin was as a clothing treatment. When subjects wore DEET-based repellents on their skin and permethrin-treated clothing, insect bites from mosquitos and ticks were reduced to near-zero! Certain application methods allow permethrin to stay in the clothing for up to 70 wash cycles – roughly the entire lifetime of most pieces of clothing.
Studies on fleas and ticks in dogs found that fipronil and permethrin together were 100% effective in treating flea infestations and removing ticks – even after the treated animals were bathed with soap! This also suggests that permethrin will stay affective even after rain, so you won’t need to reapply permethrin every time there is a light drizzle.
Affect on the Environment
Unfortunately, permethrin is not environmentally friendly. While the product does break down in the soil after a short time, permethrin is known to affect many non-target species including some mammals, many insects, and many aquatic organisms.
Specifically, permethrin is as effective at killing mayflies as it is at killing ticks and fleas. Many other aquatic insects and crustaceans – from dragonfly larvae to crawdads – will also likely be killed by even small amounts of permethrin. Since many of these animals serve as part of the base of the food chain, removing or killing them may affect the food supply for an entire ecosystem.
While the safety and efficacy of permethrin have been studied quite well, much more research is needed to effectively determine how to limit the environmental damage caused by permethrin.
Is Permethrin Banned by Any Countries?
Because of its potential as a carcinogen, its off-target effects, and its potential to cause environmental disruption, permethrin has been banned in many countries.
Permethrin is specifically banned in Canada and the European Union, and many other countries have followed their lead. In many countries, the product is not specifically banned – but, it is not currently approved for any uses.
In the United States, permethrin is still used and accepted as a form of insect control in a wide variety of applications. The EPA has noted permethrin’s potential carcinogenicity as well as the potential environmental destruction it could cause. The EPA decided to allowed permethrin based on the fact that it is typically applied at very low levels. Users should still exercise extreme caution when using and applying permethrin – as it can have very negative effects on a number of organisms.