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Quick answer
Pyrethroids are a family of man-made insecticides modeled on pyrethrins, the natural insect-killing compounds in some chrysanthemum flowers, that act on an insect’s nervous system when it touches or eats them.
Bifenthrin, permethrin, cypermethrin and deltamethrin are common examples. They are among the most widely used pest control chemicals, but some bed bugs now resist them and they are highly toxic to fish and bees.
Quick facts
The key facts about Pyrethroids, with sources:
- How they work
- Disrupt sodium channels in insect nerve cells 4
- Common examples
- Bifenthrin, cypermethrin, deltamethrin, lambda-cyhalothrin, permethrin 5
- Fish and bees
- Bifenthrin is highly toxic to fish and very highly toxic to bees 3
- Cats
- Can be sensitive to high-concentration permethrin products 4
- Federal review
- EPA reviews the class together; page updated March 5, 2026 5
Key takeaways
- Pyrethroids are synthetic cousins of a flower-based insecticide, built to last longer than the natural version.
- They are used in perimeter sprays, termite soil treatments, bed bug products and many store-bought insect sprays.
- Some bed bug populations resist them, so a plan that relies only on pyrethroids can fail.
- They are much more toxic to insects, fish and bees than to people, and cats are especially sensitive to some permethrin products.
- California restricts how professionals may apply them outdoors to keep them out of storm drains and streams.
What pyrethroids are
Some chrysanthemum flowers make their own insecticide, called pyrethrins 2. Pyrethrins work fast but break down quickly in sunlight. Chemists built man-made versions that last longer. Those are pyrethroids. NPIC describes them simply as human-made versions of pyrethrins 3.
The family is large. The EPA’s registration review lists more than 20, including bifenthrin, cyfluthrin, cypermethrin, deltamethrin, esfenvalerate, lambda-cyhalothrin, permethrin and prallethrin 5. On a label, the active ingredient name usually ends in “-thrin.”
Pyrethroids are insecticides, not a brand. One chemical may be sold in many products and formulations: sprays, dusts, granules, aerosols and foggers 6.
How pyrethroids work on insects
Pyrethroids attack the nerves. The chain runs from first contact to death.
- Contact or feeding. The insect touches a treated surface or eats the chemical 3.
- Nerve disruption. The chemical interferes with sodium channels, the tiny gates that let nerve cells fire 4.
- Overexcitement. Nerves fire out of control, causing spasms 4.
- Paralysis and death. The insect stops moving and dies 4.
- Flushing. Pyrethrins and pyrethroids can also flush bed bugs out of hiding before killing them 6.
- ContactInsect touches or eats the treated surface
- Sodium channelsNerve gates are held open
- Nerves overfireMuscle spasms begin
- ParalysisThe insect stops moving
- DeathUnless the insect is resistant
Resistant bed bugs can survive this chain and simply move to a new hiding place. Source: [4] [6]
NPIC explains that bifenthrin is more toxic to insects than to people, partly because insects have smaller bodies and lower body temperatures 3.
Common pyrethroids and where you meet them
| Active ingredient | Where the sources mention it | Note |
|---|---|---|
| Bifenthrin | Homes and crops 3; termite liquids 7; bed bug products 8 | Binds tightly to soil 3 |
| Permethrin | Termite liquids 7; bed bug products 8 | A type I pyrethroid; cats are sensitive to high concentrations 4 |
| Cypermethrin | Termite liquids 7 | Also alpha- and zeta- forms 5 |
| Deltamethrin | Bed bug products 8 | Under EPA registration review 5 |
| Lambda-cyhalothrin | Bed bug products (as cyhalothrin) 8 | Under EPA registration review 5 |
| Pyrethrins (the natural parent) | Bed bug products 6 | Quick knockdown, little long-term control 8 |
Some bed bug products pair a pyrethroid with a neonicotinoid; UC IPM names two such mixtures 8.
Example: natural vs synthetic, by how long each lasts
This example compares published breakdown times for pyrethrins and one pyrethroid, permethrin. Conditions differ between the studies, so read the figures as a general contrast, not a side-by-side test.
| Chemical | Published half-life | What it means |
|---|---|---|
| Pyrethrins, on soil surfaces | 12.9 hours 2 | Half is gone in about half a day in sunlight |
| Pyrethrins, in water | 11.8 hours 2 | Breaks down fast in water with sunlight |
| Permethrin, in aerobic soil (average) | 39.5 days 4 | Lasts weeks, which is why it can keep working |
| Permethrin, in aerobic soil (range) | 11.6 to 113 days 4 | Soil and weather change the rate a lot |
The longer life is the point of a pyrethroid. It is also the reason runoff matters: a chemical that lasts on a driveway can be washed into a storm drain. NPIC’s permethrin figures come from a technical sheet last reviewed in March 2009 4.
Where you will see pyrethroids
On a product label. Look for a name ending in “-thrin” in the ingredient statement.
On a termite proposal. The EPA lists bifenthrin, cypermethrin and permethrin among common liquid termiticide ingredients 7. Our termite control page covers the options.
In a bed bug plan. Pyrethroids are one of the seven chemical classes registered for bed bugs 6.
In a perimeter service. Many recurring outdoor treatments use pyrethroids around foundations. Ask for the product name on your service ticket. See our recurring pest control page.
On pet products. Some dog flea and tick products contain permethrin; cats are sensitive to high concentrations 4.
Benefits and drawbacks
Why they are widely used
Limitations: resistance and repellency
Resistance is the biggest limit. The EPA says some bed bug populations have become resistant to pyrethrins and pyrethroids, and treatment may only move them to a new hiding place 6.
UC IPM says resistance among bed bugs is increasingly common, and some studies suggest pyrethroid mixtures may keep driving it 8. See pesticide resistance for how it develops.
Switching to a different chemical class is the main fix. The EPA says this can help control resistant bed bugs 6. That is why a good bed bug plan uses several methods, including heat treatment.
Natural pyrethrins add little lasting control. UC IPM says they give quick knockdown but little long-term control 8.
What drives cost, and how long protection lasts
We do not publish prices. Our standard needs many sourced, dated quotes for a dollar figure.
Pyrethroids are older chemistry, and many products contain them, so they are often the baseline choice in a service plan. Cost rises when resistance means adding another class, more visits or heat. For termites, Texas A&M testing found registered liquid termiticides last about four to ten years in soil 10.
How long a pyrethroid keeps working on a surface depends on the product, the surface, sun and rain. Our pest control cost guide and termite cost estimator show what drives a quote.
How professionals apply them responsibly
A licensed company should follow label rules and good practice on every pyrethroid job. Expect these steps.
- A label-based choice. The product label sets where and how it may be used. Ask for a copy, as the EPA advises for termite work 7.
- Targeted placement. California rules in effect since July 19, 2012 sharply limit how much pros spray outdoors, especially on concrete and other hard surfaces 9. Expect spot and crack-and-crevice work rather than broad spraying.
- No spraying in rain or over drains. California bans pro applications during rain, onto standing water and over drains 9.
- Rotation. For bed bugs, switching to a different chemical class helps with resistance 6.
- Re-entry. Ask when people and pets can return, as the label states. See re-entry intervals.
Keep cats away from dog products
Cats can be sensitive to high-concentration permethrin products, and NPIC lists hyperexcitability, tremors and seizures as signs 4. Never use a dog flea product on a cat. For a pet exposure, call your vet. When a person is exposed to a pyrethroid, call Poison Help at 1-800-222-1222, or 911 in an emergency.
After a treatment: what you can do
A few habits cut exposure and help the treatment work.
- Keep people and pets off treated areas until the label says it is safe.
- Do not hose treated driveways or patios into drains.
- Cover fish tanks and ponds, and tell the technician they are there; pyrethroids are highly toxic to fish 3.
- Tell the company about beehives or flowering plants nearby; bifenthrin is very highly toxic to bees 3.
- Report bugs that survive. Survivors may mean resistance, and the next round should change class 6.
Keep the ticket
Write down the product name and date of each treatment. If bugs keep surviving, your records help the technician pick a different chemical class.
Health and environmental risks
Skin tingling. Skin contact with bifenthrin can cause tingling, itching, burning or numbness, which usually clears within 48 hours 3. Breathing it in can irritate the nose, throat and lungs 3.
Pets. NPIC says dogs fed extremely large doses of pyrethrins drooled, trembled and lost coordination 2. Cats are sensitive to high-concentration permethrin 4.
Water and bees. Pyrethroids are highly toxic to fish and aquatic life and very highly toxic to bees 3. The EPA found risks of concern for invertebrates and fish 5.
Our pesticide safety guide covers storage and first aid, and pesticide poisoning explains warning signs.
Rules that apply to pyrethroids
Federal (EPA, FIFRA registration review). The EPA assesses pyrethroids and pyrethrins as a class.
Its late-2016 draft ecological risk assessments found potential risks for invertebrates and fish, and the EPA determined that measures to reduce spray drift and runoff are needed across the class.
Most chemicals in the class have an interim or proposed interim decision. The EPA page was last updated March 5, 2026 5.
California (DPR). On July 18, 2012, California’s Department of Pesticide Regulation announced rules on 17 pyrethroids, effective July 19, 2012. They limit outdoor use by professional pest control businesses and maintenance gardeners, especially on hard surfaces, and ban spraying during rain or over drains. They do not apply to individual consumers 9.
Labels. The label for each product sets where it may be used. States license the people who apply it; see pest control licensing.
Pyrethroids vs pyrethrins vs neonicotinoids
| Feature | Pyrethroids | Pyrethrins | Neonicotinoids |
|---|---|---|---|
| Origin | Man-made 3 | Chrysanthemum flowers 2 | Man-made to mimic nicotine 1 |
| Target in the insect | Sodium channels in nerves 4 | Excites the nervous system 2 | Insect nerve receptors; disrupts signals 1 |
| Lasting effect | Weeks in soil (permethrin average 39.5 days) 4 | Hours (12.9 hours on soil) 2 | Imidacloprid can last months or years in soil 1 |
| Bed bug resistance | Some populations resistant 6 | Some populations resistant 6 | Switching class can help with resistant bugs 6 |
| Fish | Highly toxic 3 | Highly to very highly toxic 2 | Imidacloprid slightly toxic, varies by species 1 |
Using a different class, such as a neonicotinoid or an insect growth regulator, is one way pros manage resistance.
Common misconceptions
- Myth Pyrethroids are natural because they come from flowers.
- Reality They are man-made versions of the flower compounds 3.
- Myth If it is plant-based, it is safe for fish and bees.
- Reality Natural pyrethrins are highly toxic to fish and honey bees 2.
- Myth A pyrethroid spray will clear bed bugs.
- Reality Some bed bugs resist pyrethroids and may just move to new hiding spots 6.
- Myth Pet flea products are interchangeable.
- Reality Cats can be sensitive to high-concentration permethrin products 4.
- Myth Spraying the driveway does no harm.
- Reality California sharply limits pro spraying on hard surfaces because runoff reaches waterways 9.
Where state rules change the picture
California is the clearest case. Since July 19, 2012, the Department of Pesticide Regulation has limited how professional pest control businesses apply 17 pyrethroids outdoors.
The rules target hard surfaces and drains because pyrethroids kept turning up in urban waterways at levels that can harm small aquatic organisms 9.
In practice, a California perimeter service looks different from one in many other states: more crack-and-crevice and band treatments, less spraying of driveways and walkways.
Other states set their own rules, so ask your provider what applies where you live.
When pyrethroids matter to you
Ask about pyrethroids when a company proposes a perimeter spray, a termite liquid or a bed bug treatment. Ask which product, where it goes and how they avoid drains, ponds and flowering plants.
If you have bed bugs that survived an earlier spray, ask the company to switch class or add heat 6. If you have cats, ask which products are used inside and keep cats away from treated dogs.
Compare plans from more than one licensed company. Our guide to choosing a pest control company lists what to ask.
Quick decision guide
If bed bugs survived a spray, ask for a different class or heat. With a pond, fish tank or hives nearby, tell the technician first. With cats at home, never use dog permethrin products on them. In California, expect targeted outdoor work instead of broad spraying.
Questions about Pyrethroids
What are pyrethroids used for?
Pyrethroids are insecticides used against many insects in homes, yards and crops. In pest control they appear in perimeter sprays, liquid termite treatments, bed bug products, mosquito treatments and many store-bought sprays. The EPA lists bifenthrin, cypermethrin and permethrin among common liquid termiticide ingredients.
Are pyrethroids safe for humans?
Pyrethroids are much more toxic to insects than to people, partly because insects are small and cold-bodied, NPIC says. They can still cause problems.
Skin contact with bifenthrin can cause tingling, itching or numbness that usually clears within 48 hours, and breathing it can irritate the airways.
Stick to the label, and after any exposure call Poison Help at 1-800-222-1222.
What is the difference between pyrethrins and pyrethroids?
Pyrethrins are natural insecticides found in some chrysanthemum flowers. Pyrethroids are man-made versions designed to act like them and last longer. Pyrethrins break down in hours in sunlight, while a pyrethroid like permethrin averages about 39.5 days in aerobic soil, according to NPIC.
Are pyrethroids safe for cats?
Cats need extra care. NPIC says cats can be sensitive to high-concentration permethrin products, possibly because they break it down poorly, and signs include hyperexcitability, tremors and seizures. Never put a dog flea or tick product on a cat. If a cat is exposed, call your vet right away.
Why don’t pyrethroids kill my bed bugs?
Some bed bug populations have become resistant to pyrethrins and pyrethroids, the EPA says, and treatment may only move them to a new hiding place. UC IPM says resistance is increasingly common. Switching to a different chemical class, using heat and combining methods are the usual fixes.
Are pyrethroids harmful to bees and fish?
Yes. NPIC says bifenthrin is highly toxic to fish and small aquatic organisms and very highly toxic to bees. Natural pyrethrins are also highly toxic to fish and honey bees. That is why labels restrict use near water and blooming plants, and why California limits outdoor professional use.
How long do pyrethroids last?
It depends on the chemical and conditions. NPIC reports permethrin’s average half-life in aerobic soil is 39.5 days, with a range of 11.6 to 113 days. Sun, rain and surface type change how long a treatment keeps working. For termites, Texas A&M found registered liquid termiticides last about four to ten years.
What are examples of pyrethroids?
Common examples are bifenthrin, cyfluthrin, cypermethrin, deltamethrin, esfenvalerate, lambda-cyhalothrin, permethrin and prallethrin. The EPA lists more than 20 pyrethroids in its registration review. Most names end in “-thrin,” which makes them easy to spot on a label.
Are pyrethroids banned?
No, pyrethroids are not banned in the United States. The EPA is reviewing them as a class and has found that drift and runoff controls are needed. California has restricted how professionals use 17 pyrethroids outdoors since July 19, 2012, mainly on hard surfaces and near drains.
Sources
- National Pesticide Information Center, Imidacloprid General Fact Sheet, retrieved .
- National Pesticide Information Center, Pyrethrins General Fact Sheet, retrieved .
- National Pesticide Information Center, Bifenthrin General Fact Sheet, retrieved .
- National Pesticide Information Center, Permethrin Technical Fact Sheet (archived; last reviewed March 2009), retrieved .
- U.S. EPA, Pyrethrins and Pyrethroids (registration review), last updated March 5, 2026, retrieved .
- U.S. EPA, Pesticides to Control Bed Bugs, retrieved .
- U.S. EPA, Termites: How to Identify and Control Them, retrieved .
- UC Statewide IPM Program, Pest Notes: Bed Bugs (Publication 7454), retrieved .
- California Department of Pesticide Regulation, news release: new restrictions to protect water quality in urban areas (July 18, 2012), retrieved .
- Texas A&M AgriLife Extension, Frequently Asked Questions About Subterranean Termite Control (ENT-2002), retrieved .
Expert review
Written by the HyrePest Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Definitions, mode of action, toxicity and half-lives are from NPIC fact sheets (the permethrin sheet is an archived technical sheet last reviewed March 2009, and is labeled as such).
The class list and review status are from the EPA page updated March 5, 2026. Bed bug resistance is from the EPA and UC IPM. California rules are from the DPR release of July 18, 2012.
Suggest a correction. We fix errors and say what changed.