As of 2011, NPIC stopped creating technical pesticide fact sheets. The old collection of technical fact sheets will remain available in this archive, but they may contain out-of-date material. NPIC no longer has the capacity to consistently update them. To visit our general fact sheets, click here. For up-to-date technical fact sheets, please visit the Environmental Protection Agency’s webpage.
Molecular Structure -
Permethrin
Laboratory Testing: Before pesticides are registered by
the U.S. EPA, they must undergo laboratory testing for
short-term (acute) and long-term (chronic) health effects.
Laboratory animals are purposely given high enough doses
to cause toxic effects. These tests help scientists judge how
these chemicals might affect humans, domestic animals,
and wildlife in cases of overexposure.
- Permethrin is an insecticide in the pyrethroid chemical family. The International Union of Pure and Applied Chemistry
(IUPAC) name for permethrin is 3-phenoxybenzyl (1RS,3RS;1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethyl-cyclopropanecarboxylate
and the Chemical Abstracts Service (CAS) registry number is 52645-53-1.1 Permethrin is considered a type I pyrethroid.2
- Permethrin was originally registered for use by the United States
Environmental Protection Agency (U.S. EPA) in 1979, and it was
re-registered in 2006.3 See the text box on Laboratory Testing.
- Permethrin is a blend of two stereoisomers.1 Details on the ratio
used in a specific product may be listed on the label, or may not
be readily available. For the remainder of this fact sheet, note
that permethrin refers to an isomer blend and not one isomer alone.
- Technical permethrin ranges from a colorless crystal to a yellow or brown viscous
liquid.1,2 No information on the odor of permethrin was found.
- Vapor pressure2: 2.15 x 10-8 mmHg
- Octanol-Water Partition Coefficient (Kow)1: 6.1 at 20 °C
- Henry's constant2: 1.4 x 10-6 atm·m3/mol
- Molecular weight1: 391.3 g/mol
- Solubility (water)1,2: 5.5 x 10-3 mg/L, 6 x 10-3 mg/L
- Soil Sorption Coefficient (Koc)4: 1.00 x 105
- Permethrin can be used in public health mosquito abatement programs and
on a variety of food or feed crops and livestock; or in structures and buildings,
including livestock housing and food-handling establishments. Permethrin
can also be used in numerous residential sites, both indoor and outdoor, and on
pets and clothing. When permethrin is used on large areas like crops, nurseries,
and sod farms it is considered a restricted use pesticide. For other applications,
it is considered a general use pesiticide. Formulations of permethrin used for
treatment of head lice and scabies on humans are available, but these are considered pharmaceuticals, which are regulated
by the United States Food and Drug Administration (FDA).2 Uses for individual permethrin products vary widely. Always
read and follow the label when applying pesticide products.
- Signal words for products containing permethrin may range from Caution to Danger. The signal word reflects the combined
toxicity of the active ingredient and other ingredients in the product. See the pesticide label on the product and refer to
the NPIC fact sheets on Signal Words and Inert or "Other" Ingredients.
- To find a list of products containing permethrin which are registered in your state, visit the website
http://npic.orst.edu/reg/state_agencies.html select your state then click on the link for "State Products."
Target Organisms
- Permethrin acts on the nervous system of insects. It interferes with sodium channels to disrupt the function of neurons,
and causes muscles to spasm, culminating in paralysis and death.1,2
- Permethrin can be effective by contact or ingestion and also acts as a mild repellent.1
Non-target Organisms
- Permethrin is highly toxic to honeybees, fish, and aquatic invertebrates due to disruption of sodium channels.1,3,5
- In general, mammals are less susceptible to permethrin compared to insects because their sodium channels are less sensitive
to pyrethroids and recover more rapidly. Also, because of their larger body size and greater metabolic capabilities,
mammals are more likely to metabolize pyrethroids, such as permethrin, before they can affect the nervous system.5,6 Conversely,
cats can be sensitive to products with high concentrations of permethrin, possibly due to insufficient glucoronide
conjugation capability, which hinders the metabolism of permethrin.7,8
Oral
- In rat studies, permethrin LD50 values range from 430-4000 mg/
kg. Permethrin LD50 values for mice range from 540-2690 mg/
kg. Factors contributing to the variability of these values include
age, sex, carrier and isomer ratio.1
- The U.S. EPA considered permethrin to be low in toxicity for
acute oral exposure based on an acute oral LD50 range of 2280-
3580 mg/kg in rats.2 See the text boxes on Toxicity Classification and LD50/LC50.
LD50/LC50: A common
measure of acute toxicity is the lethal dose (LD50) or
lethal concentration (LC50) that causes death (resulting
from a single or limited exposure) in 50 percent of the treated
animals. LD50 is generally expressed as the dose in
milligrams (mg) of chemical per kilogram (kg) of body
weight. LC50 is often expressed as mg of chemical per
volume (e.g., liter (L)) of medium (i.e., air or water) the organism
is exposed to. Chemicals are considered highly toxic when the
LD50/LC50 is small and practically non-toxic
when the value is large. However, the LD50/LC50
does not reflect any effects from long-term exposure (i.e., cancer,
birth defects or reproductive toxicity) that may occur at levels below
those that cause death.
Dermal
- The dermal LD50 for permethrin in rabbits is over 2000 mg/kg. The U.S. EPA considered permethrin to be low in toxicity for
acute dermal expsoure.2,9
- Permethrin is considered to be low in toxicity for potential eye irritation and very low in toxicity for potential skin irritation.
All irritation in test rabbits cleared within 48 hours for dermal exposures and 72 hours for ocular exposures.2 Permethrin is
not considered a skin sensitizer.2,9
Inhalation
- One study found a 4-hour inhalation LC50 in rats greater than 23.5 mg/L.9 However, the U.S. EPA recognizes this area as a
"data gap" and is seeking acute inhalation toxicity data for permethrin.2
| TOXICITY CLASSIFICATION - PERMETHRIN |
|
High Toxicity |
Moderate Toxicity |
Low Toxicity |
Very Low Toxicity |
| Acute Oral LD50 |
Up to and including 50 mg/kg
(≤ 50 mg/kg) |
Greater than 50 through 500 mg/kg
(>50-500 mg/kg) |
Greater than 500 through 5000 mg/kg
(>500-5000 mg/kg) |
Greater than 5000 mg/kg
(>5000 mg/kg) |
| Inhalation LC50 |
Up to and including 0.05 mg/L
(≤0.05 mg/L) |
Greater than 0.05 through 0.5 mg/L
(>0.05-0.5 mg/L) |
Greater than 0.5 through 2.0 mg/L
(>0.5-2.0 mg/L) |
Greater than 2.0 mg/L
(>2.0 mg/L) |
| Dermal LD50 |
Up to and including 200 mg/kg
(≤200 mg/kg) |
Greater than 200 through 2000 mg/kg
(>200-2000 mg/kg) |
Greater than 2000 through 5000 mg/kg
(>2000-5000 mg/kg) |
Greater than 5000 mg/kg
(>5000 mg/kg) |
| Primary Eye Irritation |
Corrosive (irreversible destruction of
ocular tissue) or corneal involvement or
irritation persisting for more than 21 days |
Corneal involvement or other
eye irritation clearing in 8 -
21 days |
Corneal involvement or other
eye irritation clearing in 7
days or less |
Minimal effects clearing in less than 24 hours |
| Primary Skin Irritation |
Corrosive (tissue destruction into the
dermis and/or scarring) |
Severe irritation at 72 hours
(severe erythema or edema) |
Moderate irritation at 72
hours (moderate erythema) |
Mild or slight irritation at
72 hours (no irritation or
erythema) |
| The highlighted boxes reflect the values in the "Acute Toxicity" section of this fact sheet. Modeled after the U.S. Environmental Protection Agency, Office of Pesticide Programs, Label Review Manual, Chapter 7: Precautionary Labeling. https://www.epa.gov/sites/default/files/2018-04/documents/chap-07-mar-2018.pdf |
Signs of Toxicity - Animals
- Dermal exposures to cats and dogs may cause temporary paresthesia and neurological signs as evidenced by paw flicking
or ear, tail or skin twitching, or rolling on the ground.5
- Cats exposed dermally to some permethrin products may experience hyperexcitability, depression, ataxia, vomiting, anorexia,
tremors, or convulsions. Symptoms can begin within a few minutes or up to three days after the exposure. Some
permethrin products contain high concentrations of the active ingredient and are labeled for use only on dogs. Close
physical contact with a recently treated dog may also lead to symptoms in cats. If symptoms are severe and untreated, they
may result in death.5,7,10
- A report of 11 cats intentionally treated with products containing 45-65% permethrin described adverse effects including
muscle tremors, seizures, incoordination and agitation after exposure. Of the 11 cats that were treated, all were hospitalized,
and four died after the exposure. Seizures were found to develop within 24 hours of exposure, with some cats experiencing
seizures within two hours. In one additional case, a cat was in proximity of two large dogs treated with a permethrin
product 48 hours after treatment. Between 18 and 24 hours after being near the dogs, the cat developed signs including
agitation, tremors, seizures, and ataxia.11
- Animals may also display drooling or lip-smacking. This is believed to be a result of licking at the application site and
thought to be caused either by the taste or a tingling sensation in the mouth.5
- Cattle which have been treated topically with permethrin may show signs of paresthesia including twitching the skin on
their backs, trying to rub their backs, and general restlessness.5
Signs of Toxicity - Humans
- Dermal exposure to permethrin may cause irritation, itching, or paresthesia (a tingly, prickly sensation) at the site of contact.
These symptoms rarely last more than 24 hours.12 Ocular exposures may result in pain, redness, or a burning sensation.13
- While pyrethroids have been suggested as potential skin sensitizers,12 no human data were found to support this for permethrin.
- Ingestion of permethrin may cause sore throat, abdominal pain, nausea, and vomiting.6,13
- Inhalation of permethrin may cause headache, nasal and respiratory irritation, difficulty breathing, dizziness, nausea or
vomiting.6,13 Because of permethrin's low vapor pressure, inhalation exposures are more likely to result from aerosols, spray
droplets, and dust, than from actual vapors.6
- Always follow label instructions and take steps to minimize exposure. If any exposure occurs, be sure to follow the First Aid
instructions on the product label carefully. For additional treatment advice, contact the Poison Control Center at 1-800-
222-1222. If you wish to discuss an incident with the National Pesticide Information Center, please call 1-800-858-7378.
Animals
- Dogs fed daily doses of permethrin at 0, 5, 50 or 500 mg/kg body weight
per day for at least 96 days showed transient signs of permethrin toxicosis
at the highest dose used, including tremors. Researchers determined
the NOAEL to be 50 mg/kg per day for this study, based on
increased liver weights and neurological effects.9 See the text box on
NOAEL, NOEL, LOAEL, and LOEL.
NOAEL: No Observable Adverse Effect Level
NOEL: No Observed Effect Level
LOAEL: Lowest Observable Adverse Effect Level
LOEL: Lowest Observed Effect Level
- Mice were fed permethrin at concentrations ranging from 28 to 1400 mg/kg body weight per day for 28 days. No mice died
during this experiment and no significant clinical signs were seen. Necropsies revealed an increase in liver weights relative
to body weights in the 280 and 1400 dose groups. Researchers determined the NOAEL at 140 mg/kg per day based on the
doses used in this study.9
- Rabbits given 21 daily dermal doses of permethrin ranging from 0.10 to 1.0 g/kg body weight showed signs of skin irritation,
but no additional signs of toxicity were observed.14
- Guinea pigs, dogs, and rats were exposed to aerosolized permethrin for 13 weeks, five days per week, six hours each day.
Concentration levels used in the experiment were 125, 250, and 500 mg/m3. At the highest dose tested, rats experienced
tremors and convulsions in the first week only. The guinea pigs and dogs exhibited no clinical signs of poisoning throughout
the experiment.14
- Rats involved in a 2-year feeding study were given 100 mg/kg permethrin in their diet. These rats showed no signs of toxicity.1
Humans
- The U.S. EPA has determined a reference dose (RfD) and a Population Adjusted Dose (PAD) of 0.25 mg/kg/day for both
acute and chronic dietary exposures to permethrin. These levels are based on a NOAEL of 25 mg/kg/day in rats and an
Uncertainty Factor (UF) of 100.2 See the text box on Reference Dose (RfD).
- No human data were found on chronic effects of permethrin. See the text box on Exposure.
Exposure: Effects of permethrin on human health and the environment depend on how much
permethrin is present and the length and frequency of exposure. Effects also depend on the health
of a person and/or certain environmental factors.
- Experiments with rat and human cancer cell lines indicated that permethrin did not act as an antagonist for estrogens or
androgens, nor did it act as an agonist for estrogens or androgens.15,16 It was also concluded that permethrin did not act as a progestin in human cancer cells.15,16
However, other research on human cancer cell lines implied a potential for permethrin
to interfere with estrogenic activity through interface with the progesterone receptor.17 More research is required
to better understand any possible link between permethrin and endocrine function.
- Permethrin is included in the draft list of initial chemicals for screening under the U.S. EPA Endocrine Disruptor Screening
Program (EDSP). The list of chemicals was generated based upon exposure potential, not based on whether the pesticide
is a known or likely potential cause of endocrine effects.18
Animals
- Rats fed diets containing 500, 1000, or 2500 ppm for a period of two years showed no signs of carcinogenicity, however,
signs of toxicity were noted at the highest doses used.19
- A lifetime cancer study involving mice fed diets with 250, 1000, or 2500 ppm permethrin resulted in slightly elevated numbers
of benign hepatic tumors in males at the highest dose tested although the effect was not statistically significantly
different from controls.19
Humans
- In 1991, the International Agency for Research on Cancer (IARC) classified permethrin as Group 3, "not classifiable as to its
carcinogenicity to humans", due to a lack of evidence.20 More recently, the U.S. EPA has classified permethrin as "likely to
be carcinogenic to humans" by ingestion. This rating is based on benign lung and liver tumors found in mice and similar,
though inconclusive, evidence in rats, as well as corroborative Structure-Activity Relationships (SAR) information.2 See the text box on Cancer.
Cancer: Government agencies in the United States and abroad have developed programs to evaluate the
potential for a chemical to cause cancer. Testing guidelines and classification systems vary. To learn more
about the meaning of various cancer classification descriptors listed in this fact sheet, please visit the
appropriate reference, or call NPIC.
- No human data were found on the carcinogenic effects of permethrin.
Animals
- Researchers studied the potential developmental effects of oral exposure to permethrin in pregnant rats. At a dose of 150
mg/kg body weight per day of pregnancy, researchers observed a reduction in fetal rat weights and a greater occurrence
of additional ribs in the developing fetuses. No adverse effects were noted at 50 mg/kg body weight per day, the next lowest
dose.21
- A similar study examined the effects of oral permethrin exposures on the offspring of pregnant rabbits. At 1200 mg/kg body
weight per day of gestation, rabbits exhibited a greater loss of developing fetuses and decreased ossification of hind- and
fore-limbs of the fetuses. No adverse effects were observed at the next lowest dose, 600 mg/kg body weight per day.21
Humans
- A study was conducted involving 196 women who had applied a single, full-body, dermal dose of 4% permethrin as a
scabies treatment during their second or third trimesters of pregnancy. Researchers found no evidence that exposure to
permethrin affected the outcome of the participants' pregnancies.22
- A study involving 113 women using a 1% permethrin head lice treatment during pregnancy found no indication that exposure
to permethrin affected the outcome of their pregnancies.23
Absorption
- Human case studies involving skin applications of permethrin indicated that about 0.5% of the applied dose was absorbed dermally.24
- Animal studies showed quick and substantial absorption of permethrin upon ingestion.9 In one study of rats, about 60% of
the orally administered dose was absorbed with an absorption half-life of less than one hour.25
- No information was found regarding absorption rates following inhalation of permethrin.
Distribution
- Feeding studies using rats indicated that permethrin was rapidly distributed throughout the body. Peak concentrations
measured in plasma, nerve tissue, liver, and kidneys occurred around four hours after ingestion. Levels found in nervous
tissues were generally higher compared with in plasma.25,26
- A human case study involving an intentional ingestion of permethrin showed a similar distribution pattern with a peak
permethrin concentration found in blood three to four hours after ingestion.27
Metabolism
- In animal feeding studies using rats, goats, cows, and hens, permethrin was metabolized quickly in the liver. Hydrolysis,
hydroxylation, oxidation, and conjugation are all involved in the process of metabolism.9,28
- While several metabolites of permethrin have been identified, permethrin itself is considered the only compound of toxicological significance.2,9
Excretion
- Permethrin and its metabolites are excreted primarily in the urine, but also in the feces.6,9
- In rats given oral doses of permethrin, the excretion half-life was measured at 12.3 hours for plasma and from 9 to 23 hours
for certain brain and nervous tissue, including the medulla oblongata.25
- Permethrin metabolites can be detected in urine or blood; however, most clinical laboratories do not offer these testing
services. The presence of a measurable amount of these metabolites in blood or urine does not mean that adverse health
effects would be expected. In addition, these chemicals are not exclusively the products of exposure to permethrin. Further
research is needed for scientists to better understand the relationship between the measured metabolites and the potential
for adverse health effects.26
- The National Health and Nutrition Examination Survey (NHANES) included testing for permethrin metabolites in urine
among 2539 Americans, ages 6 to 59. The relevant metabolites detected were cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane
carboxylic acid, and 3-phenoxybenzoic acid. These chemicals are also metabolites of other pyrethroids,
thus their presence does not necessarily imply exposure to permethrin. The results from the NHANES survey indicated an
average concentration of 0.321 μg/L of 3-phenoxybenzoic acid. The other permethrin metabolites were frequently below
the level of detection so that a valid average concentration could not be calculated.29
Soil
- The average half-life of permethrin in aerobic soils is 39.5 days, with a range from 11.6 to 113 days.30 See the text box on Half-life.
- Permethrin binds tightly to soil and is broken down primarily by microorganisms, but also by photolysis.30
The "half-life" is the time required for half of the
compound to break down in the environment.
1 half-life = 50% remaining
2 half-lives = 25% remaining
3 half-lives = 12% remaining
4 half-lives = 6% remaining
5 half-lives = 3% remaining
Half-lives can vary widely based on environmental
factors. The amount of chemical remaining after a
half-life will always depend on the amount of the
chemical originally applied. It should be noted that
some chemicals may degrade into compounds of
toxicological significance.
Water
- When permethrin enters an aquatic system, some is degraded by
sunlight while in the water column but the majority binds tightly to
the sediment.30,31
- In water, permethrin is broken down by photolysis into 3-phenoxybenxzyl
alcohol (PBA) and dichlorovinyl acid (DCVA).32 The average
half-life range for permethrin in the water column is about 19-27
hours, however permethrin adsorbed to sediments can persist more
than a year.30
- Permethrin is not likely to contaminate groundwater due to its low
water solubility and strong adsorption to soil.4,30
Air
- Permethrin has the potential to drift depending on application technique,
however it has a very low vapor pressure and is not expected to volatilize.30
Plants
- The half-life of permethrin on plant foliage varies depending on the species. The approximate range is from one to three weeks.14
- Scientists applied radio labeled permethrin to soil at a rate of 2 kg/hectare. Sugar beets, wheat, lettuce, and cotton seeds
were planted in the treated soil 30, 60, and 120 days after treatment. Radioactive residues in the edible portions of mature
plants were found at levels up to 0.86 μg/g in the 30-day series and 0.09 μg/g in the 120-day series.33 A closer look at the
sugar beet residues in the 30-day series indicated that the radioactivity was more likely from uptake of the metabolites
than of the parent compound.33
Indoor
- Permethrin was applied in a thin layer to an indoor surface beside a window and exposed to daylight. After 20 days, 60% of
the permethrin remained on the surface.14
Food Residue
- In the FDA's Total Diet Study of 2003, permethrin residues were detected in 3% of the 1039 food samples tested. The range
of permethrin levels found was 0.0008-4.7130 ppm.34
- In the 2006 United States Department of Agriculture (USDA) Pesticide Data Program (PDP) report on pesticide residues
in food crops, total permethrin levels were measured in 1726 food samples including bananas, collard greens, summer
squash, and watermelon. A total of 0.5% of these samples had detectable residues of permethrin ranging from 0.048-4.900
ppm. None of the detected levels exceeded their corresponding permethrin tolerances.35
- When testing for the cis- and trans-isomers separately, the USDA examined several additional crops, including broccoli,
cranberries, peaches, and spinach. Of the 8948 samples tested, 6.7% had detectable residues ranging from 0.004 to 5.30
ppm. Spinach samples alone accounted for 97% of the detected levels of permethrin.35
Birds
- Oral dose LD50s for chickens, mallard ducks, and Japanese quail are >3000, >9800, and >13,500 mg/kg body weight, respectively.1
- Permethrin is low in toxicity to birds.1 However, some aerosol spray formulations contain a propellant
that may pose a hazard to birds by inhalation.5
Fish and Aquatic Life
- Permethrin is highly toxic to marine/estuarine, freshwater fish and other aquatic organisms.3
- For rainbow trout (Oncorhynchus mykiss), the 96-hour LC50 is 2.5 μg/L and the 48-hour LC50 is 5.4 μg/L. The 48-hour LC50s for
bluegill sunfish (Lepomis macrochirus) and Daphnia are 1.8 μg/L and 0.6 μg/L respectively.1
- Research with freshwater amphipods indicates permethrin in aquatic sediments may inhibit growth of exposed invertebrates
at levels as low as 44-73 ng/g sediment.36
- In a sediment toxicity study, researchers found detectable levels of permethrin in 26 of 30 creek sediment samples in
California. All 30 samples were found to be toxic to Hyalella azteca, a local species of amphipod, at 15 °C. Several sediment
samples also included other pyrethroids and low levels of organophosphates and/or organochlorines. Researchers
concluded the main contributors to sediment toxicity in this study were bifenthrin, cypermethrin, cyfluthrin, and lambdacyhalothrin.37
Terrestrial Invertebrates
- Permethrin is highly toxic to invertebrates, including honey bees and other beneficial insects. The topical LC50
for honeybees is 0.029 μg/bee.1,3
- The U.S. EPA has determined a RfD of 0.25 mg/kg/day
for both acute and chronic dietary exposures to permethrin.2 See the text box on Reference Dose (RfD).
- The U.S. EPA has classified permethrin as "likely to be carcinogenic to humans".2 See the text box on Cancer.
Reference Dose (RfD): The RfD is an estimate of the quantity of
chemical that a person could be exposed to every day for the rest
of their life with no appreciable risk of adverse health effects. The
reference dose is typically measured in milligrams (mg) of chemical
per kilogram (kg) of body weight per day.
U.S. Environmental Protection Agency, Integrated Risk Information System, IRIS Glossary, 2009. https://www.epa.gov/iris/iris-glossary#r
- The U.S. EPA has not determined a MCL for permethrin in drinking water. However, a limit of 0.3 mg/L was set by the World
Health Organization (WHO) as a guideline for permethrin in drinking water when it is applied to water for mosquito control.38
See the text box on Maximum Contaminant Level (MCL).
Maximum Contaminant Level (MCL): The MCL is the highest
level of contaminant that is legally allowed in drinking water.
The MCL is enforceable. The MCL is typically measured in
milligrams (mg) of contaminant per liter (L) of water.
U.S. Environmental Protection Agency, National Primary Drinking Water Regulations. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#one
- The Agency for Toxic Substances and Disease Registry (ATSDR)
determined Minimum Risk Levels (MRLs) for oral exposures to
technical grade permethrin of 0.3 mg/kg/day for acute oral
exposures (up to 14 days) and 0.2 mg/kg/day for intermediate
durations (15-364 days).26
Date Reviewed: March 2009
Please cite as: Toynton, K.; Luukinen, B.; Buhl, K.; Stone, D. 2009. Permethirn Technical Fact Sheet; National Pesticide Information
Center, Oregon State University Extension Services. http://npic.orst.edu/factsheets/archive/Permtech.html.
