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PUBLIC HEALTH STATEMENT 

PYRETHRINS and PYRETHROIDS 

Division of Toxicology September 2003 

This Public Health Statement is the summary 

chapter from the Toxicological Profile for 

Pyrethrins and Pyrethroids. It is one in a series of 

Public Health Statements about hazardous 

substances and their health effects. A shorter 

version, the ToxFAQsTM, is also available. This 

information is important because this substance may 

harm you. The effects of exposure to any hazardous 

substance depend on the dose, the duration, how 

you are exposed, personal traits and habits, and 

whether other chemicals are present. For more 

information, call the ATSDR Information Center at 

1-888-422-8737. 

_____________________________________ 

This public health statement tells you about 

pyrethrins and pyrethroids and the effects of 

exposure. 

The Environmental Protection Agency (EPA) 

identifies the most serious hazardous waste sites in 

the nation. These sites make up the National 

Priorities List (NPL) and are the sites targeted for 

long-term federal cleanup activities. Pyrethrins and 

pyrethroids have been found in at least 5 and 2 of 

the 1,636 current or former NPL sites, respectively. 

However, the total number of NPL sites evaluated 

for these substances is not known. As more sites are 

evaluated, the sites at which pyrethrins and 

pyrethroids are found may increase. This 

information is important because exposure to these 

substances may harm you and because these sites 

may be sources of exposure. 

When a substance is released from a large area, 

such as an industrial plant, or from a container, such 

as a drum or bottle, it enters the environment. This 

release does not always lead to exposure. You are 

exposed to a substance only when you come in 

contact with it. You may be exposed by breathing, 

eating, or drinking the substance, or by skin contact. 

If you are exposed to pyrethrins and pyrethroids, 

many factors determine whether you'll be harmed. 

These factors include the dose (how much), the 

duration (how long), and how you come in contact 

with them. You must also consider the other 

chemicals you're exposed to and your age, sex, diet, 

family traits, lifestyle, and state of health. 

1.1 WHAT ARE PYRETHRINS AND 

PYRETHROIDS? 

Pyrethrum is a naturally occurring mixture of 

chemicals found in certain chrysanthemum flowers. 

Pyrethrum was first recognized as having 

insecticidal properties around 1800 in Asia and was 

used to kill ticks and various insects such as fleas 

and mosquitos. Six individual chemicals have active 

insecticidal properties in the pyrethrum extract, and 

these compounds are called pyrethrins. Pyrethrum 

looks like a tan-colored dust as ground flowers or a 

syrupy liquid as the crude extract. Pyrethrins are 

only slightly soluble in water, but they dissolve in 

organic solvents like alcohol, chlorinated 

hydrocarbons, and kerosene. Pyrethrins are often 

used in household insecticides and products to 

control insects on pets or livestock. Pyrethrins break 

down quickly in the environment, especially when 

exposed to natural sunlight. 

Pyrethroids are manufactured chemicals that are 

very similar in structure to the pyrethrins, but are 

often more toxic to insects, as well as to mammals, 

and last longer in the environment than pyrethrins. 

More than 1,000 synthetic pyrethroids have been 

developed, but less than a dozen of them are 

currently used in the United States. Pyrethrins and 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

PYRETHRINS and PYRETHROIDS 

Division of Toxicology September 2003 

pyrethroids are often combined commercially with 

other chemicals called synergists, which enhance 

the insecticidal activity of the pyrethrins and 

pyrethroids. The synergists prevent some enzymes 

from breaking down the pyrethrins and pyrethroids, 

thus increasing their toxicity. 

Most commercial pyrethroids are not one single 

molecule; rather, they are several molecules with 

the same chemical formula that have their atoms 

joined together in the same sequence, but have a 

different arrangement of the atoms in space. Such 

compounds are called stereoisomers. If the 

stereoisomers are not mirror images of one another, 

they are called diastereomers and have different 

physical properties like boiling point, melting point, 

and solubility. If they are nonsuperimposable mirror 

images of each other, they are called enantiomers 

and properties like boiling point, melting point, and 

solubility are identical. However, both 

diastereomers and enantiomers can have different 

insecticidal properties and different toxicities. Some 

pyrethroids are composed of as many as eight 

different stereoisomers. 

Technical-grade (concentrated) pyrethrins and 

pyrethroids are usually mixed with carriers or 

solvents to produce a commercial-grade formulated 

product. The formulated product contains many 

inert ingredients that can increase the toxicity of the 

product when compared to the technical-grade 

material. By law, the active ingredient must be 

identified by name on the pesticide label and its 

percentage must be provided. Nonactive ingredients 

(sometimes called inert ingredients) do not need to 

be identified by name on a pesticide label, only the 

percentage of nonactive ingredients must be 

specified, so it is often difficult to determine what 

other chemicals are included in the final formulated 

product. 

1.2 WHAT HAPPENS TO PYRETHRINS AND 

PYRETHROIDS WHEN THEY ENTER 

THE ENVIRONMENT? 

Pyrethrins and pyrethroids are primarily released to 

air because of their use as insecticides. Sometimes 

they are sprayed on crops from planes and 

helicopters or sprayed from the ground by trucks, 

tractors, or hand-held applicators. They are also 

used to control flying insects like mosquitos and 

flies on livestock and pets. These compounds are 

also in aerosol bombs and sprays that can be used 

indoors. Pyrethrins can be released naturally from 

chrysanthemum flowers, but these releases are 

small compared with the amounts used as 

commercial insecticides. Manufacturing facilities 

that produce these compounds can also release them 

to the environment during the production process. 

In air, all six of the pyrethrins and many of the 

pyrethroids are broken down or degraded rapidly by 

sunlight or other compounds found in the 

atmosphere. Often, they last only 1 or 2 days before 

being degraded. Rain and snow help remove the 

pyrethroids from air that are not rapidly degraded. 

Since many of these compounds are extremely toxic 

to fish, they are usually not sprayed directly onto 

water, but they can enter lakes, ponds, rivers, and 

streams from rainfall or runoff from agricultural 

fields. These compounds bind strongly to dirt and 

usually are not very mobile in soil. Pyrethrins and 

pyrethroids are not easily taken up by the roots of 

plants and vegetation because they are strongly 

bound to the soil; however, they are often sprayed 

directly onto crops and plants so they may be found 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

PYRETHRINS and PYRETHROIDS 

Division of Toxicology September 2003 

on leaves, fruits, and vegetables. Because these 

compounds adsorb so strongly to soil, pyrethrins 

and pyrethroids usually do not leach into 

groundwater, do not contaminate drinking water 

supplies, and volatilize from soil surfaces slowly. 

These compounds are eventually degraded by the 

microorganisms in soil and water. They can also be 

degraded by sunlight at the surfaces of water, soil, 

or plants. However, some of the more recently 

developed pyrethroids can persist in the 

environment for a few months before they are 

degraded. 

1.3 HOW MIGHT I BE EXPOSED TO 

PYRETHRINS AND PYRETHROIDS? 

You can be exposed to pyrethrins and pyrethroids in 

several ways. Eating foods that are contaminated 

with these compounds is the most likely way. You 

can also breathe in air that contains these 

compounds. This is especially possible soon after 

the insecticide has been sprayed. After spraying, 

these compounds can also come in contact with 

your skin and you can be exposed by dermal 

contact. These compounds are contained in many 

household insecticides, pet sprays, and shampoos. 

Some pyrethroids are also used as lice treatments 

that are applied directly to the head and as mosquito 

repellents that can be applied to your clothes. A 

common treatment for scabies is the application of a 

pyrethroid to the affected skin surface excluding the 

scalp. The use of these products can lead to 

exposure. 

The average daily intake of permethrin (the most 

frequently used pyrethroid in the United States) for 

a 70 kilogram adult male is estimated as about 3.2 

micrograms per day (1 microgram equals 

1/1,000,000 of a gram). This value is about 1,000 

times less than the acceptable daily intake (ADI) of 

permethrin derived by the United Nations' Food and 

Agriculture Organization (FAO) and the World 

Health Organization (WHO). 

1.4 HOW CAN PYRETHRINS AND 

PYRETHROIDS ENTER AND LEAVE MY 

BODY? 

Pyrethrins and pyrethroids usually enter the body 

when people eat foods contaminated by these 

chemicals. They may also enter your body by 

breathing air that contains these compounds or 

through dermal exposure when you use 

commercially available insecticides that contain 

pyrethrins and pyrethroids. These chemicals are 

absorbed by the body when you eat contaminated 

foods and breathe contaminated air, but they are not 

as easily absorbed through the skin when you touch 

contaminated soil, vegetation, or insecticides 

containing these compounds. Some insect repellents 

that are applied to the skin contain pyrethrins or 

pyrethroids in addition to another chemical called 

DEET, which may allow the pyrethrins or 

pyrethroids to enter your body more easily. 

Pyrethrins and pyrethroids can enter your body if 

you swallow drinking water contaminated with 

these compounds, but since pyrethrins and 

pyrethroids are rarely found in drinking water, this 

will be a minor exposure route. Accidental 

exposures to pyrethrins or pyrethroids may also 

occur if these pesticides are improperly used. 

Pyrethrins and pyrethroids that enter the body leave 

quickly, mainly in the urine, but also in feces and 

breath. These compounds are also quickly broken 

down by the body into other chemicals called 

metabolites. The concentration of these chemicals 

in the urine increases as the amount of the exposure 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

PYRETHRINS and PYRETHROIDS 

Division of Toxicology September 2003 

goes up. If exposure levels are very high or if 

exposure occurs over a long time, then pyrethrins 

and pyrethroids can build up in fatty tissue and 

remain in the body for a little longer. Certain types 

of pyrethroids can also be retained for longer 

periods of time in the skin and hair. 

1.5 HOW CAN PYRETHRINS AND 

PYRETHROIDS AFFECT MY HEALTH? 

Pyrethrins and pyrethroids interfere with the way 

that the nerves and brain function. If you get a large 

amount of pyrethrins or pyrethroids on your skin, 

you may get feelings of numbness, itching, burning, 

stinging, tingling, or warmth that could last for a 

few hours. You are not likely to be exposed to 

amounts of pyrethrins or pyrethroids by breathing 

air, eating food, or touching anything that would 

cause enough pyrethrins or pyrethroids to enter your 

body and cause other problems. But if very large 

amounts of these chemicals were to enter your 

body, you might experience dizziness, headache, 

and nausea that might last for several hours. Larger 

amounts might cause muscle twitching, reduced 

energy, and changes in awareness. Even larger 

amounts could cause convulsions and loss of 

consciousness that could last for several days. 

Allergic reactions have been seen in a few 

individuals who used products that contain 

pyrethrins or pyrethroids. There is no evidence that 

pyrethrins or pyrethroids cause birth defects in 

humans or affect the ability of humans to produce 

children. There is evidence from animal studies that 

pyrethrins and pyrethroids might be capable of 

causing cancer in people, but the evidence comes 

from animals that ate very large amounts of 

pyrethrins or pyrethroids for a lifetime. 

To protect the public from the harmful effects of 

toxic chemicals and to find ways to treat people 

who have been harmed, scientists use many tests. 

One way to see if a chemical will hurt people is to 

learn how the chemical is absorbed, used, and 

released by the body; for some chemicals, animal 

testing may be necessary. Animal testing may also 

be used to identify health effects such as cancer or 

birth defects. Without laboratory animals, scientists 

would lose a basic method to get information 

needed to make wise decisions to protect public 

health. Scientists have the responsibility to treat 

research animals with care and compassion. Laws 

today protect the welfare of research animals, and 

scientists must comply with strict animal care 

guidelines. 

Animal studies show effects of pyrethrins and 

pyrethroids similar to those seen in people exposed 

to very high amounts of these chemicals. In 

addition, exposure to pyrethrins or pyrethroids 

might affect the ability of some animals to 

reproduce and may also cause cancer. 

1.6 HOW CAN PYRETHRINS AND 

PYRETHROIDS AFFECT CHILDREN? 

This section discusses potential health effects from 

exposures during the period from conception to 

maturity at 18 years of age in humans. 

Children exposed to large amounts of pyrethrins or 

pyrethroids would be expected to be affected in the 

same manner as adults. If children were to get a 

large amount of pyrethrins or pyrethroids on their 

skin, they might get feelings of numbness, itching, 

burning, tingling, or warmth that could last for a 

few hours. If very large amounts of these chemicals 

were to enter a child's body, the child might 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

PYRETHRINS and PYRETHROIDS 

Division of Toxicology September 2003 

experience dizziness, headache, and nausea that 

might last for several hours. Even larger amounts 

could cause muscle twitches, tremors, convulsions, 

and loss of consciousness that could last up to 

several days. 

Pyrethroids might be able to penetrate the skin of 

infants and young children more easily than the skin 

of adults. Infants and young children are more 

easily dehydrated than adults through exercise, flue, 

colds, and the conditions that contribute to fluid 

loss. Therefore, pyrethroids that penetrate the skin 

may become more concentrated in internal tissues 

of the young. 

There is no evidence in humans that pyrethrins or 

pyrethroids cause birth defects. Some young 

animals showed signs of possible damage to the 

body's defense system that fights infection after 

their mothers were exposed to pyrethroids while 

their babies were developing in the womb. There is 

some indication that the developing brain of some 

very young animals could be affected by 

pyrethroids. 

1.7 HOW CAN FAMILIES REDUCE THE 

RISK OF EXPOSURE TO PYRETHRINS 

AND PYRETHROIDS? 

If your doctor finds that you have been exposed to 

significant amounts of pyrethrins or pyrethroids, ask 

whether your children might also be exposed. Your 

doctor might need to ask your state health 

department to investigate. 

Pyrethrins and pyrethroids are effective insecticides 

that are often used in household sprays, aerosol 

bombs, insect repellents, pet shampoos, and lice 

treatments. Using products containing these 

compounds will expose you to these chemicals. If 

you decide to use these products, carefully follow 

the instructions on how to apply them properly and 

how long to wait before re-entering the treated area. 

Do not apply more than the recommended amount. 

Pesticides and household chemicals should be 

stored out of reach of young children to prevent 

accidental poisoning. Always store pesticides in 

their original labeled containers; never store 

pesticides in containers that young children would 

find attractive, such as old soda bottles. If you feel 

sick after a pesticide has been used in your home, 

call the local poison control center or see a doctor. 

Keep your poison control center's number next to 

the phone. If a close neighbor or someone living 

nearby is applying pyrethrins or pyrethroids, you 

may want to remain indoors with your children and 

pets in order to avoid being accidentally exposed to 

these chemicals. Certain pyrethroids, such as 

permethrin, phenothrin, and resmethrin, are sprayed 

to control mosquitos during the spring and summer. 

Remaining indoors and closing your windows while 

your neighborhood is being sprayed will lessen your 

exposure. 

Since these compounds frequently are used on 

crops, they are often detected in fruits and 

vegetables. Make sure you wash fruits and 

vegetables thoroughly before eating them. Trim the 

fat from meat and poultry because pesticides often 

concentrate in fat. These compounds are often 

detected in soils, especially in agricultural areas. 

Some children eat a lot of dirt. You should 

discourage your children from eating dirt. Make 

sure they wash their hands frequently and before 

eating. Discourage your children from putting their 

hands in their mouths or any other hand-to-mouth 

activity. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

PYRETHRINS and PYRETHROIDS 

Division of Toxicology September 2003 

1.8 IS THERE A MEDICAL TEST TO 

DETERMINE WHETHER I HAVE BEEN 

EXPOSED TO PYRETHRINS AND 

PYRETHROIDS? 

Methods exist that can detect pyrethrins and 

pyrethroids in blood and urine. Because these 

compounds are broken down in the body quickly, 

there are also ways to measure the metabolites of 

these chemicals in human blood and urine. These 

methods are not available in a doctor's office 

because special equipment is required. However, a 

sample taken in a doctor's office can be shipped to a 

special medical laboratory, if necessary. These 

laboratories are usually located at research 

universities or affiliated with government agencies 

such as the Centers for Disease Control and 

Prevention (CDC). Your doctor may need to contact 

the county health department for a list of 

laboratories that can perform these tests. Because 

pyrethrins and pyrethroids break down in the body 

rapidly, these methods are useful only if exposure 

has occurred within the last few days. At this time, 

these methods can tell only if you have been 

exposed to pyrethrins or pyrethroids and cannot tell 

if you will have any adverse health effects. Methods 

also exist that can measure the concentration of 

pyrethrins and pyrethroids in air, water, soil, and 

foods. 

For pesticide emergencies, the National Pesticide 

Information Center (NPIC) (formerly called the 

National Pesticide Telecommunications Network 

[NPTN]) located at Oregon State University, is also 

available. The NPIC (telephone number: 1-800-858­

7378 for the general public and 1-800-858-7377 for 

medical profession/government agencies) provides 

information about pesticides to anyone in the 

United States. 

1.9 WHAT RECOMMENDATIONS HAS THE 

FEDERAL GOVERNMENT MADE TO 

PROTECT HUMAN HEALTH? 

The federal government develops regulations and 

recommendations to protect public health. 

Regulations can be enforced by law. Federal 

agencies that develop regulations for toxic 

substances include the Environmental Protection 

Agency (EPA), the Occupational Safety and Health 

Administration (OSHA), and the Food and Drug 

Administration (FDA). Recommendations provide 

valuable guidelines to protect public health but 

cannot be enforced by law. Federal organizations 

that develop recommendations for toxic substances 

include the Agency for Toxic Substances and 

Disease Registry (ATSDR) and the National 

Institute for Occupational Safety and Health 

(NIOSH). 

Regulations and recommendations can be expressed 

in not-to-exceed levels in air, water, soil, or food 

that are usually based on levels that affect animals; 

then they are adjusted to help protect people. 

Sometimes these not-to-exceed levels differ among 

federal organizations because of different exposure 

times (an 8-hour workday or a 24-hour day), the use 

of different animal studies, or other factors. 

Recommendations and regulations are also 

periodically updated as more information becomes 

available. For the most current information, check 

with the federal agency or organization that 

provides it. Some regulations and recommendations 

for pyrethrins and pyrethroids include the 

following: 

The WHO has recommended that the level of 

permethrin in drinking water not exceed 20 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov 
 

 

 

 

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PUBLIC HEALTH STATEMENT 

PYRETHRINS and PYRETHROIDS 

Division of Toxicology September 2003 

micrograms per liter (μg/L). OSHA regulates the 

level of pyrethrins in workplace air. The 

occupational exposure limits for an 8-hour 

workday, 40-hour workweek are 5 mg per cubic 

meter (mg/m3). The EPA has recommended daily 

oral exposure limits for 10 different pyrethroids. 

These limits range from 0.005 to 0.05 mg/kg/day. 

In September of 1997, the EPA issued a request to 

pesticide formulators to voluntarily change the term 

"inert ingredients" to "other ingredients" on 

pesticide labels because the general public often 

believed that inert ingredients meant harmless 

ingredients. Since federal law does not define inert 

ingredients on the basis of toxicity or hazard to 

humans, it should not be assumed that all inert 

ingredients are nontoxic. The EPA publishes a list 

of all inert ingredients used in currently registered 

pesticides, but it does not specify which ingredients 

are contained in any specific formulated product. 

1.10 WHERE CAN I GET MORE 

INFORMATION? 

If you have any more questions or concerns, please 

contact your community or state health or 

environmental quality department or: 

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, Mailstop F-32 

Atlanta, GA 30333 

Information line and technical assistance: 

Phone: 888-422-8737 

FAX: (770)-488-4178 

ATSDR can also tell you the location of 

occupational and environmental health clinics. 

These clinics specialize in recognizing, evaluating, 

and treating illnesses resulting from exposure to 

hazardous substances. 

To order toxicological profiles, contact: 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

Phone: 800-553-6847 or 703-605-6000 

Reference 

Agency for Toxic Substances and Disease Registry 

(ATSDR). 2003. Toxicological profile for 

pyrethrins and pyrethroids. Atlanta, GA: U.S. 

Department of Health and Human Services, Public 

Health Service. 

DEPARTMENT of HEALTH AND HUMAN SERVICES, Public Health Service
 

Agency for Toxic Substances and Disease Registry 

www.atsdr.cdc.gov/ Telephone: 1-888-422-8737 Fax: 770-488-4178 E-Mail: atsdric@cdc.gov