Pyrethrins and Pyrethroids

This page includes information on the use of pyrethrins and pyrethroids as insecticides, the current reevaluation of this group of pesticides in registration review, and previous assessments, decisions, and risk mitigation efforts.

On this page:

What are pyrethrins and pyrethroids?

Pyrethrins and pyrethroids are insecticides included in over 3,500 registered products, many of which are used widely in and around households, including on pets and in treated clothing, in mosquito control, and in agriculture. The use of pyrethrins and pyrethroids has increased during the past decade with the declining use of organophosphate pesticides, which are more acutely toxic to birds and mammals than the pyrethroids.

This change to less acutely toxic pesticides, while generally beneficial, has introduced certain new issues. For example, residential uses of pyrethrins and pyrethroids may result in urban runoff, potentially exposing aquatic life to harmful levels in water and sediment.

Pyrethrins are botanical insecticides derived from chrysanthemum flowers most commonly found in Australia and Africa. They work by altering nerve function, which causes paralysis in target insect pests, eventually resulting in death.

Pyrethroids are synthetic chemical insecticides whose chemical structures are adapted from the chemical structures of the pyrethrins and act in a similar manner to pyrethrins. Pyrethroids are modified to increase their stability in sunlight

Most pyrethrins and some pyrethroid products are formulated with synergists, such as piperonyl butoxide and MGK-264, to enhance the pesticidal properties of the product. These synergists have no pesticidal effects of their own but enhance the effectiveness of other chemicals.

See the list of pyrethrins, pyrethroids and synergists.

Top of Page

Registration Review of Pyrethrins and Pyrethroids

EPA has released a draft ecological risk assessment for eight pyrethroids plus the pyrethrins and a risk management rationale for the remaining pyrethroids currently undergoing registration review. These documents are available at See the Federal Register notice in the docket for a list of the pyrethroid and pyrethrin dockets where these documents will be available for public comment. The comment period will be open until January 30, 2017. While the comment period is open, find links to the open dockets on our Open for Comment page.

The following chemicals are included in the ecological assessment (*) and the related risk management rationale (**):

Chemical Docket Number
*Bifenthrin EPA-HQ-OPP-2010-0384
*Cyfluthrins (and beta) EPA-HQ-OPP-2010-0684
*Cypermethrin (alpha and zeta) EPA-HQ-OPP-2012-0167
**Cyphenothrin EPA-HQ-OPP-2009-0842
*Deltamethrin EPA-HQ-OPP-2009-0637
**d-phenothrin EPA-HQ-OPP-2011-0539
*Esfenvalerate EPA-HQ-OPP-2009-0301
**Etofenprox EPA-HQ-OPP-2007-0804
*Fenpropathrin EPA-HQ-OPP-2010-0422
**Flumethrin EPA-HQ-OPP-2016-0031
*Gamma-cyhalothrin EPA-HQ-OPP-2010-0479
**Imiprothrin EPA-HQ-OPP-2011-0692
*Lambda-cyhalothrin EPA-HQ-OPP-2010-0480
**Momfluorothrin EPA-HQ-OPP-2015-0752
**Prallethrin EPA-HQ-OPP-2011-1009
*Permethrin EPA-HQ-OPP-2011-0039
*Pyrethrins EPA-HQ-OPP-2011-0885
**Tau-fluvalinate EPA-HQ-OPP-2010-0915
**Tefluthrin EPA-HQ-OPP-2012-0501
**Tetramethrin EPA-HQ-OPP-2011-0907

We assessed the pyrethroids and pyrethrins as a class rather than by individual chemical for our draft ecological risk assessment to increase efficiency and consistency in our assessments and to allow us to consider the risks and benefits of each insecticide compared to the others. 

The draft human health risk assessments will be completed individually because each chemical has unique uses and hazard characteristics. These factors lead to different exposures and result in varying risks. These assessments will be completed over the next year and will be provided for public comment as soon as they are available. View information about data requirements for human health assessment for the pyrethrins and pyrethroids.

Human health assessments for the following chemicals are included in this release:

Chemical Docket Number
d-phenothrin EPA-HQ-OPP-2011-0539
Fenpropathrin EPA-HQ-OPP-2010-0422
Imiprothrin EPA-HQ-OPP-2011-0692
Momfluorothrin EPA-HQ-OPP-2015-0752
Prallethrin EPA-HQ-OPP-2011-1009
Tau-fluvalinate EPA-HQ-OPP-2010-0915
Tefluthrin EPA-HQ-OPP-2012-0501
Tetramethrin EPA-HQ-OPP-2011-0907

Because many of the pyrethroids were registered after November 1984, they were not subject to reevaluation under the reregistration program. Since they may be used as alternatives for one another, we decided to assess and manage the risks of pyrethrins, pyrethroids and synergists in a similar time frame. Using this approach, we can ensure that risk assessment and risk management approaches are consistent within this class of pesticides.

For more information:

Top of Page

Previous Assessments

Reregistration - Ten of the pyrethrins, pyrethroids, and synergists were registered before November 1, 1984, and therefore were subject to reregistration. In 2008, EPA completed those Reregistration Eligibility Decisions (REDs). Read more about reregistration of the pyrethrins and pyrethroids

Cumulative Risk Assessment – EPA determined that pyrethrins and pyrethroids share a common mechanism of action for consideration in a cumulative risk assessment. The October 2011 Pyrethrins/Pyrethroid Cumulative Risk Assessment indicates that exposures from the many current uses of pyrethrins and pyrethroid insecticides do not pose risk concerns for children or adults. 

This screening-level cumulative risk assessment is highly conservative, overestimating actual risk. That is, the assessment assumes that people are exposed to the highest levels of residues in food, water, and in their homes, all on the same day. Even with these conservative and protective assumptions, the assessment shows that cumulative risks for both children and adults are not of concern for the currently registered uses of pyrethrins/pyrethroid pesticides. Further, the assessment shows that there is sufficient room in the pyrethroid cumulative risk cup to support consideration of additional individual pyrethroid pesticide uses.

View the pyrethrins/pyrethroid cumulative risk assessment.

Allergy and Asthma Assessment - In response to concerns expressed in a July 2008 Center for Public Integrity (CPI) journal article, EPA expedited its most recent review of available animal and human studies and human incident data to determine whether a clear association exists between exposure to pyrethrins and pyrethroid products and asthma and allergy effects. Agency scientists have concluded that there does not appear to be a clear relationship between pyrethrins/pyrethroid exposure and asthma/allergies. The Agency will continue to evaluate new data on this issue as it becomes available.

List of Pyrethrins, Pyrethroids and Synergists

Chemical Docket Number Status
Pyrethrins EPA-HQ-OPP-2011-0885 Draft ecological assessment (11/29/16)
Allethrin stereoisomers    
Bifenthrin EPA-HQ-OPP-2010-0384 Draft ecological assessment (11/29/16)
Cyfluthrin and beta-cyfluthrin EPA-HQ-OPP-2010-0684 Draft ecological assessment (11/29/16)
Cypermethrin (alpha and zeta) EPA-HQ-OPP-2012-0167 Draft ecological assessment (11/29/16)
Cyphenothrin EPA-HQ-OPP-2009-0842 Draft ecological assessment (11/29/16)
d-phenothrin EPA-HQ-OPP-2011-0539 Draft human health assessment (11/29/16)
Draft ecological assessment (11/29/16)
Deltamethrin EPA-HQ-OPP-2009-0637 Draft ecological assessment (11/29/16)
Esfenvalerate EPA-HQ-OPP-2009-0301 Draft ecological assessment (11/29/16)
Etofenprox EPA-HQ-OPP-2007-0804 Draft ecological assessment (11/29/16)
Fenpropathrin EPA-HQ-OPP-2010-0422 Draft human health assessment (11/29/16)
Draft ecological assessment (11/29/16)
Flumethrin EPA-HQ-OPP-2016-0031 Draft ecological assessment (11/29/16)
Gamma-cyhalothrin EPA-HQ-OPP-2010-0479 Draft ecological assessment (11/29/16)
Imiprothrin EPA-HQ-OPP-2011-0692 Draft human health assessment (11/29/16)
Draft ecological assessment (11/29/16)
Lambda-cyhalothrin EPA-HQ-OPP-2010-0480 Draft ecological assessment (11/29/16)
Momfluorothrin EPA-HQ-OPP-2015-0752 Draft human health assessment (11/29/16)
Draft ecological assessment (11/29/16)
Permethrin EPA-HQ-OPP-2011-0039 Draft ecological assessment (11/29/16)
1RS cis-permethrin    
Prallethrin EPA-HQ-OPP-2011-1009 Draft human health assessment (11/29/16)
Draft ecological assessment (11/29/16)
Resmethrin EPA-HQ-OPP-2010-0306 Ingredient canceled
Tau-fluvalinate EPA-HQ-OPP-2010-0915 Draft human health assessment (11/29/16)
Draft ecological assessment (11/29/16)
Tefluthrin EPA-HQ-OPP-2012-0501 Draft human health assessment (11/29/16)
Draft ecological assessment (11/29/16)
Tetramethrin EPA-HQ-OPP-2011-0907 Draft human health assessment (11/29/16)
Draft ecological assessment (11/29/16)
Tralomethrin EPA-HQ-OPP-2012-0425 Registration review decision completed
MGK-264 (synergist) EPA-HQ-OPP-2012-0415 Draft human health assessment (11/29/16)
Draft ecological assessment (11/29/16)
Piperonyl butoxide (synergist)    

Top of Page