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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 increase in use, 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.

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Registration Review of Pyrethrins and Pyrethroids

Ecological Risk Assessments and Risk Management Rationale

In late 2016, EPA 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. 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.

Human Health Risk Assessments

The draft human health risk assessments were conducted for each pyrethroid individually because each chemical has unique uses and hazard characteristics, which lead to different exposures and result in varying risks. These risk assessments were released in 2016, 2017 and 2018. 

Current Status

EPA is now evaluating comments received on the human health and ecological risk assessments and will release a proposed interim decision for each pyrethroid in late 2019. Interim decisions for each pyrethroid are anticipated to be released in 2020. 

Docket Numbers

Listed below are the docket numbers for each pyrethroid chemical. In each docket, you can view the human health risk assessment, the ecological assessment for 8 pyrethroids and the pyrethrins, and the ecological risk management rationale. The chemicals notated with a single asterisk (*) are included in the ecological risk assessment; the chemicals notated with a double asterisk (**) are covered by the ecological risk management rationale document. Other supporting registration review documents are also available in the dockets.

List of Pyrethrins, Pyrethroids and Synergists

Chemical Docket Number Status
Allethrins EPA-HQ-OPP-2010-0022 Interim decision (12/24/14)
*Bifenthrin EPA-HQ-OPP-2010-0384 Draft ecological assessment (11/29/16)
Draft human health risk assessment (12/15/17)
*Cyfluthrin  and beta-cyfluthrin EPA-HQ-OPP-2010-0684 Draft ecological assessment (11/29/16)
Draft human health risk assessment (12/15/17)
*Cypermethrin (alpha and zeta) EPA-HQ-OPP-2012-0167 Draft ecological assessment (11/29/16)
Draft human health risk assessment (2/28/18)
**Cyphenothrin EPA-HQ-OPP-2009-0842 Draft ecological assessment (11/29/16)
Draft human health risk assessment
(5/25/17)
**d-phenothrin EPA-HQ-OPP-2011-0539 Draft ecological assessment (11/29/16)
Draft human health assessment (11/29/16)
*Deltamethrin EPA-HQ-OPP-2009-0637 Draft ecological assessment (11/29/16)
Draft human health risk assessment (8/03/17)
 *Esfenvalerate EPA-HQ-OPP-2009-0301 Draft ecological assessment (11/29/16)
Draft human health risk assessment (8/03/17)
**Etofenprox EPA-HQ-OPP-2007-0804 Draft ecological assessment (11/29/16)
Draft human health risk assessment (9/13/17)
*Fenpropathrin EPA-HQ-OPP-2010-0422 Draft ecological assessment (11/29/16)
Draft human health assessment (11/29/16)
**Flumethrin EPA-HQ-OPP-2016-0031 Draft ecological assessment (11/29/16)
Draft human health risk assessment (5/24/18)
*Gamma-cyhalothrin EPA-HQ-OPP-2010-0479 Draft ecological assessment (11/29/16)
Draft human health risk assessment (9/13/17)
**Imiprothrin EPA-HQ-OPP-2011-0692 Draft ecological assessment (11/29/16)
Draft human health assessment (11/29/16)
*Lambda-cyhalothrin EPA-HQ-OPP-2010-0480 Draft ecological assessment (11/29/16)
Draft human health risk assessment (9/13/17)
Piperonyl butoxide (synergist) EPA-HQ-OPP-2010-0498 Draft ecological assessment (12/18/17)
Draft human health risk assessment (12/18/17)
**Momfluorothrin EPA-HQ-OPP-2015-0752 Draft ecological assessment (11/29/16)
Draft human health assessment (11/29/16)
*Permethrin EPA-HQ-OPP-2011-0039 Draft ecological assessment (11/29/16)
Draft human health risk assessment (9/13/17)
**Prallethrin EPA-HQ-OPP-2011-1009 Draft ecological assessment (11/29/16)
Draft human health assessment (11/29/16)
*Pyrethrins EPA-HQ-OPP-2011-0885 Draft ecological assessment (11/29/16)
Draft human health risk assessment (9/13/17)
**Resmethrin EPA-HQ-OPP-2010-0306 Ingredient canceled
**Tau-fluvalinate EPA-HQ-OPP-2010-0915 Draft ecological assessment (11/29/16)
Draft human health assessment (11/29/16)
**Tefluthrin EPA-HQ-OPP-2012-0501 Draft ecological assessment (11/29/16)
Draft human health assessment (11/29/16)
**Tetramethrin EPA-HQ-OPP-2011-0907 Draft ecological assessment (11/29/16)
Draft human health assessment (11/29/16)
Tralomethrin EPA-HQ-OPP-2012-0425 Registration review decision completed
**MGK-264 (synergist) EPA-HQ-OPP-2012-0415 Draft ecological assessment (11/29/16)
Draft human health assessment (11/29/16)

For more information:

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Previous Assessments

Reregistration - Ten of the pyrethrins, pyrethroids, and synergists were registered before Nov. 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. 

View a  summary of results of this assessment.   

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