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Fact Sheet: Review of the Relationship between Pyrethrins, Pyrethroid Exposure and Asthma and Allergies

Current as of June 2009

EPA has expedited a broad review of pyrethrins and pyrethroid incidents to identify any trends in the data. To determine whether there is an association between pyrethrins and pyrethroid products and asthma and allergy effects, EPA performed a thorough review of the animal and human data. The process of evaluation and the Agency’s conclusions are discussed in A Review of the Relationship between Pyrethrins, Pyrethroid Exposure and Asthma and Allergies (28 pp, 398k, About PDF) (US EPA, September 2009 corrected version).

This most recent review was prompted by a journal article titled ‘Safe’ Pesticides Now First in Poisonings, published by the Center for Public Integrity. The article focuses on human incidents and exposure to pyrethroid and pyrethrins pesticide products. It raises issues related to increases in numbers of incidents related to pyrethrins and pyrethroids, as well the safety of these products for individuals with asthma or allergies.

On this page you will find:

Allergies and Asthma

Pyrethrins and Pyrethroids

More information on pyrethrins and pyrethroids.

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Pyrethrins Reregistration Stewardship Program

EPA completed the Reregistration Eligibility Decision (RED) for pyrethrins in 2006. During reregistration the Agency considered the potential association between pyrethrins products and allergy/asthma effects. As a condition of the Agency’s reregistration decision, EPA required the Pyrethrins Joint Venture (PJV) to:

The PJV program will be tracked by the Agency. An annual report submitted to the Agency will be required for at least 5 years.

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Weight of Evidence Approach

In the current review, EPA used a weight of evidence approach to determine whether an association exists between pyrethrins/pyrethroid exposure and asthma and allergies. The current review included data from both animals and humans. The Agency considered animal data regarding:

The Agency also considered human data including incident data from several sources and human epidemiology studies.

In the weight of evidence analysis, EPA considered consistency, reproducibility, temporal and dose concordance, and biological plausibility of the effects reported in each data set and across all data sets. Comparisons of health effects profiles were also conducted between pyrethrins/pyrethroid products and other insecticides when possible to determine whether exposure to this class of pesticides elicits a heightened or unique respiratory/dermal response compared to other insecticides.

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Animal Data

The animal data do not indicate that exposure to pyrethrins or pyrethroid products is associated with the development or exacerbation of asthma. Data indicate that pyrethrins/pyrethroids have low acute toxicity via oral, dermal and inhalation routes of exposure and are not skin sensitizers.

Human Incident Data

The pyrethrins/pyrethroid incident data do not consistently show an effects profile that would indicate respiratory effects to be significantly heightened or biologically different from other insecticides. If this relationship were strong, a clear and consistent pattern of effects reported across multiple human incident databases, with higher percentages of respiratory illnesses and dermal responses would be expected.

EPA considered incident data from the following databases:

From this analysis, EPA has drawn the following information:

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Human Study Data

Available human epidemiological data do not consistently show results/outcomes that indicate pyrethrins or pyrethroids cause allergic and/or asthmatic responses, nor do they provide robust evidence that pyrethrins/pyrethroids trigger an allergic and/or asthmatic response.

Overall, the existing data did not support a positive relationship between pyrethrins/pyrethroid products and asthma/allergy effects.

Note that the human studies EPA considered do not constitute "research involving intentional exposure of a human subject" under EPA's Rule for the Protection of Human Subjects.

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Weight of Evidence Conclusion

Unlike previous reviews, the current assessment utilized a weight-of-evidence approach, integrating both animal and human data, to determine whether a clear association exists between pyrethrins/pyrethroid exposure and asthma and allergies. This decision is predicated on the premise that an integrative assessment is more informative than what any single dataset or study could provide, and that fundamental biological mechanisms of disease outcome are concordant across species. Based on the current analyses, the Agency concluded there is no clear and consistent pattern of effects reported to indicate conclusively whether there is an association between pyrethrins/pyrethroid exposure and asthma and allergies.

Regulatory Conclusion

The Agency is not requiring additional warnings or label statements specific to asthmatics on pyrethroids and pyrethrins end-use products, nor is the Agency requiring additional data from pyrethroid registrants at this time. However, as discussed above, as a condition of reregistration the Agency required the PJV to institute a product stewardship program that involved a prospective in-depth follow-up of reported pyrethrins incident cases to clarify the issue of a possible correlation between pyrethrins pesticide product use and adverse health incidents.

The Agency will review the pyrethrins incident data as it is submitted. If the Agency identifies discrepancies or trends in the data that differ from the incident data considered in this review, the Agency will consider requiring additional or similar data from the pyrethroid registrants.

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