Pet Safety / Compounds / Flumethrin

Is Flumethrin safe for dogs and cats?

Low risk for pets

Flumethrin is FDA-approved and veterinarian-recommended for dogs via the Seresto collar — the combination of imidacloprid and flumethrin provides 8-month flea and tick protection through sustained-release polymer matrix technology. Dogs are tolerant of the sustained-release formulation; reported adverse events in dogs (hair loss at collar site, skin irritation) are typically from the physical collar rather than flumethrin toxicity. Oral ingestion of an entire collar by a large dog would expose them to a much higher dose — veterinary monitoring is warranted if ingestion occurs.

What is flumethrin?

The IUPAC name is [cyano-(4-fluoro-3-phenoxyphenyl)methyl] 3-[2-chloro-2-(4-chlorophenyl)ethenyl]-2,2-dimethylcyclopropane-1-carboxylate.

Also known as: [cyano-(4-fluoro-3-phenoxyphenyl)methyl] 3-[2-chloro-2-(4-chlorophenyl)ethenyl]-2,2-dimethylcyclopropane-1-carboxylate, Bayticol, Bayvarol, Flumetrin.

IUPAC name
[cyano-(4-fluoro-3-phenoxyphenyl)methyl] 3-[2-chloro-2-(4-chlorophenyl)ethenyl]-2,2-dimethylcyclopropane-1-carboxylate
CAS number
69770-45-2
Molecular formula
C28H22Cl2FNO3
Molecular weight
510.4 g/mol
SMILES
CC1(C(C1C(=O)OC(C#N)C2=CC(=C(C=C2)F)OC3=CC=CC=C3)C=C(C4=CC=C(C=C4)Cl)Cl)C
PubChem CID
91702

Risk for dogs

Low risk

Flumethrin is FDA-approved and veterinarian-recommended for dogs via the Seresto collar — the combination of imidacloprid and flumethrin provides 8-month flea and tick protection through sustained-release polymer matrix technology. Dogs are tolerant of the sustained-release formulation; reported adverse events in dogs (hair loss at collar site, skin irritation) are typically from the physical collar rather than flumethrin toxicity. Oral ingestion of an entire collar by a large dog would expose them to a much higher dose — veterinary monitoring is warranted if ingestion occurs.

Risk for cats

Extreme risk

Flumethrin is a type II pyrethroid with extreme feline toxicity via the sodium channel CS-syndrome mechanism. Critical risk scenarios: (1) Seresto collars placed on cats at too-high a dose or with inappropriate cat formulations — the Seresto collar is specifically formulated for dogs and cats at distinct concentrations; (2) cats in close contact with dogs wearing Seresto dog collars — grooming a collar-wearing dog or lying against a dog with a Seresto collar can transfer enough flumethrin to trigger CS-syndrome in cats; (3) livestock ectoparasiticide products (Bayticol, Butox) misapplied near cats or contaminating cat-accessible water/surfaces on farms. ASPCA APCC data consistently list flumethrin-containing products among pyrethroid toxicosis reports in cats. The Seresto collar specifically has been the subject of thousands of adverse event reports to the EPA, with cat deaths documented following improper cat exposure to dog-formulation collars. Emergency treatment: remove collar/contamination source immediately, bathe cat, methocarbamol (IV), cyproheptadine, thermoregulation, IV lipid emulsion for severe refractory cases.

Regulatory consensus

1 regulatory bodyhas classified Flumethrin.

AgencyYearClassificationNotes
WHO—Class II

Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.

Where pets encounter flumethrin

  • Industrial Facilities — Manufacturing plants, Chemical storage areas, Waste treatment sites
  • Occupational Environments — Factories, Warehouses, Transportation vehicles

Safer alternatives

Lower-risk approaches that achieve a similar outcome to Flumethrin:

  • Safer process chemistry; Green chemistry alternatives; Exposure controls
    Trade-offs: Requires R&D investment to redesign synthesis routes; may reduce yield or throughput initially; long-term benefits include reduced waste treatment costs, regulatory compliance, and worker safety; 12 Principles of Green Chemistry framework available.
    Relative cost: 1.2-2×

Frequently asked questions

Is flumethrin safe for pets?

Flumethrin is FDA-approved and veterinarian-recommended for dogs via the Seresto collar — the combination of imidacloprid and flumethrin provides 8-month flea and tick protection through sustained-release polymer matrix technology. Dogs are tolerant of the sustained-release formulation; reported adverse events in dogs (hair loss at collar site, skin irritation) are typically from the physical collar rather than flumethrin toxicity. Oral ingestion of an entire collar by a large dog would expose them to a much higher dose — veterinary monitoring is warranted if ingestion occurs.

What products contain flumethrin?

Flumethrin appears in: Manufacturing plants (Industrial facilities); Chemical storage areas (Industrial facilities); Factories (Occupational environments); Warehouses (Occupational environments).

See Flumethrin in the pets app

Look up products containing flumethrin, compare to alternatives, and explore the full data record.

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Sources (2)
  1. US EPA: Seresto Collar Incident Data Review — imidacloprid and flumethrin; adverse event reports; flea and tick collar; cat and dog toxicosis; aquatic risk; human dermal transfer; sustained-release polymer matrix; 8-month efficacy; FIFRA risk assessment (2021) (2021) — regulatory
  2. ASPCA Animal Poison Control Center: Pyrethroid Toxicosis in Cats and Dogs — type I vs type II CS/T syndromes; extreme cat sensitivity (sodium channel/UGT deficiency); bathing decontamination; methocarbamol tremor control; cyproheptadine; lipid emulsion severe cases (2023) (2023) — veterinary

Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →