Is Permethrin toxic to cats?
No. Permethrin is a serious cat killer. It's the active ingredient in many dog flea spot-on treatments — applying a dog product to a cat, or a cat being near a recently treated dog, can cause severe poisoning.
If your cat has just eaten permethrin
- If permethrin is still on your cat's fur, wash with warm water and a mild dish soap (e.g. Fairy Liquid) to remove it — but only if your cat is still alert.
- If your cat is having tremors or seizures, go straight to the vet — do not delay for bathing.
- Call your vet immediately. Tell them specifically this is permethrin exposure — they will know this is a serious emergency.
- If you can't reach your vet, call Animal PoisonLine (01202 509000) — paid triage, 24/7.
What's the full picture?
Permethrin is safe for dogs at the doses used in their flea products but is highly toxic to cats. Cats can't metabolise pyrethroids the way dogs can. Applying a dog spot-on (e.g. some Bob Martin, some Beaphar, many supermarket own-brand products) to a cat is frequently fatal without treatment.
Exposure also happens when a cat grooms a dog who has recently had a spot-on applied, or sleeps on bedding contaminated with the product. Always separate cats and dogs for at least 72 hours after a dog spot-on.
Always check the label of any flea product you use — if it contains permethrin and is sold for dogs, it is not safe for cats to be near.
Permethrin toxicity from mis-applied dog spot-on products is among the most common avoidable cat emergencies reported to VPIS. UK consensus from International Cat Care is unequivocal: no dog spot-on flea product should be applied to a cat, and treated dogs should be separated from cats until product has fully dried.
Symptoms to watch for
Hidden sources you might not think of
- Dog flea spot-on treatments (many supermarket and pharmacy brands)
- Dog flea collars
- Head lice treatments for humans (some contain permethrin)
- Garden insecticide sprays
Questions owners ask
I put a dog flea treatment on my cat by mistake. What now?
Emergency. Wash your cat with warm water and Fairy Liquid (or similar mild dish soap) to get as much off as possible, then go straight to the vet. Permethrin exposure in cats is frequently fatal without prompt treatment.
My dog was just treated with spot-on — is my cat in danger?
Yes, potentially. Keep them separated for at least 72 hours. Don't let the cat groom the dog or sleep on the dog's bedding.
Related
About this guidance
Every entry on this site is compiled from published UK veterinary toxicology sources — International Cat Care, Veterinary Poisons Information Service (VPIS) references, RCVS-registered practice materials, and peer-reviewed feline medicine literature. Where the evidence is mixed, we err on the cautious side because cats are unusually sensitive to many common substances that are harmless to humans and even to dogs.
This is general information written for UK cat owners. It is not personalised veterinary advice for your specific cat, their age, weight, medical history, or the exact exposure you're dealing with. If your cat has eaten something or is unwell, call your vet first. The Animal PoisonLine on 01202 509000 is available 24/7 for a small fee and can tell you whether an emergency visit is needed.
Entries are reviewed and updated as new research emerges. Spotted an error? Let us know — corrections are investigated and applied within 24 hours. For more context on how we work, see about and our full disclaimer.
Last reviewed: · By the What Can My Cat Eat? editorial team