Repellents & petsProtecting dogs and cats from bugs

A monthly liquid applied between the shoulder blades. The permethrin dog versions genuinely repel mosquitoes and flies; the cat version manages fleas and ticks but is not a mosquito repellent.

The evidence: Strong. Permethrin is one of the best-studied insecticides there is, and controlled studies show permethrin spot-ons both repel and kill mosquitoes, sandflies, ticks, and biting flies on dogs. Among widely available options this is one of the best-supported wearable repellents for a dog. Two honest caveats: repellency is high but not total and wanes toward the end of the month, and permethrin can be lethal to cats.

A flavored tablet the pet eats. These kill fleas and ticks after they bite rather than repelling them, so they are excellent against tick-borne disease and (for the heartworm-covering ones) the real mosquito threat, even though they do not stop the bite itself. Prescription, usually through your vet or Chewy.

The evidence: Strong for what they do. FDA approval required controlled trials, and the isoxazoline chews reliably kill fleas and ticks. The honest limit is the mechanism: the insect has to bite and feed to pick up the dose, so a chew does not prevent the bite, it kills what bites. Against ticks the kill is usually fast enough to cut the risk of disease, though it reduces rather than eliminates it, and it does nothing for mosquito nuisance.

A collar that slowly releases its active for months of flea and tick control. Common, but not something we recommend.

We do not recommend flea and tick collars. The dominant one, Seresto, is under an unresolved federal safety controversy: tens of thousands of adverse-event reports, including pet deaths, led to an EPA review, and in 2024 a federal watchdog said the agency still had not established that it is safe. It remains legally sold and some vets stand by it, but with effective, better-understood spot-ons and oral chews available, we do not think the trade is worth it. Counterfeits are also rampant. If you already use one, watch your pet closely and take it off at the first sign of a reaction.

Protect the pet without putting anything on it. This is the safest route of all for cats.

The evidence: Solid, within limits. A net or screen is a chemical-free barrier that works when the mesh is fine enough for the insect and there are no gaps, though it protects an enclosure rather than a pet roaming outside it. Metofluthrin area repellers like Thermacell have peer-reviewed data showing real drops in mosquito landing across a treated zone, best in low wind and close range. Neither touches the animal, which is why they are the safe backbone, especially for cats.