Protecting your cat when your dog has fleas

Your situation is actually a race against time — your dog already has fleas, which means your Selkirk Rex is being exposed to them right now, even if you haven't spotted any on her yet. Before we get into options, one critical safety point: never use a dog flea product on a cat. Permethrin and several related insecticides found in many dog treatments are toxic to cats and can be fatal — so whatever you use on your dog, keep your cat well away until it's fully dry, and never apply it to her directly. Now, to point you toward the right product for your cat: how heavy is she, and is she an indoor cat, outdoor, or both? And can you tell me what product your dog is currently on for his fleas?

Good to know — Frontline Spot On for dogs contains fipronil, which is fine, no permethrin risk there for your cat. That said, Frontline's flea-killing speed has become a concern in recent years because flea resistance to fipronil is now widespread in the UK. Since your dog already has fleas and your cat is being exposed, I wouldn't want to put her on a product with the same active ingredient that's already struggling on the dog. You want something fast-acting and from a different chemical class. Has your cat had any flea treatments before, or is this the first time you're looking?

Completely understand, and you're right to be careful — especially with a first treatment. For your cat right now, I'd recommend Advantage 80 for cats (the spot-on by Bayer, now marketed under Elanco). It contains imidacloprid, which is a completely different class of insecticide from the fipronil your dog is on, and it kills fleas on contact — fleas don't even need to bite to die, which matters because it starts protecting your cat before an infestation can establish. It's safe for cats from 4kg and above, so at 4.5kg your Selkirk Rex is well within range. It's a once-monthly spot-on, easy to apply, and widely available on Amazon UK. One important note: because flea eggs are almost certainly already in your home environment, you'll also want to treat the house with a household flea spray — something like Indorex or RIP Fleas — otherwise the cycle will keep going regardless of what you put on the animals. Have you done any home treatment yet?

Fairly urgent, honestly. Up to 95% of a flea infestation lives off the animal — in carpets, sofas, and bedding as eggs, larvae, and pupae. If your dog has had fleas for more than a few days, those stages are already in your home. Treat the animals first, then spray the home within the next day or two if you can. Indorex Defence Household Flea Spray is a solid choice — it kills adults on contact and contains an insect growth regulator that stops eggs and larvae developing for up to 12 months. One can covers a standard house. Vacuum thoroughly before you spray, then leave it to work. Between Advantage 80 on your cat, sorting your dog's treatment, and one good home spray, you should be able to break the cycle without it ever properly taking hold on your Selkirk Rex.

No, Advantage 80 doesn't contain permethrin, so there's no danger to your cat from the dog, and no danger to the dog from your cat. Just let the application site dry before they curl up together — usually a couple of hours — and you're fine. The main permethrin risk runs the other way: dog-to-cat, if a dog product containing permethrin gets onto a cat through grooming or close contact. Since your dog is on fipronil-based Frontline, that's not an issue here either. You're in a straightforward situation — just move quickly on the home treatment and you should keep your cat flea-free.