Flea collar stopped working? Best cat flea treatment

It sounds like your Ragdoll's flea collar did the job for a while and then just... stopped keeping up — that's a frustrating but actually quite common pattern with collars. Before I suggest an alternative, I want to flag something important for any cat owner: permethrin and certain other insecticides that are perfectly safe for dogs are toxic to cats, and using the wrong product can be fatal, so it matters that we pick something cat-specific. A couple of quick questions: how heavy is your Ragdoll, is this an active infestation right now or are you looking to get back on a prevention routine, and have you treated your home and soft furnishings yet?

Good to know — at 5.5 kg she's well within the adult cat range, so that's straightforward. The house is actually a crucial piece of this: up to 95% of a flea population lives in the environment as eggs, larvae, and pupae rather than on the cat, which is almost certainly why the collar kept failing. Fleas were re-infesting her from the carpets and upholstery faster than the collar could kill them. Before I give you my recommendation for her, can I ask — do you have any dogs in the house, or is she your only pet?

Perfect — that actually makes things simpler, since you don't have to juggle a cat-safe and dog-safe product at the same time. For your Ragdoll I'd recommend Advantage spot-on for cats over 4 kg. It's imidacloprid-based, which is well-tolerated by cats, kills adult fleas on contact within 24 hours without needing a bite to activate, and is water-resistant enough to stay effective through normal grooming. It's available in single or multi-pipette packs on Amazon UK and is widely stocked by vets too. For the house, use a household flea spray that contains an insect growth regulator — something like Indorex Defence — at the same time as you apply the spot-on, and vacuum thoroughly first. If you don't tackle the environment alongside treating her, you'll be back in the same cycle in a few weeks.

Advantage is applied once a month, and you apply it to the skin at the back of the neck — the spot she can't easily reach — precisely to minimise ingestion during grooming. The amount she might lick from her coat during normal grooming is not considered harmful, but the neck placement keeps it well away from her mouth. Let it dry fully before you let her interact with children or other animals, which usually takes around 30 minutes. The main thing to avoid is bathing or getting her very wet within 48 hours of application, since that can reduce absorption.

One application of Advantage on your cat will kill the adult fleas on her quickly, and one thorough treatment of the home with Indorex will deal with the environmental stages and keep working for up to 12 months because of the growth regulator. That said, you'll likely see a few new adult fleas emerging over the following 2–3 weeks as pupae hatch — flea pupae are resistant to sprays and will only emerge when they detect vibration and warmth. Don't panic when that happens; it doesn't mean the treatment failed. Keep vacuuming regularly to encourage them to hatch, and the monthly Advantage on your cat will catch them. By the second month you should be clear. The key is not going back to a collar — they're the weakest option for an active infestation.