Fleas on Cats: How to Spot, Treat and Keep Them Away

"But she never goes outside."

It's the first thing I hear when an indoor cat turns out to have fleas, and it's a fair objection. The tricky part is fleas come in on your clothes, on the dog, and with the rodents in your roof.

What makes cats harder is that they groom away the evidence. A cat can have a genuine infestation, and you'll never see an insect, just a thinning patch on her belly or small scabs along her back. By the time it looks obvious, the house usually has fleas too.

I'll take you through what to look for when there's nothing to see, how to clear the cat and the house together, and which products are safe to use.

Look for what the fleas have caused, because a grooming cat removes most of the evidence.

This is the central difficulty with cats. A cat that grooms well swallows the adult fleas and the flea dirt along with them, so you can have a genuine infestation and never see an insect.

• Over-grooming, often to a symmetrical thin patch on the belly, the back legs or in front of the tail. 
• Small crusty scabs along the back and neck, a pattern vets call miliary dermatitis. 
• Sudden bursts of grooming, skin that twitches, or a cat who seems restless without explanation.

The flea comb test still works and is worth doing. Comb the base of the tail, the back of the neck and the belly, then tap the debris onto damp white paper. Ordinary dirt stays dark. Flea dirt spreads into a rust-red bloom, because it is digested blood.

Treat every pet in the house with a product registered for its species on the same day, then treat the home itself. Expect three to six weeks before you stop seeing fleas, and up to three months before the household is genuinely clear.

Start with a product registered for cats

Use a veterinary flea product suited to your cat's weight and age, which is what our cat flea treatments range is sorted by. Spot-ons and oral products kill fleas within hours and keep working for weeks to months, depending on the product.

Spot-ons do most of the work in cats.

• Bravecto and Felpreva stretch further between doses.
• Revolution Plus and Advocate are monthly and add intestinal worm and heartworm cover, though neither treats tapeworm.
• Advantage is flea-only if that is all you need.

If your cat already has fleas today and you want them off her within the hour, Capstar is an oral knockdown dose, though it does nothing beyond that day and needs a longer-acting product behind it.

Applying a spot-on correctly

Part the fur at the back of the neck, high enough that your cat cannot turn and lick it. Apply the liquid onto the skin rather than onto the coat. Empty the whole tube. Keep other pets from grooming the site until it dries, and do not bath your cat for at least 48 hours. A spot-on applied to fur instead of skin is a common reason a treatment appears not to work.

Treat every pet at once, dogs included

An untreated animal in the house is a breeding site. The fleas on it lay eggs into your carpet every day, and those eggs become the next wave that lands on everyone, so treating the cat alone in a two-pet house only slows the cycle down. Use a product registered for each species, so the dog goes onto something from our dog flea treatments range rather than a share of the cat's dose.

Treat your home

Most of the fleas are here rather than on your cat, and this is the step people skip.

• Vacuum daily for the first fortnight, including under beds and furniture, along skirting boards, and anywhere your cat sleeps. Empty the vacuum into an outside bin each time.
• Wash all bedding at 60°C. A hot dryer cycle helps as much as the wash.
• Do not forget the less obvious places: the top of the wardrobe, the back of the couch, the cat tower, and any sunny windowsill she favours.
• Keep it up for several weeks. One thorough clean will not do it.

Vacuuming does more than lift eggs and larvae. The vibration and warmth prompt pupae to hatch, which brings them out of their protective casing and into contact with the product on your cat. Studies of treated animals in simulated home environments show this is how a product on the animal eventually clears the flea stages living in the house.

A flea goes from egg to adult in as little as two to three weeks, and only about 5% of a flea population is on your cat at any moment.

That 5% figure is the single most useful thing to understand about fleas. The adults you can see, or in a cat's case usually cannot, are the small visible part of a much larger population living in your house.

Here is what the other 95% is doing.

Eggs. An adult female starts laying within a day or two of her first meal and produces around 50 eggs a day. They are smooth and not sticky, so they roll off your cat wherever she sleeps and walks.

Larvae. The eggs hatch into small larvae that avoid light and burrow into carpet fibres, cracks in floorboards, soil and bedding. They feed on flea dirt dropped by the adults above them.

Pupae. The larvae spin a sticky cocoon. This is the problem stage. The cocoon resists insecticides and almost everything else, and the flea inside can wait months for a signal that a host has arrived: vibration, warmth, carbon dioxide.

Adults. They emerge, find a host within hours, and start the cycle again.

In a warm humid house the loop can run in two to three weeks. In a cool one it stretches out considerably, and the pupae simply wait. That is why clearing a household takes weeks to months rather than days, even when you do everything correctly.

A cat that swallows a flea while grooming will pick up tapeworm, so flea control and worming work as a pair rather than as separate jobs.

The mechanism matters because it explains a frustration. Flea larvae in the carpet eat flea dirt, and in doing so they can swallow tapeworm eggs. Your cat grooms, swallows an infected flea, and the tapeworm matures in her gut.

What you notice is small pale segments like grains of rice, moving near the tail or dried onto bedding.

The consequence is that worming a cat while the fleas are still there usually means the tapeworm comes back. The wormer clears what is present, and she re-infects herself the next time she grooms. So run the two together: a flea product plus something from our cat worming treatments range that covers tapeworm, or a single all-in-one treatment that does both. Our guide to worms in cats covers what each product class treats.

New fleas keep appearing for weeks after correct treatment, because the pupae in your carpet were never reachable by the product on your cat.

If you have treated properly and are still finding flea dirt at week three, that is the expected pattern rather than a failure. Each newly hatched flea jumps on, feeds, and dies from the product your cat is carrying. You are watching the reservoir empty.

Treatments do genuinely fail sometimes, usually for one of these reasons.

• A pet in the house was missed, or is on a different schedule.
• A spot-on went onto fur rather than skin, or the cat licked it off before it dried.
• The dose was wrong for her weight.
• The product was out of date, or stored somewhere hot.
• The house was never treated, so the reservoir is still full.

If none of those apply and you are still finding live fleas after two months of consistent treatment, speak to your vet rather than switching brands.

See a vet if your cat is still itching after the fleas are gone, or if a kitten is pale, weak or lethargic.

Most flea problems are handled at home, but three situations are worth a call.

Flea allergy dermatitis. Some cats are allergic to flea saliva, and for those cats a single bite triggers days of itching. This is why the itchiest cats often have the fewest visible fleas, and why their owners are frequently certain fleas are not the cause. Treatment usually needs prescription relief for the itch alongside strict flea control. 

Our guide to skin conditions in cats covers how flea allergy dermatitis is diagnosed and what else produces the same itch.

Skin infection. Persistent grooming and scratching break the skin. Weeping patches, crusting, a smell, or bald areas that keep spreading need veterinary treatment rather than another flea product.

Anaemia. Heavy flea burdens take enough blood to matter in kittens, and in small or elderly cats. Pale gums, weakness, fast breathing or collapse need same-day attention.

Some dog flea and tick products contain permethrin, which is safe for dogs and can kill a cat.

This is the most important safety point on this page. Cats break down compounds like permethrin far more slowly than dogs do, so a dose a dog clears without trouble can build up in a cat.

Your cat does not have to be treated with it to be harmed. Most cases follow a dog product being applied to a cat by mistake, but grooming or sleeping against a recently treated dog can be enough. Signs include drooling, muscle twitching, tremors, unsteadiness and seizures, and they are a same-day emergency.

If you have both species at home, either choose a dog product without permethrin or keep the animals apart for 48 hours after the dog is treated, which is the manufacturer's own advice rather than simply waiting for it to dry. Our guide to fleas on dogs covers which dog products carry it.

Never split a dog dose for a cat, and never use a product simply because it says it is for pets. Check the pack names cats specifically.

Kittens need a product registered for their age and weight, and a heavy flea burden in a kitten is urgent rather than routine.

Flea products carry minimum age and weight limits, and those limits vary between products, so check the pack rather than assuming a smaller amount of an adult product is safe. Our kitten flea, tick and worm treatments range is filtered to products registered for the smallest weight bands, which saves working through the adult range.

For a kitten too young for any registered product, the approach is physical. Comb fleas out with a fine flea comb over a bowl of soapy water, and treat the mother if she is still nursing. Treat the environment thoroughly too, because that is where the pressure is coming from.

Watch for anaemia. A kitten carries very little blood, and a heavy burden can take a dangerous amount of it. Pale gums, lethargy or weakness in a kitten with fleas is a same-day vet visit.

Flea prevention runs all year for most Australian cats, and a heated house keeps the cycle going through a southern winter.

Season and climate by region

In Queensland and northern New South Wales, conditions suit fleas more or less permanently and there is no off season. Further south, numbers climb from spring and peak through summer and early autumn.

The catch in cooler states is indoors. Heating holds a house at exactly the temperature flea eggs and larvae prefer. A winter break in prevention often produces a surprise infestation in a home that felt far too cold for one. Our guide to year-round parasite prevention across Australia maps this by region.

Choosing a product for your cat

Spot-on treatments are the mainstay for cats, applied to the skin at the back of the neck and lasting a month or more depending on the product. Oral products suit cats that will take a tablet, which is a smaller group than it is with dogs. Collars run for months and suit cats that are difficult to handle, provided the collar is a safety-release type, which is what the Seresto cat collar uses.

Many cat products combine flea cover with worming and sometimes ticks, which suits a cat going outdoors in a tick area. If you would rather run one product than three, our cat flea, tick and worming treatments range is where the combination products sit. Our guide to paralysis ticks on cats covers what to look for on the label.

Treat the whole household, permanently

Prevention on one animal in a multi-pet house leaves a gap. The most reliable arrangement is every animal on a product, on the same schedule, year-round, with a diary reminder rather than a mental note.

If the choice is what is holding you up rather than the method, our guide to the best flea, tick and worm treatments for cats sets the main options side by side on weight range, what each one covers, and how often it is due.

Two of them come up often enough to be worth a direct comparison: Advocate vs NexGard Spectra for cats works through where each one fits. Both are monthly spot-ons covering fleas, heartworm and intestinal worms, and the difference that matters is that Advocate does not cover paralysis ticks or tapeworm.

If you are in the middle of an infestation, the timeline is the thing worth holding onto. Consistent treatment of every pet plus the house clears almost every case, and finding flea dirt in week three does not mean it has failed.

After that, prevention is a far smaller job than the clean-up ever was. 

Our guide to the best cat flea, tick and worm treatments covers how fleas fit alongside ticks and worms in one plan.