Fleas are the most common parasite cats get, and the two things owners most often get wrong are assuming indoor cats are safe and treating the cat but not the house.
There is also a genuine safety issue: some dog flea products kill cats. That is worth knowing before anything else.
The warning that matters most
Never use a dog flea product on a cat. Many contain permethrin, which is safe for dogs and toxic to cats, causing tremors, seizures and death.
Cats are also poisoned by contact with recently treated dogs in the same household, so check the product and keep animals separate while it dries.
If a cat is exposed to a permethrin product, treat it as an emergency and contact a vet immediately.
How to check for fleas
You will often not see live fleas, because cats groom them off. Look for the evidence instead.
- Comb through the coat with a fine flea comb, especially at the base of the tail and along the spine.
- Tip the debris onto damp white kitchen paper.
- Look for dark specks that smear reddish-brown — that is digested blood, or flea dirt.
- Check the belly and armpits, where fur is thinner.
- Look for scabbing along the lower back, a classic sign of flea allergy.
The damp paper test is definitive. Ordinary dirt stays dark; flea dirt dissolves into a rusty red smear.
Why indoor cats get fleas
This surprises people constantly, and the routes are mundane.
- Carried in on clothing and shoes.
- Brought in by a dog in the household.
- Present in the home when you moved in — pupae survive months without a host.
- Entering through open windows or from a shared building.
- Arriving with a new cat, particularly one from a shelter or found outdoors.
Flea pupae are the reason infestations recur weeks after treatment. They are resistant to insecticides and can lie dormant, hatching in response to vibration and warmth.
The Companion Animal Parasite Council publishes detailed guidance on flea biology and control.
Treating the cat
| Product type | Effectiveness | Notes |
|---|---|---|
| Veterinary spot-on | High | Most reliable; get the correct species and weight |
| Veterinary oral tablet | High | Fast-acting; useful for immediate knockdown |
| Prescription combination products | High | Also cover worms and mites |
| Supermarket spot-on | Variable | Often less effective; check active ingredient |
| Flea collars | Variable | Some effective, some poor; snag risk |
| Flea shampoo | Low, temporary | Kills on contact only, no residual effect |
| Home remedies | None reliably | Some essential oils are toxic to cats |
Essential oil remedies deserve specific caution. Tea tree, pennyroyal and several others are genuinely toxic to cats, and cats lack the liver enzymes to process many plant compounds safely.
Treating the home — the step people skip
Only a small fraction of a flea population lives on the cat. The rest — eggs, larvae and pupae — is in your carpets, bedding and soft furnishings.
Treating the cat alone produces a cycle of apparent success followed by reinfestation two weeks later.
- Vacuum thoroughly and daily for at least two weeks, including under furniture.
- Empty the vacuum outside immediately after each use.
- Wash all bedding, including yours, at 60°C or higher.
- Treat every animal in the household simultaneously, not just the itchy one.
- Use a veterinary-recommended household spray if the infestation is established.
- Continue treatment for at least three months to break the life cycle.
Vacuuming is genuinely effective and underrated — the vibration also triggers dormant pupae to hatch, exposing them to treatment.
Ticks
Less common on cats than dogs, but they occur, particularly on cats with outdoor access in grassy or wooded areas.
Remove a tick promptly with a proper tick removal tool, gripping close to the skin and twisting steadily upward. Do not burn it, smother it in oil or squeeze the body — all increase disease transmission risk.
Monitor the site for a few days. See a vet if the mouthparts remain embedded, the area becomes inflamed, or the cat becomes lethargic or feverish.
Why fleas are more than an itch
In adult cats a light burden is mostly a nuisance. In kittens it can be fatal.
- Anaemia: heavy burdens cause fatal blood loss in kittens, a common cause of death in outwardly healthy-looking litters.
- Tapeworm: transmitted when a cat swallows an infected flea while grooming.
- Flea allergy dermatitis: severe itching and scabbing from a small number of bites.
- Secondary infection: from persistent scratching and self-trauma.
Any kitten with visible fleas should be treated promptly with a product safe for its age and weight — many adult products are not.
Our guide to what to do when you find newborn kittens covers the wider risks to very young cats, and disease in community cat colonies covers parasites in outdoor populations.
Prevention
Year-round prevention is now generally recommended rather than seasonal treatment, particularly in the Central Valley where mild winters allow fleas to persist.
Ask your vet which product suits your cat’s lifestyle, age and weight. The right prescription product costs little more than a supermarket alternative and works considerably better.
Our guide to how often a cat should see the vet covers where parasite control fits into routine care, and the annual cost of owning a cat covers budgeting for it.
Treating a new arrival
Newly adopted and newly found cats are the most common route for fleas to enter a household, and the first fortnight is when to deal with it.
- Ask the shelter or rescue what treatment was given and when.
- Check the coat with a flea comb before letting the cat mix with resident pets.
- Treat with a vet-recommended product suited to the cat’s age and weight.
- Treat every animal in the household at the same time.
- Keep the new cat in its settling-in room until treated, which limits spread.
The settling-in room serves double duty here — it is already recommended for behavioural reasons and it happens to contain any parasites the cat brought with it.
Our first 30 days with a new cat guide covers the settling-in period, and disease in community cat colonies covers parasites in outdoor cats specifically.
Frequently Asked Questions
Can I use dog flea treatment on my cat?
Never. Many dog products contain permethrin, which is toxic to cats and causes tremors, seizures and death. Cats can also be poisoned by contact with a recently treated dog in the household.
How do I know if my cat has fleas?
Comb the coat with a fine flea comb, especially at the tail base, and tip the debris onto damp white paper. Dark specks that smear rusty red are flea dirt — digested blood — and confirm fleas.
Why does my indoor cat have fleas?
They arrive on clothing and shoes, on a dog in the household, or were already in the home when you moved in. Flea pupae survive for months without a host and hatch in response to vibration.
Why do fleas come back after treatment?
Because only a small fraction of the population lives on the cat. Eggs, larvae and pupae are in carpets and bedding. Treat the home as well, and continue for at least three months.
Are fleas dangerous to kittens?
Yes. Heavy burdens cause fatal anaemia and are a common cause of death in litters that otherwise look healthy. Use only products licensed for the kitten’s age and weight.
How should I remove a tick from a cat?
Use a proper tick removal tool, gripping close to the skin and twisting steadily upward. Never burn it, smother it in oil or squeeze the body, as all increase disease transmission risk.