Fleas and ticks in cats: how to get rid of them and the mistake that can kill
An indoor cat can get fleas too. And if they have them, what you see on the cat is a small part of the problem: most are in your home, as eggs and larvae. But first, the most important point in this article: flea treatments for dogs can kill a cat.
First, the warning: permethrin
Many spot-ons, sprays and collars for dogs contain permethrin or other pyrethroids, which are safe in dogs but highly toxic to cats, because their liver cannot break them down properly. One dog spot-on applied to a cat, or a cat sleeping pressed against a freshly treated dog or licking it, is enough to cause tremors, muscle twitching, drooling, fever and seizures that can be fatal. If it has happened, go to the vet immediately and take the packaging; washing the cat with lukewarm water and mild washing-up liquid before you leave may help if you are told to. Always use products specifically labelled for cats, and if you live with a dog, ask which product is safe for the household.
How to tell if they have fleas
Cats groom so much that they often swallow the fleas and you never see them. The signs are scratching, especially on the neck, head and around the tail, excessive licking, small scabs like tiny spots along the back and neck (miliary dermatitis) and patches of thin fur on the belly or thighs. The most reliable test: run a very fine-toothed flea comb along the back and the base of the tail over a damp sheet of white paper. If tiny black specks fall out and leave a reddish smear when wet, they are flea droppings containing digested blood. Even if you do not see a single live flea, that confirms they are there.
Why an indoor cat gets fleas
Fleas come into the home on clothes and shoes, with a dog, with another cat, from the landing or a garden, or they were already in a new home as pupae that can wait months for an animal to pass by. On top of that, a centrally heated home lets them breed all year round. That is why vets recommend protecting cats that do not go out as well, adjusting how often to the risk. A cat that lives with a dog that goes to the countryside or the park, or a cat that goes out into the garden, is at clearly higher risk.
Why treating the cat is not enough
Only a small percentage of the flea population is on the cat as adults; the rest, the vast majority, are eggs, larvae and pupae spread across floors, rugs, the sofa, the cat's bed and cracks. The adult flea lays dozens of eggs a day, which drop onto the floor. So even if the product kills the fleas on the cat, new ones will keep appearing for weeks as the pupae hatch. Effective treatment combines three things: a flea product for cats, kept up for at least three months; treating all the dogs and cats in the home at the same time; and cleaning the environment.
Which products work
There are spot-ons, tablets and collars made specifically for cats with different active ingredients and different durations, and some also protect against ticks, ear mites or worms. Your vet will help you choose according to the cat's age and weight, whether they go out, whether there are dogs at home and whether they have flea allergy. Always use the product for your cat's weight and never split or share spot-ons between animals. Natural remedies such as vinegar, garlic, which is toxic to cats, or essential oils, which can be too, do not work and can do harm. And cheap supermarket collars with no evidence behind them are usually not very effective.
Cleaning the home without losing your mind
Vacuum floors, rugs, sofas, mattresses, skirting boards and the inside of the car thoroughly for several weeks, and empty the bag or canister outside the home after each use. The vibration of the vacuum cleaner also makes the pupae hatch, and they then die from the treatment. Wash the cat's bedding, blankets and cushions at 60 °C (140 °F). Household sprays with insect growth regulators help with large infestations; if you use one, follow the instructions and keep the cat out of the room until it has dried. Be patient: it is normal to keep seeing the odd flea for one or two months even when everything is going well.
What fleas can transmit
Besides itching, fleas can cause flea allergy dermatitis, an intense reaction in which a single flea is enough to make the cat scratch non-stop; anaemia in kittens with heavy infestations; the tapeworm Dipylidium caninum, which the cat swallows while grooming and which looks like grains of rice in the faeces or around the bottom; and bacteria such as Bartonella henselae, responsible for cat scratch disease in people, or Mycoplasma haemofelis, which destroys red blood cells. That is why, when treating fleas, the vet usually also recommends a wormer that covers tapeworm.
Ticks: less common, but they exist
Cats that go into the countryside, overgrown gardens or rural areas can pick up ticks, especially on the head, neck, ears and between the toes. If you find one, remove it with a tick hook or fine tweezers, gripping it as close to the skin as possible and twisting or pulling gently and steadily, without squashing it. Do not put oil, alcohol, hairspray or heat on it first: they make the tick regurgitate and increase the risk of passing on disease. Disinfect the area and watch the cat over the following days. If they are flat, feverish or have pale gums in the weeks afterwards, see the vet.
What it costs and how often
As a guide in Spain in 2026, an external parasite treatment for cats costs between 8 and 20 € per month of protection depending on the product and format; a good-quality long-acting collar, 25 to 45 € for several months. Protecting a cat all year round comes to around 60 to 180 €. Treating an infestation with cleaning of the home and treatment of all the animals can cost quite a lot more, especially in homes with several animals. A consultation for flea allergy dermatitis, 40 to 70 €, plus medication for the itching if needed. Prevention is clearly the cheapest option.
Never use dog spot-ons or collars on a cat: permethrin can kill them. If they have fleas, treat every animal in the home with suitable products for at least three months and clean the environment, because most fleas are not on the cat but in your home.
Educational content from Michipedia, translated from the Spanish original. It does not replace the advice of a vet or a feline behaviour specialist. Every cat is an individual.