Ringworm in cats: how to recognise it, how it is treated and how to clean your home
Ringworm is not a worm but a fungus, and in cats it is one of the most common skin infections, especially in kittens and Persians. It can be cured, but treatment is long and has three legs: the cat, its companions and the home. And since it spreads to people, it pays to do it properly from the start.
What ringworm is
Ringworm, or dermatophytosis, is an infection of the surface layer of the skin, the hair and sometimes the claws caused by dermatophyte fungi. In cats, the culprit in the vast majority of cases is Microsporum canis. The fungus produces spores that stay on the hairs the cat sheds and can survive in the environment for many months. It spreads by direct contact with an infected animal or with its hair, blankets, brushes and carriers. It is more common in kittens, in cats from rescues, colonies or breeders, in long-haired cats such as Persians and in cats with weakened immunity. Many healthy adult cats clear it on their own in time, but treatment greatly shortens the process and reduces spread.
What it looks like
The classic picture is round hairless patches with greyish scaling and sometimes scabs, especially on the head, face, ears and front legs. It often does not itch, or itches only a little, which sets it apart from allergies. But in cats ringworm is a great imitator: it can cause widespread scaling without bald patches, brittle hair, scabs resembling miliary dermatitis, small bumps, deformed claws or even nodules under the skin in Persians. And some cats are carriers with no visible lesions that pass it on to other animals or people. So if someone in your home has a round red patch on their skin and there is a newly arrived cat, it is worth having the cat examined.
Spread to people
Feline ringworm is a zoonosis: it passes to people, especially children, older people, those with weakened immunity and anyone who cuddles the cat a lot. In humans it usually causes a round red patch with a more defined edge and scaling, often on the arms, neck or face. It is not serious in healthy people, but it does need treating: if someone in the family has a lesion like that, they should see their doctor and say they live with a cat that has ringworm. There is no need to give up the cat or isolate it completely, but hygiene should be stepped up during treatment: wash your hands after touching it, limit young children’s contact and do not let it sleep on the bed.
How it is diagnosed
The vet can use several tests, and usually combines them. The Wood’s lamp is an ultraviolet light under which some hairs infected with Microsporum canis glow apple green, but not every case fluoresces, so a negative lamp test does not rule out ringworm. A trichogram, examining hairs under the microscope, can show the spores. A fungal culture, in which the whole cat is brushed with a sterile toothbrush and the sample placed on a special medium, is the reference test and takes a few days to give a result. PCR is faster and very sensitive, although it can come back positive from traces of dead fungus. These tests are also used to confirm the cat is cured.
Treatment: oral, topical and the environment
International veterinary dermatology guidelines recommend treating with two tools at once. A veterinary oral antifungal, which works from the inside and which the vet prescribes according to the cat’s weight and age, with monitoring if needed. And a topical treatment of the whole body, not just the lesions, usually baths or rinses twice a week with veterinary antifungal products, which kill the spores in the coat and reduce spread. In long-haired cats, clipping the coat is sometimes recommended so the treatment reaches the skin better, taking care not to irritate it. Creams on a single bald patch are not enough: the fungus is usually in more places than you can see.
How long it lasts and when it is cured
You need patience. Treatment usually lasts several weeks, often six to twelve, and sometimes longer in long-haired cats, large groups of cats or animals with other illnesses. The lesions improve before the cat is cured, so treatment is not stopped when the hair grows back. A cat is considered cured when the follow-up cultures or tests come back negative, and many vets want two negative results in a row before signing it off. Stopping too early is the most common cause of relapse.
How to clean your home
The spores that fall with shed hair are the source of reinfection, and cleaning is as important as treating the cat. The most effective approach is mechanical cleaning: vacuum floors, sofas and rugs daily or every few days, dispose of the bag or empty the container outside, and wash hard surfaces with detergent. Then disinfect with diluted bleach on surfaces that tolerate it, or with disinfectants proven to work against fungal spores, always rinsing and with the cat out of the room. Wash blankets, covers and bedding in the washing machine on a hot cycle. While treatment lasts, it helps a lot if the cat lives in an area of the home that is easy to clean. Cardboard scratchers and beds that cannot be washed are best replaced at the end.
What it costs in Spain in 2026
As a guide: consultation, €40 to €70; Wood’s lamp and trichogram, €15 to €40; fungal culture or PCR, €30 to €80 each, and at least two or three will be needed over the course of treatment. The oral antifungal, €20 to €60 a month depending on weight and product. Topical antifungal products, €15 to €40 per bottle. If monitoring blood tests are needed during treatment, €60 to €120 each. In total, a simple case in one cat usually comes to between €200 and €450 from start to finish, and considerably more if there are several cats or treatment drags on.
What not to do
Do not use human antifungal creams on the cat: they do not treat the whole body and the cat licks them off. Do not use essential oils or remedies with vinegar or garlic, which do not work and can be toxic. Do not stop treatment when the hair grows back without a negative test. Do not forget the other animals in the house, even if they have no lesions: the vet will decide whether they need testing or treating. Do not take the cat to a cattery or put it with other cats until it is cured. And do not forget the cleaning: treating the cat in a home full of spores means starting again and again.
Prevention
If you adopt a cat, especially a kitten or a long-haired cat of unknown origin, take it to the vet before introducing it to other animals and mention any bald patches or scaling. Keep newcomers apart for a few days. Brush your cat regularly and check its skin. Wash beds and blankets often. In breeding establishments and homes with many cats, any suspicious lesion should be investigated quickly, because a ringworm outbreak in a large group is much harder to eradicate. And good nutrition, parasite control and general health help the immune system keep the infection in check.
Ringworm is a fungus that causes round bald patches and scaling, spreads to people and is cured with patience: an oral antifungal, topical treatment of the whole body and thorough cleaning of the home, until the tests come back negative. Do not stop when the hair grows back.
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.