Ringworm in Cats: Signs, Treatment and Keeping It From Spreading

What it usually means

Ringworm, which vets call dermatophytosis, is caused by fungi that feed on keratin, the protein in skin, hair and nails. The Merck Veterinary Manual reports that about 98 percent of feline cases are caused by one species, Microsporum canis. Spores spread by direct contact with an infected animal and through anything that has touched one: bedding, brushes, carpet, cat trees and carriers. VCA notes that spores can stay infectious in the environment for up to 18 months.

Kittens, longhaired cats, stressed shelter cats and cats with a weakened immune system are most likely to be infected, and their infections tend to last longer or spread wider. Not every patch of hair loss is ringworm, though. Flea allergy, overgrooming, mites and other skin conditions can look very similar, which is why the diagnosis needs tests rather than a guess from a photo.

What ringworm looks like on a cat

The classic sign is a roughly circular patch of hair loss with broken hairs and gray, scaly or crusted skin, most often on the head, ear tips, front legs, paws and tail. Unlike in people, the patch often does not have a red ring, and many cats are only mildly itchy or not itchy at all. Some cats have small crusty bumps across the back instead, and infected claws can look rough, pitted or misshapen.

Mild cases can be almost invisible. VCA describes cats whose only sign is fine scaling in the coat that looks like cigarette ash, and some longhaired cats carry the fungus with no visible signs while still infecting others. If a person in the house develops an itchy, red, ring-shaped rash, that is often the first clue that a pet is the source.

When to call your vet today

Book an appointment promptly if you see patchy hair loss with scale or crust, especially on a kitten, a newly adopted cat, or a cat that has recently been boarded or groomed. Call sooner if the patches are spreading, if more than one pet is affected, or if anyone in the household, particularly a child, an older adult or someone with a weakened immune system, has developed a skin rash.

Also call if your cat is losing weight, has stopped eating, or seems unwell along with the skin changes. Widespread ringworm in an adult cat can be a sign that something else is lowering its defenses, and your vet may want to look for an underlying illness.

When it's an emergency

Ringworm itself is not an emergency. It is uncomfortable and contagious, but it does not threaten a cat's life, and it is reasonable to book the next available regular appointment rather than going to an emergency clinic at night.

A skin problem becomes urgent when it comes with other signs. Go to your vet or an emergency vet the same day if your cat has open, bleeding or oozing wounds, a swelling that is hot and painful, which could be an abscess, a fever or lethargy, or if a kitten is weak, not nursing or not eating.

What you can safely do at home

Until your vet has examined your cat, keep it in one easy-to-clean room, away from other pets and from young children. Wear gloves when you handle it, wash your hands well afterward, and do not share brushes or bedding between animals. Vacuum daily and throw the vacuum bag or contents away outside the house.

Do not use human antifungal creams, tea tree oil or other home remedies. Many are toxic to cats, who lick them off, and partial treatment can make the infection harder to confirm. Once your cat is diagnosed, cleaning becomes part of the treatment: your vet can recommend a household disinfectant or dilute bleach solution that kills spores on hard surfaces, and washing bedding in hot water helps.

What the vet will likely check

Your vet may start with a Wood's lamp, an ultraviolet light under which some ringworm-infected hairs glow yellow-green. It is a quick screen, but many cases do not glow, so a negative result does not rule it out. Hairs plucked from the edge of a patch may also be examined under the microscope. The most accurate test is a fungal culture, which can take up to three weeks to grow, and some clinics also use a faster PCR test.

Treatment usually combines whole-body topical therapy, such as lime sulfur dips or medicated shampoos, with oral antifungal medicine prescribed by your vet. Clipping long hair may be advised. VCA notes that oral treatment generally lasts at least six weeks, and cats are usually rechecked with repeat cultures, because the infection is only considered cleared after two negative results in a row. Stopping early is the most common reason ringworm comes back.

Prevention

Quarantine and check new cats and kittens before they meet the rest of the household, and ask your vet to look at any patchy coat before introductions. Keep grooming tools, carriers and bedding for each cat separate, and clean them regularly. Good nutrition, flea control and low stress all help a cat's skin defend itself.

If you have had a case at home, finish the full course of treatment and keep cleaning until your vet confirms the cat is clear. Anyone in the family with a ring-shaped rash should see their own doctor, since ringworm is one of the most common infections shared between pets and people.

This page is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your pet.