Ringworm in Cats: Not a Worm, But Still a Serious Problem
Despite the name, ringworm has nothing to do with worms. It is a fungal infection caused by dermatophyte fungi — most commonly Microsporum canis in cats — that colonise keratinised tissues including skin, hair, and claws. The name comes from the circular lesions the infection sometimes produces in humans.
Ringworm is one of the few pet diseases that transfers readily between cats and humans, making it a condition that demands prompt attention and a systematic approach to treatment that encompasses the whole household, not just the affected animal.
How Cats Get Ringworm
Dermatophyte spores are remarkably resilient. They can survive in the environment for 12 to 24 months under suitable conditions and are resistant to many common disinfectants. Transmission occurs through direct contact with an infected animal, contact with contaminated objects — bedding, grooming tools, furniture — or exposure to a contaminated environment.
Kittens under one year are by far the most susceptible group, partly because of their developing immune systems and partly because of social grooming behaviours that facilitate direct transmission. Long-haired breeds including Persians and Maine Coons are also disproportionately affected, likely because their coats provide more surface area for fungal colonisation and make thorough inspection more difficult.
Cats can carry dermatophytes without showing clinical signs — asymptomatic carriers can spread infection widely through a household or cattery without appearing unwell themselves. This is a significant challenge in multi-cat environments.
Recognising Ringworm in Your Cat
The classic presentation is one or more areas of hair loss, typically circular, with a scaly or crusty appearance at the margins. The lesions often appear first on the head, ears, and forelimbs. The skin within and around the lesion may look reddened, and the broken hair shafts in the affected area give the coat a moth-eaten appearance.
However, ringworm does not always look like the textbook picture. Some infected cats show only mild scaling or dandruff-like changes. Others may have more generalised or diffuse hair loss. A subset show no skin changes at all but are actively shedding spores. Miliary dermatitis — tiny crusted papules distributed across the body — can also be a presentation in some cats.
A Wood's lamp (ultraviolet light) examination can be a useful screening tool because Microsporum canis fluoresces apple-green under UV light. However, only around 50 per cent of strains fluoresce, and other materials including topical products can produce false positives, so Wood's lamp findings are never used in isolation.
Definitive diagnosis requires fungal culture — hairs and scale from the lesion margin are plated on a dermatophyte test medium and incubated for up to three weeks. PCR testing can provide faster results and is increasingly available. Your vet may also take skin scrapings for microscopic examination.
Treating the Infected Cat
Treatment of an individual cat with ringworm is usually multimodal, combining systemic antifungal medication with topical therapy.
Systemic Antifungals
Itraconazole is the most widely used systemic antifungal for feline ringworm and has a strong evidence base supporting its efficacy. It is typically given daily or in pulse-dosing protocols — one week on, one week off — for a minimum of six to eight weeks. Terbinafine is an alternative, particularly in kittens where itraconazole may be less well tolerated. Treatment continues until two consecutive negative cultures are obtained, not simply until lesions appear to have resolved.
Topical Therapy
Topical treatment serves two purposes: killing fungal elements on the skin and coat surface and reducing environmental spore contamination. Twice-weekly whole-body treatment with lime sulphur dip or enilconazole rinse is recommended. These products are unpleasant in smell and application but are the most effective topical agents available. Miconazole-chlorhexidine shampoo is an alternative that owners may find more practical to apply consistently.
Clipping long-haired cats reduces fungal load on the coat and makes topical treatment more effective, though the clipped hair must be carefully disposed of as infected material.
Treating the Environment: Non-Negotiable
Environmental decontamination is not optional — it is central to successful resolution. Without it, reinfection from contaminated surfaces perpetuates the cycle regardless of how well the cat responds to medication.
- Vacuum all carpets, upholstered furniture, and curtains daily during active infection, disposing of the vacuum bag immediately after each use
- Wash all bedding, soft toys, and fabric items at 60 degrees Celsius or higher twice weekly
- Disinfect hard surfaces daily with a dilute bleach solution (1 part household bleach to 10 parts water) or an accelerated hydrogen peroxide product known to be effective against dermatophytes
- Discard or thoroughly disinfect all grooming tools, collars, and harnesses
- Restrict the infected cat's access to as few rooms as possible during treatment to limit environmental spread
Protecting Human Members of the Household
Because ringworm is a zoonotic disease — transmissible from animals to humans — everyone in the household needs to be aware of the risk. Lesions in humans typically appear as red, itchy, circular patches on exposed skin. Children, elderly individuals, and immunocompromised people are at greatest risk of contracting the infection and developing more significant disease.
Basic precautions during the treatment period include washing hands thoroughly after handling the infected cat, avoiding sleeping in the same bed as the cat, and monitoring skin closely for any new lesions. Human ringworm responds well to topical antifungal creams available over the counter, but a GP appointment is warranted if lesions are spreading or fail to resolve promptly.
When Will It Be Over
Ringworm treatment is a marathon, not a sprint. The minimum realistic timeline for resolution in a single-cat household is six to eight weeks of rigorous treatment. In households with multiple cats, some of whom may be asymptomatic carriers, or where environmental contamination is heavy, treatment can extend to three or four months.
Persistence with both the animal treatment and the environmental decontamination programme is what determines success. Owners who maintain consistent treatment and environmental management throughout the full course virtually always achieve complete resolution.