Ringworm (dermatophytosis) in cats

Symptoms an owner can spot at home

• Circular patches of hair loss, classically on the face, ear tips, and forelimbs
• Scaling, crusting, or broken stubbly hairs at the edge of a lesion
• Mild or absent itch in many cats, which is why it goes unnoticed
• Inflamed, thickened nail folds or brittle claws in some cases
• Asymptomatic carriage: long-haired cats can shed spores with no visible lesion at all

When to see a vet

• Any circular area of hair loss, especially in a kitten or a newly adopted cat
• Lesions spreading, or a second pet developing patches
• Itchy red rings appearing on people in the household, particularly children or anyone immunocompromised
• Lesions that worsen after over-the-counter antifungal cream, self-treating obscures the diagnostic tests
• Nail or claw-bed changes, which need a longer and different course

What it is

Dermatophytes are keratin-digesting fungi that colonise the hair shaft and outer skin. In cats, Microsporum canis dominates. Infection spreads by direct contact with an infected animal and, just as often, by contact with infected hairs shed into the environment; arthrospores on those hairs remain viable for many months. Kittens, long-haired cats, shelter and cattery populations, and immunosuppressed cats are the highest-risk groups.

It is zoonotic. Human infection presents as an itchy expanding ring with a raised border and is generally straightforward to treat, but it means household hygiene is part of the veterinary plan rather than an afterthought. It is also, importantly, a curable disease. In an otherwise healthy cat, dermatophytosis is self-limiting over months even untreated; treatment exists to shorten the course and, critically, to cut environmental contamination and transmission.

How vets diagnose it

No single test stands alone. A Wood's lamp examination is a useful screening step but only a subset of M. canis strains fluoresce, and the apple-green glow must follow the hair shaft, scale and topical residues fluoresce differently and cause false positives. Direct microscopy of plucked hairs can show fungal invasion immediately.

• Fungal culture on dermatophyte test medium remains a reference method and also confirms cure, though it takes days to weeks.
• PCR gives a fast answer but detects fungal DNA from dead organisms too, so it can stay positive after successful treatment and is not a standalone cure test.
• Cure is defined by clinical resolution plus consecutive negative cultures, not by 'the patch looks better'.

Treatment overview

This is editorial overview, not a treatment plan; your vet builds the plan. Current consensus guidance treats dermatophytosis on three fronts at once: systemic antifungal therapy, topical whole-body therapy applied twice weekly to kill spores on the coat, and environmental decontamination. Topical therapy is not optional garnish; it is the component that stops the cat re-seeding its own environment and infecting housemates.

Guidelines note that routine full-body clipping is generally not recommended for shorthaired cats, since microtrauma to the skin can worsen lesions; clipping decisions belong with your vet. Courses typically run several weeks and are stopped on test results, not on appearance. Stopping early is the most common cause of an apparent relapse.

What owners can do

• Confine the infected cat to one easily cleaned room, hard floors, minimal soft furnishing, for the duration of treatment.
• Choose washable, machine-dryable bedding and launder it frequently. Mechanical removal of infected hairs is the core of decontamination; a hot wash plus a full dry cycle is effective.
• Vacuum daily and dispose of the contents. Removing hair is the highest-yield environmental step, ahead of any spray.
• Use non-porous, disinfectable grooming tools and stop sharing brushes between cats. Wipe down hard surfaces with an appropriate disinfectant after mechanical cleaning; disinfectant applied over hair and dust does nothing.
• Wear gloves for handling and topical treatment, and wash hands afterwards. See a doctor for any human lesion rather than treating a family member from the pet's medication.
• Keep every in-contact animal in the assessment plan, even the ones that look clear; asymptomatic carriers are how households stay infected.
• Reduce stress, resident cats in a treatment routine benefit from vertical space and consistent enrichment inside their confinement area.