Cat ringworm is not a worm — it is a fungal skin infection caused by dermatophytes, most commonly Microsporum canis. It creates circular, scaly, hair-loss patches that spread easily between cats, other pets, and people. Treatment requires patience: antifungal therapy typically continues for 6–10 weeks, and environmental decontamination is essential to prevent reinfection.
Last reviewed: June 2026
What Is Cat Ringworm?
Ringworm (dermatophytosis) is a superficial fungal infection of the hair shafts and skin caused by keratinophilic fungi. In cats, Microsporum canis accounts for over 90% of cases, with Trichophyton mentagrophytes responsible for most of the remainder. The infection is acquired through direct contact with infected animals, fomites (brushes, bedding, fabric), or contaminated soil.
Cats — especially kittens under 1 year, immunocompromised adults, and longhaired breeds (Persians, Maine Coons) — are particularly susceptible. As described in Greene's Infectious Diseases of the Dog and Cat, M. canis can survive on shed hairs in the environment for up to 18 months, which is why environmental decontamination is as important as treating the cat.
Ringworm is a zoonosis — humans, especially young children, elderly, and immunocompromised individuals, can contract it from infected cats. Any household member developing a circular, itchy skin lesion should see a physician.
Signs of Ringworm in Cats
Classic signs include:
- Circular patches of hair loss (alopecia) with a scaly, sometimes crusty border
- Broken hair shafts at the skin surface — the hallmark of dermatophyte invasion
- Erythema (redness) at lesion margins; the center may appear to heal while the edge spreads
- Dandruff-like scaling without obvious hair loss (common in mild cases)
- Facial lesions — nose, periocular area, and ears are frequent sites
- Pruritus (itch) — variable; many cats are minimally itchy
Some cats are asymptomatic carriers — apparently healthy but shedding infective spores. This is especially common in Persians and makes multicat households particularly challenging to clear. Per the AAFP-AAHA Feline Life Stage Guidelines, 2021, all cats in an affected household should be tested by fungal culture, not just visually affected ones.
Diagnosis
Wood's lamp fluorescence (bright apple-green glow under UV) is positive in approximately 50% of M. canis infections and is a quick in-clinic screen — but a negative result does not rule out ringworm. Fungal culture of plucked hairs and scale using a toothbrush technique on a dermatophyte test medium (DTM) is the gold standard, with results in 7–21 days. PCR testing is faster (1–3 days) and increasingly available.
Skin biopsy showing dermatophyte invasion of hair follicles is definitive but rarely necessary.
Treatment
Topical antifungals: Twice-weekly whole-body miconazole/chlorhexidine shampoo is the backbone of treatment. Lime sulfur dips (every 5–7 days) are highly effective in severe multicat households but are malodorous and can stain surfaces. Spot-treating lesions only is insufficient — spores extend beyond visible lesions.
Systemic antifungals: Itraconazole is the oral antifungal of choice in cats, typically dosed at 5 mg/kg PO every 24 hours or in pulse-dose protocols (1 week on / 1 week off). Per Plumb's Veterinary Drug Handbook, terbinafine is an alternative at 30–40 mg/kg PO SID; both drugs require periodic liver enzyme monitoring in prolonged courses. Treatment continues until two negative fungal cultures, obtained 2–4 weeks apart.
Environmental decontamination: Infected hairs shed by the cat carry viable spores. Daily vacuuming, steam cleaning of soft surfaces, and dilute bleach solution (1:10) on hard surfaces are necessary. Affected cats should be kept in easily cleaned rooms during treatment.
When to See a Vet
Call your vet today if:
- Your cat has spreading circular hair loss patches, especially on the face
- A family member (especially a child) has developed itchy ring-shaped skin lesions
- Your kitten has crusty facial lesions
- Multiple cats in the household are affected
Go to the ER immediately if:
- Your cat has rapidly spreading skin lesions with signs of secondary bacterial infection (pus, swelling, fever)
- An immunocompromised household member has extensive skin involvement
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Frequently Asked Questions
Is cat ringworm contagious to humans? Yes — ringworm is one of the most common zoonotic skin infections from pets. Transmission from cats to humans is well-documented, especially in children and immunocompromised adults. Household members handling an infected cat should wear gloves and wash hands thoroughly; those with symptoms should see a physician promptly.
How long does it take to cure ringworm in cats? With consistent treatment, most cases clear within 6–10 weeks. Multicat households and longhaired breeds typically take longer. Treatment is not complete until two negative fungal cultures, 2–4 weeks apart — visible lesion resolution alone is not sufficient, as the cat may still be shedding spores.
How much does treating ringworm in cats cost? A vet exam plus fungal culture runs $100–250. Oral itraconazole medication costs $50–120/month. Antifungal shampoos cost $20–50/bottle. Full treatment including all rechecks typically costs $300–700 for a single cat; multicat households can run $800–1,500 or more including environmental treatment costs.
Can I use over-the-counter antifungal cream on my cat? Human OTC antifungal creams are generally not effective for feline ringworm and should not be used without veterinary guidance — the infection penetrates the hair shaft and cannot be cleared by surface treatment alone. Additionally, cats will lick off topical products and some contain harmful ingredients.
Can an indoor-only cat get ringworm? Yes. Ringworm spores can be tracked into the home on shoes, clothing, or on other pets. Kittens adopted from shelters are a common source of introduction. Any new cat entering the home should be checked for ringworm before contact with resident cats.
Still Not Sure if Your Cat Needs a Vet?
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