Condition Guide

Cat Ringworm: Symptoms, Treatment, and How It Spreads to Dogs

By Emiel Maddens · Reviewed in consultation with licensed veterinary professionals · Updated April 2026 · 11 min read

Cat with circular patch of hair loss on its ear consistent with ringworm infection

Key Takeaways

Ringworm in cats is caused by the fungus Microsporum canis, not an actual worm, and it produces circular patches of hair loss with scaling and crusting.
Ringworm is zoonotic, meaning it can spread from cats to dogs and humans through direct contact or contaminated environments.
Kittens, elderly cats, and immunocompromised individuals (both feline and human) are at the highest risk for contracting and developing severe ringworm infections.
Diagnosis involves Wood's lamp screening, fungal culture on dermatophyte test medium, and sometimes PCR testing for faster confirmation.
Treatment requires both systemic antifungal medication (itraconazole or terbinafine) and topical therapy, typically for 6 to 8 weeks minimum.
Environmental decontamination with dilute bleach is essential to eliminate fungal spores from the home and prevent reinfection.

Ringworm is one of the most common infectious skin diseases in cats, and despite its name, it has nothing to do with worms. The condition is caused by dermatophyte fungi, primarily Microsporum canis, that invade the outer layers of skin, hair, and sometimes nails. What makes ringworm particularly concerning is its ability to spread between species, moving easily from cats to dogs, other pets, and humans.

Understanding how ringworm spreads, how to recognize it early, and how to treat it effectively is essential for any cat owner, especially those in multi-pet households. This guide covers the complete lifecycle of a feline ringworm infection, from initial exposure through diagnosis, treatment, and environmental cleanup. Whether your cat has just been diagnosed or you are trying to prevent an outbreak, this article provides the veterinary-backed information you need.

What Is Cat Ringworm?

Ringworm is a superficial fungal infection of the skin caused by a group of fungi called dermatophytes. In cats, the overwhelming majority of infections are caused by Microsporum canis, with Trichophyton mentagrophytes and Microsporum gypseum accounting for a smaller percentage of cases.

Microsporum canis Infection

M. canis is responsible for over 90% of ringworm cases in cats. The fungus produces enzymes called keratinases that break down keratin, the structural protein in hair and skin. This allows the fungus to colonize hair shafts and the outer skin layer (stratum corneum), causing the characteristic circular lesions and hair loss.

Carrier State

Some cats, particularly long-haired breeds, can carry M. canis on their coat without showing any clinical signs. These asymptomatic carriers are a significant source of infection for other animals and humans. Studies of catteries and shelters have found carrier rates as high as 30% in some populations.

Zoonotic Transmission

Ringworm is one of the most common zoonotic diseases transmitted from cats to humans. Infected cats shed fungal spores (arthrospores) into the environment, where they can survive for 18 months or longer on surfaces, bedding, and furniture. Humans typically develop red, itchy, ring-shaped lesions on exposed skin areas.

Veterinarian using a Wood's lamp to examine a cat for ringworm fluorescence

How Do Cats Get Ringworm?

Ringworm spreads through direct contact with infected animals or contaminated environments. Several factors increase a cat's susceptibility to infection.

1. Direct Contact with Infected Animals

The most common route of transmission is direct contact with an infected cat, dog, or other animal. Kittens in shelters, catteries, and breeding facilities are at particularly high risk due to close quarters and shared resources. Even brief contact can transfer enough fungal spores to establish an infection.

2. Contaminated Environment

Fungal spores shed from infected animals can persist on surfaces, bedding, grooming tools, and furniture for over 18 months. Cats can contract ringworm simply by resting on a contaminated surface or using a shared litter box. This environmental persistence makes ringworm outbreaks difficult to control without thorough decontamination.

3. Compromised Immune System

Cats with weakened immune systems, whether from age (very young kittens or senior cats), concurrent illness (such as FIV or FeLV), malnutrition, or immunosuppressive medications, are far more susceptible to ringworm. A healthy adult cat's immune system can often resist or quickly clear a minor fungal exposure.

4. Coat Type and Grooming

Long-haired cats, particularly Persians and Himalayans, are more prone to ringworm because their dense coats trap fungal spores and provide the warm, humid microenvironment that dermatophytes need to thrive. Normal grooming may not be sufficient to remove spores from deep within a thick coat.

5. Skin Barrier Disruption

Any damage to the skin's protective barrier, whether from scratches, flea bites, or pre-existing skin conditions, provides an entry point for dermatophyte fungi. Cats with concurrent skin problems are at increased risk of developing ringworm as a secondary infection.

Which Breeds Are Most Affected?

Certain cat breeds have documented higher susceptibility to ringworm due to their coat characteristics, immune tendencies, or genetic predispositions.

Persian: Persians have the highest breed-related incidence of ringworm among domestic cats. Their long, dense coats trap fungal spores and are difficult to fully decontaminate. Persians are also more likely to become asymptomatic carriers, spreading infection without showing obvious signs.
Himalayan: As close relatives of Persians with similar coat characteristics, Himalayans share the same elevated ringworm risk. Their flat facial structure can also make facial lesions more difficult to detect early.
Devon Rex: Devon Rex cats have sparse, fine coats that provide less mechanical protection against fungal colonization. Their skin is more directly exposed to environmental contaminants, and they may develop more widespread lesions than cats with denser fur.
Maine Coon: Maine Coons' long, thick coats create the same humid microenvironment that favors fungal growth seen in Persians. Their large body size also means more surface area for potential spore attachment and colonization.

Signs and Symptoms

Ringworm symptoms in cats range from subtle to severe. Some cats show classic circular lesions, while others may present with more diffuse signs that mimic other skin conditions.

Circular Patches of Hair Loss

The classic presentation of ringworm is one or more circular to irregularly shaped areas of hair loss, typically 1 to 3 centimeters in diameter. The edges of the lesion may appear slightly raised and more inflamed than the center, creating the 'ring' appearance that gives the condition its common name.

Scaling and Crusting

Affected areas often develop fine, white-to-gray scales and thin crusts. The skin may appear dry and flaky, similar to dandruff but localized to specific patches. In some cats, the crusting can become thick and adherent.

Broken Hair Shafts

Rather than complete baldness, some ringworm lesions show patches of short, broken hair stubs. The fungus weakens the hair shaft, causing it to snap off at or near the skin surface. These broken hairs are highly infectious and full of fungal spores.

Claw Infections (Onychomycosis)

In some cases, dermatophytes can infect the claws, causing them to become thickened, brittle, misshaped, and discolored. Claw infections are more resistant to treatment and may take longer to resolve than skin lesions.

Diffuse Hair Loss Without Obvious Lesions

Some cats, especially long-haired breeds, may develop generalized thinning of the coat without the classic circular patches. This presentation can be easily confused with other causes of hair loss, making fungal culture essential for accurate diagnosis.

Miliary Dermatitis Pattern

Occasionally, ringworm triggers a miliary dermatitis reaction with small, crusty bumps scattered across the body. This atypical presentation makes it important to include ringworm in the differential diagnosis for any cat with miliary lesions.

Diagnosis

Accurate diagnosis of ringworm is essential because treatment is prolonged and involves both the patient and the environment. Multiple diagnostic methods may be needed to confirm or rule out the infection.

Wood's Lamp Screening

The Wood's lamp emits ultraviolet light at a wavelength of approximately 365 nanometers. Some strains of M. canis produce a metabolite called pteridine that fluoresces bright apple-green under this light. However, only about 50% of M. canis strains fluoresce, so a negative Wood's lamp result does not rule out ringworm. It is best used as a quick screening tool to guide sample collection for culture.

Fungal Culture (Dermatophyte Test Medium)

Fungal culture on DTM is considered the gold standard for ringworm diagnosis. Hair and scale samples from the lesion margins are placed on the medium and monitored for 10 to 21 days. A positive result shows a characteristic color change from yellow to red, along with white, fluffy colony growth. Microscopic examination of the colony confirms the species.

PCR Testing

Polymerase chain reaction (PCR) testing can detect dermatophyte DNA in hair and skin samples within 24 to 48 hours, much faster than fungal culture. PCR is highly sensitive and specific, making it useful for rapid diagnosis and for screening cats in outbreak situations. The main drawback is higher cost.

Direct Microscopy (KOH Prep)

Hair samples can be cleared with potassium hydroxide (KOH) and examined under a microscope for fungal elements (hyphae and arthrospores) within and around the hair shaft. While this provides quick results, it requires experience to interpret and has a lower sensitivity than culture or PCR.

Treatment

Treating ringworm in cats requires a multi-pronged approach: systemic antifungal medication to eliminate the infection from within, topical therapy to reduce environmental contamination, and environmental decontamination to prevent reinfection.

Itraconazole (Systemic Antifungal)

Itraconazole is currently the preferred systemic antifungal for treating ringworm in cats. It is given orally, typically at a dose of 5 mg/kg once daily, often in a pulse dosing schedule (one week on, one week off). It is well-tolerated by most cats, though liver enzyme monitoring is recommended during prolonged treatment.

Terbinafine (Alternative Systemic)

Terbinafine is an effective alternative to itraconazole, given at 30 to 40 mg/kg once daily. Some dermatologists prefer terbinafine for its fungicidal (rather than fungistatic) activity. It has fewer drug interactions than itraconazole but can occasionally cause gastrointestinal side effects.

Topical Antifungal Therapy

Topical treatments reduce the number of infectious spores shed into the environment. Lime sulfur dips (applied twice weekly) are highly effective and are the topical treatment of choice recommended by veterinary dermatologists. Miconazole-chlorhexidine shampoos and enilconazole rinses are alternatives for cats that do not tolerate dipping.

Environmental Decontamination

Fungal spores can survive for 18 months or longer on surfaces. Effective decontamination requires twice-weekly cleaning of all surfaces with a 1:10 dilution of household bleach (sodium hypochlorite). Bedding should be washed in hot water with bleach, and heavily contaminated items like cat trees may need to be discarded.

Monitoring and Cure Confirmation

Treatment should continue until two consecutive negative fungal cultures, taken at least two weeks apart, confirm that the infection has been cleared. Stopping treatment based on visual improvement alone is a common mistake that leads to relapse. Most cats require 6 to 8 weeks of treatment, though some cases may take longer.

Supporting Skin Health During Ringworm Recovery

A healthy diet supports your cat's immune system as it fights ringworm. Scan your cat's food with the Vetified Ingredient Scanner to ensure it provides optimal nutrition for skin health and immune function during recovery.

Check Your Cat's Food

Prevention

Preventing ringworm requires a combination of hygiene, environmental management, and immune support, especially in multi-pet households or homes with immunocompromised individuals.

Quarantine New Animals

Any new cat entering a household, especially from a shelter or cattery, should be quarantined for at least two weeks and ideally screened with a fungal culture before being introduced to resident pets. This single step can prevent outbreaks in multi-cat households.

Regular Grooming and Inspection

Regularly brushing your cat and inspecting the skin during grooming sessions helps detect early lesions before they become widespread. Pay special attention to the face, ears, and paws, where ringworm lesions commonly first appear.

Environmental Hygiene

Regular cleaning of bedding, grooming tools, and surfaces reduces fungal spore load. In high-risk environments like catteries, using washable bedding and non-porous surfaces makes decontamination more effective.

Immune System Support

Maintaining overall health through proper nutrition, parasite prevention, and veterinary care helps the immune system resist fungal infections. Cats with chronic illnesses should be monitored more closely for skin changes.

Related Symptoms

Dogs with this condition often show these symptoms. Our guides explain each one:

Ringworm in Dogs, Understand how ringworm presents and is treated in dogs, including differences from feline infections.
Fungal Skin Infections in Dogs, A broader look at fungal skin diseases that affect dogs, with overlap to feline dermatophytosis.
Dog Hair Loss: Causes and Treatment, Hair loss from fungal infection is just one of many causes. Compare the differential diagnosis across species.

Frequently Asked Questions About Cat Ringworm

Q: Can I catch ringworm from my cat?

Yes, ringworm caused by Microsporum canis is zoonotic and readily transmits from cats to humans. You can contract it through direct contact with an infected cat or by touching contaminated surfaces and objects. People with weakened immune systems, children, and the elderly are at higher risk. If you develop red, itchy, ring-shaped skin lesions, see your doctor promptly.

Q: How long is a cat with ringworm contagious?

A cat with ringworm remains contagious throughout the course of infection and until treatment achieves cure. Even after lesions begin to resolve visually, the cat may still be shedding infectious spores. A cat is considered non-contagious only after two consecutive negative fungal cultures taken during treatment.

Q: Can ringworm go away on its own in cats?

In healthy adult cats with intact immune systems, mild ringworm infections can sometimes self-resolve over several months. However, treatment is strongly recommended because untreated cats shed enormous numbers of spores into the environment, putting other pets and human family members at risk. Treatment also speeds recovery and prevents the infection from spreading to other body areas.

Q: Is griseofulvin still used to treat ringworm in cats?

Griseofulvin was historically the standard treatment for feline ringworm, but it has largely been replaced by itraconazole and terbinafine due to their superior safety profiles. Griseofulvin can cause serious side effects in cats, including bone marrow suppression and teratogenicity (birth defects), and should never be given to pregnant cats or kittens.

Q: How do I clean my house after a ringworm diagnosis?

Thorough environmental decontamination is essential. Vacuum all carpets, furniture, and fabric surfaces daily and dispose of the vacuum bag or empty the canister outside. Wash all bedding, blankets, and washable items in hot water with bleach. Wipe hard surfaces with a 1:10 bleach dilution twice weekly. Discard heavily contaminated items that cannot be effectively cleaned, such as old cat trees or cardboard scratchers.

Q: Can my dog catch ringworm from my cat?

Absolutely. Microsporum canis readily spreads between cats and dogs. If your cat is diagnosed with ringworm, all dogs in the household should be examined by a veterinarian and potentially screened with fungal culture. Keeping the infected cat isolated from other pets during treatment is important to prevent cross-species spread.

Sources

Moriello KA, Coyner K, Paterson S, Mignon B. Diagnosis and treatment of dermatophytosis in dogs and cats: Clinical Consensus Guidelines of the World Association for Veterinary Dermatology. Veterinary Dermatology. 2017;28(3):266-e68.

DeBoer DJ, Moriello KA. Humoral and cellular immune responses to Microsporum canis in naturally occurring feline dermatophytosis. Journal of Medical and Veterinary Mycology. 1993;31(2):121-132.

Moriello KA. Feline dermatophytosis: aspects pertinent to disease management in single and multiple cat situations. Journal of Feline Medicine and Surgery. 2014;16(5):419-431.