If you notice circular bald patches on your cat's skin, broken hairs around the face or ears, or scaly crusty spots developing on their coat, ringworm may be the culprit. Despite its ominous name, ringworm isn't caused by a worm at all — it's a fungal infection that affects the skin, hair follicles, and sometimes nails. It's also one of the relatively few pet health conditions that can readily spread to humans and other pets, making prompt identification and treatment important for the whole household.
What Is Ringworm?
Ringworm in cats — formally called dermatophytosis — is caused by a group of microscopic fungi called dermatophytes. The most common species in cats is Microsporum canis, though Trichophyton and Microsporum gypseum can also be responsible (AAFP-AAHA Feline Life Stage Guidelines, 2021). These fungi feed on keratin, the protein found in hair, skin, and nails. As they invade hair follicles and the outer layers of skin, they cause hair to break off and fall out in the characteristic patterns owners notice.
The name "ringworm" comes from the ring-shaped, scaly lesion the infection sometimes produces in humans — cats don't always develop this classic ring shape, and their lesions often look irregular.
How Cats Get Ringworm
Ringworm spreads through:
- Direct contact with an infected cat, dog, rabbit, or person
- Contact with contaminated objects — bedding, grooming tools, furniture, carpet, and clothing can harbor fungal spores
- Environmental exposure — Microsporum canis spores can survive in the environment for up to 18 months under the right conditions, making thorough decontamination essential
Kittens, elderly cats, and immunocompromised cats are significantly more susceptible than healthy adult cats. In shelters and multi-cat households, ringworm outbreaks can spread rapidly and are challenging to fully eradicate.
Signs of Ringworm in Cats
One of the most important things to know is that some cats — particularly healthy adult cats — are asymptomatic carriers. They carry the fungus and can actively spread it to people and other pets without showing any visible signs themselves. When symptoms are present, they typically include:
- Circular or irregularly shaped bald patches, most commonly appearing first on the head, face, ears, and front legs
- Broken or stubby hairs at the margins of lesions — the hair doesn't completely fall out but breaks off close to the skin surface
- Scaly, crusty, or slightly inflamed skin within the bald areas — the skin may appear dry, flaky, or reddened
- Brittle, distorted, or abnormally shaped claws in some cases — fungal infection of the nail bed
- Variable itching — some cats scratch intensely at affected areas, while others show no apparent discomfort
Ringworm in Multi-Cat Households
In households with multiple cats, ringworm often spreads to other cats before the first case is even noticed. If one cat is diagnosed, all animals in the home should be examined and potentially tested, even if they appear healthy.
When To Contact Your Vet
Contact your vet promptly if you notice:
- Any suspicious bald patches or scaly skin in your cat — ringworm must be confirmed through diagnostic testing, either a fungal culture (the gold standard), a Wood's lamp examination (ultraviolet light causes some — but not all — ringworm species to fluoresce green), or microscopic examination of hair samples
- Ring-shaped, itchy, red lesions appearing on human family members — this confirms active transmission and requires treatment for everyone affected
- Rapid spread of lesions across your cat's body
- Signs in a very young kitten or a cat with known immune system issues — these cats may develop widespread, severe infection
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What To Do at Home
Ringworm almost always requires veterinary treatment and a comprehensive home decontamination strategy running in parallel:
- Isolate the affected cat from other pets and limit contact with people, especially children and immunocompromised family members, until a definitive diagnosis is made and treatment is underway.
- Wash hands thoroughly after handling your cat or their belongings, before touching your face or others.
- Vacuum all soft surfaces daily and wash bedding, cat trees, and soft toys at the highest temperature tolerated by the fabric.
- Disinfect hard surfaces with a diluted bleach solution (1 part bleach to 10 parts water) — this is one of the most effective ways to kill fungal spores on surfaces.
- Follow the full course of treatment prescribed by your vet — antifungal shampoos, lime sulfur dips, or oral antifungal medication are typically required. Stopping treatment early because the cat looks better is a common reason for relapse.
- Do not apply human antifungal creams without veterinary guidance — the concentration, formulation, and safety profile differ between species.
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