Explainer

Ringworm in Dogs and Cats: Signs, Treatment and Cleaning

Ringworm is a fungal skin infection, not a worm. How it looks in pets, how it spreads to people, treatment, and how to clean your home to stop it coming back.

Updated October 2026 · 6 min read · By the Hushku editorial team · 1 sources

Short answer

Ringworm is a contagious fungal skin infection, not a worm. In pets it causes round patches of hair loss with scaly or crusty skin, and brittle fur and claws; some cats carry it with no signs. It spreads to people and other pets through contact and contaminated bedding. Treatment usually combines antifungal medicine and medicated washes for several weeks, plus thorough cleaning at home.

Key facts

Ringworm is a fungus, not a worm.
It spreads to people; a rash appears 4–14 days after contact.
Kittens, puppies and long-haired cats are most often affected.
Disinfect hard surfaces with diluted bleach (1/4 cup per gallon of water).

Definition

Ringworm (dermatophytosis) is an infection of the skin, hair and nails caused by fungi called dermatophytes, most often Microsporum canis in cats and dogs.

The name comes from the ring-shaped rash it can cause in people. In pets, it more often looks like patchy hair loss.

Kittens, puppies, long-haired cats (especially Persians), and animals in shelters or with weakened immune systems are most often affected. Fungal spores can survive in the environment for many months, so cleaning matters as much as treating the pet.

According to the California Department of Public Health, people develop an itchy, red, ring-shaped rash 4 to 14 days after contact, usually on the face, arms or legs. Children, older people and those with weakened immune systems are at higher risk.

Signs and symptoms

Round patches of hair loss, often on the head, ears and front legs
Scaly, crusty or red skin
Broken or brittle hairs
Rough or brittle claws
Usually only mildly itchy, if at all
Some cats carry it with no visible signs
In people: an itchy, red, ring-shaped rash

Causes and risk factors

Direct contact with an infected animal
Contaminated bedding, brushes, towels, furniture and carriers
Spores in soil (some types)
Young age, long coats, crowding and stress raise the risk

Treatment

Oral antifungal medicine, such as itraconazole or terbinafine
Medicated shampoos, dips or rinses (lime sulphur or miconazole and chlorhexidine) to reduce spores on the coat
Clipping long fur can help, but should be done gently to avoid spreading spores
Treatment continues for several weeks, until follow-up fungal tests are negative
Treating or testing other pets in the household, even if they look healthy

Prevention

Quarantine and check new pets before introducing them
Don't share brushes and bedding between pets during treatment
Wash hands after handling an infected pet

How it's diagnosed

Your vet may use a UV (Wood's) lamp, which makes some ringworm strains glow, but not all do. A fungal culture or PCR test of hairs confirms the diagnosis, and repeat cultures show when treatment can stop.

Cleaning your home

Confine your pet to an easily cleaned room during treatment. Vacuum often and throw away the bag or empty the canister outside. Wash bedding and towels in hot water. CDPH advises disinfecting hard surfaces with a fungicidal product or diluted bleach (1/4 cup per gallon of water), after first cleaning off hair and debris.

Protecting your family

Limit cuddling during treatment, wear gloves and long sleeves when handling your pet, and wash hands afterwards. Anyone with a suspicious rash should see a doctor and mention the pet's diagnosis; ringworm in people is usually easily treated.

Sources

California Department of Public Health: Ringworm and pets

We check guides against veterinary sources and update them when guidance changes. How we write and review.

Questions.

How long is a pet with ringworm contagious?

Until treatment has cleared the infection, which typically takes several weeks. Your vet will use follow-up tests to confirm.

Can ringworm go away on its own?

It can in healthy adult animals, but this takes months, during which the pet spreads spores. Treatment shortens the time and protects your family.

Is it called ringworm because of a worm?

No. It's a fungus. The name comes from the ring-shaped rash it causes in people.