Ringworm in cats is highly contagious. It spreads to other cats, dogs, and humans through direct contact with an infected animal or through contaminated objects like bedding, brushes, and furniture. The fungus responsible produces tiny spores that can survive on household surfaces for 12 to 20 months, making it one of the more persistent infections a pet can bring into a home.
How Ringworm Spreads
Over 90% of feline ringworm cases are caused by a fungus called Microsporum canis. This fungus produces microscopic spores (called arthrospores) that sit on the cat’s fur and skin, then transfer to anything the cat touches. You can pick it up by petting an infected cat, but you can also pick it up indirectly from contaminated furniture, carpeting, grooming tools, or clothing. The spores are light enough to drift onto surfaces the cat never directly touched.
The incubation period ranges from four days to four weeks. That means after exposure, it could take up to a month before you or another pet shows any signs of infection. During that gap, the fungus is already establishing itself and can be spreading further.
Cats Can Carry It Without Showing Symptoms
One of the trickiest aspects of feline ringworm is that many cats carry the fungus without ever developing visible lesions. These asymptomatic carriers look perfectly healthy but shed infectious spores from their coat. In one study of multi-cat households, nearly 17% of cats were asymptomatic carriers, and over half the households tested had at least one carrier cat. Cats older than six years were about 1.8 times more likely to be carriers than younger cats.
This matters because a cat that appears completely normal can still infect other pets and people in the home. If one animal in a household is diagnosed with ringworm, every other pet should be evaluated, even those without hair loss or skin changes.
Can Humans Catch It?
Yes. Ringworm is zoonotic, meaning it passes between animals and people. In humans, it typically appears as a red, circular, itchy rash on the skin, often on the arms, hands, or face (the areas most likely to contact a cat). Children, older adults, and people with weakened immune systems are the most vulnerable. The California Department of Public Health recommends that people in these higher-risk groups avoid all contact with an infected pet until treatment is complete.
For healthy adults, the risk is lower but still real. Washing your hands after handling a cat with ringworm helps, but because spores linger on surfaces, hand hygiene alone isn’t enough to prevent transmission in a shared living space.
How Long a Cat Stays Contagious
With aggressive treatment, an infected cat typically remains contagious for about three weeks. Without treatment, the contagious period lasts much longer, sometimes months, because the cat continues shedding spores into the environment. A cat is considered clear of the infection only after two consecutive negative fungal cultures, which are lab tests where a sample from the cat’s coat is checked for active fungal growth. These cultures are usually taken a few weeks apart, so the full process from diagnosis to confirmed clearance can take several weeks to a couple of months.
During treatment, isolating the infected cat to a single room that’s easy to clean (tile or hardwood floors rather than carpet) helps limit spore spread throughout the house.
Cleaning Spores From Your Home
Because fungal spores can survive on household surfaces for up to 20 months, environmental decontamination is just as important as treating the cat. Spores embed in carpet fibers, upholstery, curtains, and any soft material. Without thorough cleaning, a cat can be successfully treated and then become reinfected from its own environment.
Vacuuming daily in areas the cat has accessed removes a significant number of spores from carpets and furniture. Dispose of the vacuum bag or empty the canister outside after each use. Hard surfaces should be cleaned with a diluted bleach solution or a disinfectant labeled as effective against dermatophytes. Soft items like blankets, cat beds, and removable covers should be washed in hot water. Items that can’t be washed or disinfected, like heavily contaminated scratching posts, may need to be discarded.
Grooming tools, food bowls, litter boxes, and carriers used by the infected cat should all be disinfected or replaced. In multi-pet homes, keeping separate supplies for the infected cat prevents cross-contamination during the treatment period.
Which Cats Are Most at Risk
Kittens and cats with compromised immune systems are the most likely to develop active ringworm infections after exposure. Long-haired breeds tend to harbor more spores in their coats, which makes both detection and decontamination harder. Cats in shelters, catteries, or multi-cat households face higher exposure simply because they share space, grooming tools, and bedding with more animals.
Outdoor cats that interact with strays or wildlife have additional exposure routes. Some rarer fungal species that cause ringworm in cats are linked to contact with rodents or cattle, though these account for a small fraction of cases compared to the dominant Microsporum canis.