Cats get ringworm by coming into contact with fungal spores, either directly from an infected animal or indirectly from contaminated surfaces, bedding, or grooming tools. Despite its name, ringworm has nothing to do with worms. It’s a fungal skin infection, and cats are one of the most common carriers.
The Fungus Behind the Infection
The overwhelming majority of feline ringworm cases are caused by a single fungal species called Microsporum canis. This fungus produces microscopic spores that attach to hair shafts and skin cells. Once the spores land on a cat, they can penetrate the outer layer of skin and begin feeding on keratin, the protein that makes up hair, nails, and the surface of the skin.
Less commonly, cats pick up other fungal species from specific animals they encounter. Contact with rodents can transmit different species of the fungus, and exposure to cattle can introduce yet another variety. But M. canis accounts for the vast majority of cases, especially in indoor and shelter environments.
Direct Contact With Infected Animals
The most common route of infection is direct physical contact with a cat, dog, or other animal that already carries the fungus. When an infected animal’s hair becomes brittle and breaks off, those tiny fragments are loaded with spores and spread easily during grooming, play, or even casual brushing against one another. This is why ringworm tears through shelters, catteries, and multi-cat households so quickly. Cat shows, boarding facilities, and mating introductions are all recognized risk factors.
What makes this especially tricky is that the animal spreading the infection doesn’t always look sick. In one study of 160 cats living in multi-cat households, nearly 17% were asymptomatic carriers, meaning they harbored the fungus on their coats without showing any visible skin lesions. Over half of the households tested had at least one carrier cat. A healthy-looking new cat brought into your home can silently introduce the fungus to every animal (and person) in the house.
Contaminated Objects and Surfaces
Cats don’t need to touch an infected animal to catch ringworm. The spores shed in broken hair fragments and skin flakes can land on bedding, furniture, carpet, scratching posts, brushes, food bowls, and cat carriers. M. canis spores are remarkably durable. They can remain infectious in the environment for up to a year under the right conditions.
This environmental persistence is a major reason ringworm is so hard to eliminate once it enters a home. A cat that never leaves the house can still develop ringworm if it lies on a couch, uses a brush, or sleeps in a bed that was previously contaminated. It also explains why reinfection is common. Even after a cat is successfully treated, leftover spores in the home can restart the cycle.
Which Cats Are Most Vulnerable
Any cat can get ringworm, but some are significantly more susceptible. Kittens are at higher risk because their immune systems are still developing. Cats that are stressed, malnourished, or dealing with other illnesses also have a harder time fighting off the fungus before it establishes an infection. Long-haired breeds are often cited as more prone, partly because their dense coats can trap and harbor more spores.
Interestingly, one study found that older cats (over six years) were 1.8 times more likely to be asymptomatic carriers than younger adults. Factors like breed, sex, coat length, and whether the cat was neutered didn’t significantly affect carrier status. This suggests that immune function and age play a bigger role than physical characteristics in determining which cats silently harbor the fungus.
How Quickly Infection Develops
After a cat is exposed to ringworm spores, the incubation period ranges from four days to four weeks. During this window, the fungus is colonizing hair follicles and skin but hasn’t yet produced visible symptoms. A cat in this early stage can already be shedding spores and spreading the infection to other animals and people in the household before anyone knows there’s a problem.
The first visible signs are typically small patches of hair loss, often circular, with scaly or crusty skin underneath. Lesions commonly appear on the face, ears, and paws, though they can show up anywhere. Some cats develop only mild, easy-to-miss patches, while others lose hair in large areas. The severity depends on the cat’s immune response and how heavy the initial exposure was.
Outdoor Cats and Soil Exposure
Cats that spend time outdoors face additional exposure routes. Some ringworm-causing fungi live naturally in soil, and cats can pick up spores while digging, rolling, or simply walking through contaminated ground. Outdoor cats are also more likely to encounter infected wildlife. Hunting or close contact with rodents is a recognized source of certain fungal species that cause ringworm in cats.
Spread to Humans and Other Pets
Ringworm is zoonotic, meaning it passes between animals and humans. Cats are actually the primary source of M. canis infections in people. You can catch it by petting, holding, or grooming an infected cat, or by touching contaminated surfaces in your home. The same spore-laden hair fragments that spread the infection between cats are just as effective at infecting human skin.
Children, elderly adults, and anyone with a weakened immune system are most at risk. If your cat is diagnosed with ringworm, every person and pet in the household has potentially been exposed. Dogs, rabbits, and other mammals in the home are also susceptible. Because spores survive so long on surfaces, thorough cleaning of the home environment is just as important as treating the infected cat. Washing bedding in hot water, vacuuming frequently to remove contaminated hair, and disinfecting hard surfaces all help reduce the spore load and break the cycle of reinfection.