Many medical terms are notorious for being confusing, but ringworm is undoubtedly one of the most misunderstood. Though people commonly assume this disease is caused by a parasite, ringworm in cats has nothing at all to do with worms. Ringworm in cats, also known as dermatophytosis, is caused by a fungal infection of the skin, most often caused by the fungus Microsporum canis,according to the Merck Veterinary Manual.
How Do Cats Get Ringworm?
The trouble with ringworm is that you really can't hide from it. Cat ringworm is caused by a fungal organism that lives just about anywhere in the environment. It is found in soil and thrives particularly in warm, humid environments. Ringworm agents aren't restricted to soil, though; the fungal spores are tiny enough that they can easily hitch a ride on blankets, clothing and fur and be transported indoors, where they can flourish as well.
Once the fungus finds a living food source, such as a cat, dog or human, it sets up shop in the hair follicle. It feeds on keratin, making hair, nails and skin its main nutritional sources. Here is where ringworm gets a little tricky; even if a cat becomes contaminated with the fungus, it doesn't mean they will always develop a ringworm infection, which is good news for pets and pet parents worldwide, said Cornell Feline Health Center.
Once on the cat, a meticulous self-groomer may simply rid the fungus from their coat. Other competitors, such as bacteria, thriving on the cat's skin may outnumber and defeat the fungus or the fungus may survive and stick around. While some cats can be asymptomatic when they are infected with ringworm, a number will develop clinical signs of infection.
What Are the Symptoms of Ringworm in Cats?
This is the only part of the name that warrants credit to those who coined the disease's name: ringworm often presents itself as a circular reddish rash — a ring — on the skin of an infected cat. Cats may begin to lose hair or develop a dull or stubby coat. Signs may progress to patchy hair loss, scaling or itchy skin and infected nails.

How Common Is Cat Ringworm?
While some diseases are rare, ringworm makes its rounds; it is perhaps the most frequently encountered infectious skin disease of cats worldwide. While it can affect any cat, kittens with less robust immune systems are more likely to develop an infection. Long-haired cat breeds are also more susceptible, along with cats in high-population settings (such as catteries), cats with other systemic diseases that may weaken their immune system or cats with poor nutrition.