Ringworm is a fungal infection that can affect a cats skin, hair, and nails. It is caused by a type of fungus known as a dermatophyte, and in cats, about 98% of ringworm cases are caused by the fungus Microsporum canis. Ringworm can be challenging to detect in cats since the lesions of ringworm may be very mild or even undetectable. However, some common symptoms of ringworm in cats include circular areas of hair loss, broken and stubbly hair, scaling or crusty skin, alterations in hair or skin color, inflamed areas of skin, excessive grooming and scratching, infected claws or nail beds, and dandruff.

If ringworm is suspected, a veterinarian will first attempt to exclude the presence of other dermatologic conditions that the infection may resemble, such as flea allergy. Toward this goal, the veterinarian may examine the cat’s coat with a Wood’s lamp—an ultraviolet light under which a fungus-coated hair will glow with a yellowish-green color. The hairs that fluoresce in this manner are then examined microscopically for specific spores and other fungal characteristics. If ringworm is diagnosed, treatment will typically involve the application of topical antifungal medications to all infected areas and, in most cases, a systemic medication as well. For treatment to be successful, all environmental contamination must also be eliminated. Ringworm can be transmitted quite easily to humans, particularly children, and it is important to take appropriate steps to minimize exposure to the fungus while the cat is being treated.