Despite the name, ringworm has nothing to do with worms. It is an infection of the skin, hair or claws caused by a type of fungus called a dermatophyte. [1] Vets call it dermatophytosis.
Ringworm matters for two reasons. It passes from animal to animal, and it can also pass from pets to people. [1][2] In many pets it would fade on its own, but that can take months, so vets usually treat it to protect the household. [1] The good news is that it is treatable, and according to the World Association for Veterinary Dermatology (WAVD) guidelines, serious health problems in people who catch it from animals are very rare. [2]
What causes ringworm in pets?
The fungi that most often infect cats and dogs belong to the groups Microsporum and Trichophyton. [1][2]
- In both cats and dogs, Microsporum canis causes most cases. It usually spreads by direct contact with an infected animal, most often a cat. [1]
- Other species include M. gypseum, which lives in soil, and Trichophyton mentagrophytes, which pets often pick up from rodents or their nests. [1]
- Shared objects such as brushes, collars and bedding can carry the fungus too, and its spores can survive in the home for months. [1]
Which pets are most at risk?
- Very young and older pets, and pets with a weakened immune system, are infected most often. [1]
- Crowded, poorly kept settings such as puppy mills, pet shops and catteries raise the risk. In an affected cattery, sometimes only the kittens show signs, and longhaired cats can keep the infection going. [1]
- Persian cats and Yorkshire Terriers seem more prone to widespread or deeper infections. [1]
- Some cats carry the fungus without any signs and can pass it on. [1]
Signs of ringworm
Ringworm does not always look like a neat ring. Signs vary a lot from pet to pet: [1]
- Dogs: the typical patch is a round bald spot with short, broken hairs, flaky skin and mild redness, which grows outward and may heal in the middle. Some dogs get several patches, small bumps or a firm, oozing lump. [1]
- Cats: bald patches with crusts and scale, most often on the face, ears and paws, though any part of the body can be affected. Some cats get many tiny crusted bumps. [1]
Itching differs too: it is common in cats and can be intense, while dogs with ringworm are usually not itchy. [1] (If your pet is itchy, see our guides to itchy dogs and itchy cats.) Ringworm can look like many other skin problems, and in dogs a bacterial skin infection is often mistaken for it, so a vet test is needed to confirm it. [1]
How vets diagnose ringworm
No single test is perfect, so vets usually combine several. [1][2]
- Wood’s lamp: under this ultraviolet light, hairs infected with M. canis often glow apple green or blue green. About 70% of cases glow, so a negative result does not rule ringworm out, and a positive one still needs other tests. [1]
- Looking at hairs under the microscope: your vet plucks broken hairs from the patch and checks them for fungal spores. [1]
- Fungal culture: grows the fungus to identify it and to track progress, but it can take up to 3 weeks before a culture can be called negative. [1]
- Other tests: a PCR test or, for unusual lumps, a skin biopsy. [1]
How ringworm is treated
The WAVD guidelines recommend combining two kinds of treatment: [2]
- Oral antifungal medication, to clear infection inside the hair follicles, and
- Topical treatment of the hair coat (medicated shampoos, rinses or dips), to kill fungal material on the hair and limit spread.
Topical treatment alone is usually not enough for cats, because it may not reach the part of the hair inside the follicle and some cats stay carriers. [1] Your vet may recommend clipping the hair around the patches so topical treatment reaches the skin. [1]
Ringworm can clear up by itself, but that may take months, and treating it lowers the risk of spread to other animals and people and helps your pet recover sooner. [1] Treatment usually lasts several weeks or longer. Your vet will repeat fungal cultures and keep treatment going until at least one, and ideally two, come back negative, so keep going until your vet says to stop. [1]
Can I catch ringworm from my pet?
Yes. The CDC says ringworm passes easily between people, pets and shared objects, and touching an infected pet is one way people catch it. [3] Spread from animals to people is the most common direction, but people can also pass it to pets. [1]
If your pet has ringworm, the CDC advises: [3]
- Take your pet to the veterinarian right away for treatment.
- Wear gloves and long sleeves when handling the pet.
- Wash your hands with soap and running water after contact.
- Vacuum the areas of the home the pet commonly visits.
Talk to your doctor if anyone in the home develops an itchy, red, ring-shaped rash, especially children or anyone with a weakened immune system.
Protecting other pets
- Keep the infected pet separate from other pets if your vet recommends it.
- Ask your vet whether other pets in the home should be checked or treated, since ringworm spreads between animals and some cats carry it without signs. [1][2]
- Ask your vet for advice on cleaning bedding, brushes and the home. The WAVD guidelines say thorough physical cleaning is the main step for clearing the fungus from a home. [2]
When to see your vet
Book a visit if your pet has:
- Patchy hair loss, especially with scaling, crusting or broken hairs
- Lesions on the face, ear tips, tail or feet
- A new kitten or puppy with skin patches
- Skin patches at the same time as a ring-shaped rash on a person in the home
Frequently asked questions
Is ringworm a worm?
No. It is a fungal infection of the skin, hair or claws caused by dermatophytes. [1]
How can I tell if my cat has ringworm?
Look for bald patches with crusts or flaky skin, often on the face, ears or paws, and watch for itching. [1] Only vet tests, such as a Wood’s lamp exam, a microscope check of the hairs or a fungal culture, can confirm it. [1]
Are kittens more likely to get ringworm?
Yes. Very young animals are among the most often infected, and in an affected cattery the kittens may be the only cats showing signs. [1]
Can ringworm go away on its own?
It often would in time, but that can take months. [1] Vets usually treat it with medicine by mouth plus topical coat treatment, which speeds recovery and lowers the risk of spread to people and other pets. [1][2]
How long does ringworm treatment take?
Usually several weeks or longer. Your vet will keep treatment going until follow-up fungal cultures are negative. [1]
Can my dog or cat give me ringworm?
Yes. The CDC says ringworm passes easily between people, pets and shared objects. [3] Wear gloves, wash your hands after contact and get your pet treated. [3] Serious health problems in people who catch it from pets are very rare. [2]
The bottom line
Ringworm is a common, contagious fungal skin infection of cats and dogs, most often caused by Microsporum canis, and kittens are especially prone. It is diagnosed with a combination of tests and treated with oral antifungals plus topical coat treatment for several weeks. Because people can catch it, simple hygiene steps protect your family while your pet recovers.
See your vet if your pet has patchy hair loss or scaly, crusted patches, and talk to your doctor if anyone in the home develops a ring-shaped rash.
This article is for general information only and is not a substitute for professional veterinary or medical advice, diagnosis or treatment. Always consult your veterinarian about your pet’s health, and your doctor about your own. If you think your pet has a medical emergency, contact your veterinarian or an emergency animal hospital right away.
Sources
- Torres SMF. Dermatophytosis: Dogs and Cats. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota, 2025 (CC BY 4.0). https://open.lib.umn.edu/animaldermatology/chapter/dermatophytosis-dogs-and-cats/
- Moriello KA, Coyner K, Paterson S, Mignon B. Diagnosis and treatment of dermatophytosis in dogs and cats: Clinical Consensus Guidelines of the World Association for Veterinary Dermatology. Veterinary Dermatology. 2017;28(3):266-e68. doi:10.1111/vde.12440. https://pubmed.ncbi.nlm.nih.gov/28516493/
- Centers for Disease Control and Prevention. Ringworm: causes and prevention. https://www.cdc.gov/ringworm/causes/index.html ; https://www.cdc.gov/ringworm/aboutemergingringworm/index.html