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Ringworm in Dogs

What is Ringworm in Dogs?

Ringworm in dogs isn’t a parasite as the name might suggest. Instead, it’s a fungal infection known for the circular, itchy rash it creates on the skin of affected animals. Ringworm, also called dermatophytosis medically, is caused by fungal organisms like Microsporum and Trichophyton, which feed on dead skin or hair cells. Though more commonly associated with cats, dogs and humans can also contract ringworm. It’s highly contagious and can be transmitted between pets and people, making it a zoonotic concern.

Symptoms and Types

Ringworm in dogs typically affects areas such as the face, ears, tail, and feet. Symptoms commonly include:

  • Circular patches of hair loss, often accompanied by a red and crusty perimeter
  • Hair breakage and an overall poor coat condition
  • Dry, scaly skin or patches with excessive dandruff
  • Skin inflammation
  • Darkened skin patches
  • Itchiness, frequent scratching, or excessive grooming
  • Inflamed nail beds or nails that appear darkened or dry
  • Nails that are dry, brittle, or misshapen


Ringworm in dogs is primarily contracted through direct contact with an infected animal, usually a dog or cat, or with a human. Dogs may harbor the ringworm fungus without showing outward signs but can still transmit the disease to other animals or people.

Additionally, ringworm can spread through contaminated objects like brushes, dog beds, toys, and surfaces that are challenging to clean, such as rugs, wool, and wood. Certain types of ringworm fungi reside in soil, and dogs may pick up the infection while digging, particularly in warm and humid environments. The spores of these fungi are resilient and can survive in the environment for up to 18 months.

Dogs with weakened immune systems, such as the very young or old, those with immune-suppressing illnesses, or those recently from kennels or shelters, are more susceptible to ringworm. Some breeds like Boston Terriers, Yorkshire Terriers, and Russell Terriers are genetically predisposed to ringworm infections.

Moreover, dogs with existing skin conditions are at higher risk. While the skin typically acts as a protective barrier, open wounds, fresh scratches, fleas, or chronic skin issues increase susceptibility to infection. Ringworm typically manifests with lesions on the skin appearing 1-3 weeks post-exposure, when spores attach to damaged skin.


Veterinarians employ several methods to diagnose ringworm in dogs, with common approaches including a Wood’s lamp examination, fungal culture, and PCR test.

A Wood’s lamp emits long-wave ultraviolet light, aiding in the detection of bacteria. The fungus Microsporum canis, often responsible for ringworm infections in pets, triggers a chemical reaction when it attaches to hair follicles, causing them to fluoresce under the Wood’s lamp. However, asymptomatic carriers won’t exhibit fluorescence.

This initial examination proves effective in about 72% of M. canis cases with active skin lesions, usually becoming visible 5-18 days post-infection. It serves as a valuable starting point when veterinarians suspect ringworm.

A fungal culture, also known as a dermatophyte test medium (DTM), involves collecting hair, scales, or scabs and placing them on a culture medium to allow fungal growth. Microscopic examination helps determine the presence of fungal species causing ringworm. Positive signs may appear after 3-5 days, with final results taking 10-21 days. Unlike the Wood’s lamp, this test doesn’t necessitate active skin lesions; any hair sample suffices.

PCR (Polymerase Chain Reaction) testing is a newer diagnostic tool for ringworm. It analyzes hair samples for fungal DNA, offering quicker results compared to culture methods, usually within 3-5 days. While PCR serves as an effective initial diagnostic tool, it can’t confirm complete clearance of the infection since it doesn’t distinguish between living and non-living fungal DNA. As such, fungal culture testing is typically recommended for follow-up to ensure complete eradication of the infection.


Treatment for ringworm in dogs is achievable and successful through adherence to comprehensive treatment, quarantine, and cleaning protocols. As ringworm can persist stubbornly, full commitment to the following procedures is crucial:


Upon suspicion of a ringworm infection, it’s imperative to quarantine the dog due to its highly contagious nature. Limiting contact with other pets and humans is essential. Ideally, quarantine the dog in a easily cleanable room such as a large bathroom, avoiding rugs or wood floors which are challenging to clean.

Topical Treatments (applied to the body)

Bathing plays a pivotal role in treatment by eliminating and killing fungal spores on the dog’s fur, preventing environmental and cross-contamination. Two main topical treatments are Lime Sulfur dips and antifungal shampoos, with Lime Sulfur dips being more effective. These can be administered at home or at a vet’s office, although many prefer the latter due to messiness and odor. Ointments or other topically applied medications aren’t proven effective against ringworm.

Oral Treatments (Medications taken by mouth)

Oral medications inhibit the reproduction and spread of the fungus, often used concurrently with topical treatments. Various oral antifungals exist, each with distinct costs and potential side effects, typically gastrointestinal-related. Veterinarians collaborate with pet owners to select the most suitable medication based on the pet’s health and diagnosis.

Decontamination Procedures

Infected pets continuously shed fungal spores, necessitating stringent isolation and thorough decontamination of the environment until culture tests turn negative or the vet advises discontinuation of treatment. All areas the dog has accessed should be meticulously cleaned and disinfected using effective agents like dilute bleach solution or accelerated hydrogen peroxide. Vacuuming and steam cleaning floors are crucial, while launderable items like dog beds should undergo hot water washing with bleach. The confined area should undergo biweekly cleaning during treatment, with caregivers wearing disposable gloves and practicing proper hand and clothing hygiene after handling infected pets.

Recovery and Prevention

It’s crucial to acknowledge that pets can harbor ringworm without showing symptoms, making them silent carriers. Consequently, if one pet is diagnosed with ringworm, all other pets in the household should be tested.

Treatment typically spans weeks to months and should only cease upon confirmation through follow-up testing that fungal organisms have been eradicated, as directed by the veterinarian. Ideally, to monitor treatment progress, fungal cultures should be conducted every 2-3 weeks post-treatment initiation.

Individuals infected with ringworm can transmit it to their pets. If you notice a red, ringed skin lesion, seeking medical evaluation from a doctor or healthcare professional is advisable.

When welcoming stray dogs or cats into your home, it’s vital to isolate them from resident pets until they undergo a thorough veterinary examination.

Given that ringworm can lurk in soil, preventing dogs from digging outside, especially in areas abundant with wildlife, helps mitigate the risk of infection.

Regular biannual veterinary exams for dogs prove beneficial. Pets with healthy skin are less susceptible to ringworm infections, underscoring the importance of proactive healthcare measures.

Ringworm in Dogs FAQs

How contagious is ringworm from a dog to a human?

Regrettably, ringworm can spread quite easily to humans. Those most vulnerable include individuals with weakened immune systems like young children, the elderly, pregnant women, and those undergoing chemotherapy or other immunosuppressive treatments.

Does ringworm in dogs disappear without treatment?

In theory, ringworm could resolve on its own within approximately 9-12 months, contingent upon the species of ringworm fungus and the dog’s immune system strength. However, during this period, the dog could contaminate its surroundings, potentially infecting humans and other pets in the household. Moreover, significant hair loss may occur as ringworm feeds on hair and dead skin, rendering the dog’s skin more susceptible to injuries and secondary infections.

How can I recognize if my dog has ringworm?

Various skin conditions may resemble ringworm. If you observe crusty lesions, circular patches of hair loss with red-ringed skin, or any persistent skin abnormalities that aren’t improving, it’s advisable to have your dog examined by a veterinarian for proper evaluation and treatment.

Are there home remedies for treating ringworm in dogs?

Numerous household remedies are rumored to treat ringworm, but they are ineffective and can even pose toxicity risks to pets. While certain over-the-counter antifungal shampoos may offer some relief, non-prescription medications aren’t consistently efficacious.

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