Symptoms and Treatment of Canine Fungal Dermatitis

Skin & CoatQ&AMeongsiljang Veterinary Advisory Board

Canine fungal dermatitis, also known as dermatophytosis, is a condition in which fungi infect the hair and skin. We’ve summarized the key symptoms—such as circular hair loss and dandruff—along with diagnosis, treatment, and home care methods, based on veterinary textbooks.

What Is Canine Fungal Dermatitis?

An illustration of a dog checking its skin condition

Canine fungal dermatitis is a contagious skin condition caused by dermatophyte fungi infecting the skin and hair, leading to circular hair loss and dandruff. Although commonly referred to as "ringworm," it has nothing to do with worms. Since it is a zoonotic disease that can be transmitted to humans, prompt diagnosis and treatment are essential.

Causative Fungi and Routes of Infection

According to veterinary dermatology textbooks, there are two primary fungal causes of canine fungal dermatitis.

Microsporum canis: This is the most common causative fungus in dogs and cats. Infection can occur through direct contact with an infected animal or indirectly via contaminated items such as combs, bedding, and blankets.

Trichophyton mentagrophytes: This is the second most common causative fungus in dogs and cats. Infection can result from both direct and indirect contact with various animals.

Fungal spores can survive in the environment for relatively long periods, meaning that spaces occupied by infected animals can themselves become sources of infection. Puppies with weakened immune systems, as well as those kept in overcrowded conditions or with poor nutritional status, are particularly susceptible.

Suspect Fungal Dermatitis If You See These Symptoms

Fungal dermatitis can present in various ways, making it easy to confuse with other skin conditions. Check for the following symptoms:

Circular hair loss: The most characteristic sign is hair falling out in a round pattern.

Dandruff and scaling: Significant dandruff often appears around the areas of hair loss.

Skin redness: The infected area may become red and raised.

Nail changes: Nails may become rough or brittle and prone to breaking.

Itching: While itching is often mild, some dogs scratch excessively.

Crusts and discharge: If a secondary bacterial infection develops, crusts or oozing may occur.

Illustration of a dog showing symptoms of fungal dermatitis

Comparison of Diagnostic Tests at Veterinary Clinics

Veterinary clinics diagnose fungal dermatitis through various tests, each with its own characteristics, allowing veterinarians to select the most appropriate method based on the situation.

Diagnostic Method	Characteristics	Time Required
Wood's lamp examination	Checks for fluorescence using an ultraviolet lamp	Immediate
Direct microscopic examination	Observes hair and skin samples under a microscope	Same day
Fungal culture test	Most accurate; can identify the specific causative fungus	1–3 weeks
PCR test	Fast and accurate, based on genetic analysis	Several days

A negative fluorescence result on a Wood's lamp examination does not rule out infection. While a characteristic apple-green fluorescence may be observed in Microsporum canis infections, a negative fluorescence result alone cannot completely exclude infection. Therefore, a comprehensive diagnosis is made in conjunction with fungal culture or PCR testing.

A Zoonotic Disease That Can Spread to Humans

Fungal dermatitis can spread from an infected dog to humans. Children, the elderly, and family members with weakened immune systems are at higher risk of infection. If your dog is diagnosed, avoid direct skin contact and always wash your hands thoroughly after handling them. If any family member develops circular red rashes on their skin, consult a dermatologist.

How Is It Treated?

Treatment for fungal dermatitis typically involves a combination of topical and oral medications.

Topical treatment: Antifungal shampoos or ointments are applied directly to the affected areas. In cases of systemic infection, the entire body should be bathed with an antifungal shampoo approximately twice a week. Topical treatment is the only method that directly removes infectious spores from the hair and skin surface, playing a role just as important as systemic therapy.

Oral treatment: Your veterinarian will prescribe antifungal medications (such as fluconazole or itraconazole) based on your pet’s weight and condition. These medications must be administered consistently for several weeks or longer. Even if symptoms appear to improve, stopping the medication prematurely can lead to recurrence.

It is important not to discontinue treatment based solely on symptom improvement. Therapy should continue until a fungal culture test confirms that the infection has been completely eradicated.

Illustration of a dog being bathed with antifungal shampoo.

How to Disinfect the Environment at Home

To prevent reinfection, it’s essential to combine treatment with thorough environmental management. Fungal spores can survive in the environment for a relatively long time, so disinfecting your pet’s living space is crucial.

Wash bedding and blankets: Launder frequently in hot water at 60°C or higher.

Disinfect floors and furniture: Wipe surfaces with a 1:10 diluted bleach solution.

Grooming care: Promptly clean up shed fur, and disinfect or replace grooming tools such as brushes.

Isolation: If you have other pets, limit contact during the treatment period.

Vacuuming: Frequently vacuum carpets and furniture, and dispose of dust bags immediately.

Illustration of a puppy resting in a clean environment

Key Points to Remember During Treatment

Fungal dermatitis can take weeks to several months to treat. Even if symptoms appear to improve, do not stop treatment until the fungal culture results are available. Stopping medication prematurely or reducing the dosage on your own can lead to recurrence. It is most important to complete the full course of treatment as directed by your veterinarian.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Can fungal dermatitis heal on its own?

In healthy adult dogs, the immune system can sometimes clear the infection on its own. However, recovery can take weeks to months, and during that time the disease can spread to other animals or people, so treatment is recommended.

What symptoms appear if it spreads to humans?

A circular rash with a red border and clear center may appear on the skin, sometimes accompanied by itching and flaky, scaly patches. If you notice these symptoms, please visit a dermatologist.

Are there certain dog breeds that are more prone to fungal skin infections?

Puppies with weak immune systems, dogs in poor nutritional condition, and those living in overcrowded environments are particularly vulnerable. Healthy adult dogs can usually fend off infections relatively well thanks to their immune systems, but when immunity is compromised, infections are more likely to occur and symptoms may persist longer. Therefore, it’s important to closely monitor puppies and dogs whose overall condition has declined.

How much does the treatment cost?

The cost varies depending on the extent of the infection, the duration of treatment, and the medications used. For an accurate estimate, we recommend consulting with your veterinarian after a diagnosis.

Can fungal dermatitis be prevented?

The basics are avoiding contact with infected animals and keeping your pet’s living environment clean. A balanced diet and appropriate exercise can also help boost their immune system.