Treating a fungal infection in dogs depends on whether the infection is on the skin’s surface or has spread deeper into the body. Superficial infections like ringworm and yeast dermatitis typically clear with medicated shampoos and sometimes oral medication over a few weeks. Systemic infections, where fungal organisms have entered the lungs, bones, or other organs, require months of oral antifungal therapy and careful veterinary monitoring.
Superficial vs. Systemic Infections
Fungal infections in dogs fall into two broad categories. Superficial infections stay on the skin, ears, or nails. The most common are ringworm (a skin fungus that causes circular patches of hair loss) and yeast dermatitis (an overgrowth of naturally occurring yeast on the skin, especially in skin folds, ears, and between toes). These are uncomfortable and contagious in the case of ringworm, but rarely life-threatening.
Systemic infections are a different story. Fungi like Blastomyces, which is most common in the Ohio River Valley and east of the Mississippi, exist as spores in soil. Dogs inhale the spores, which travel to the lungs and convert into a yeast form that can spread to the lymph nodes, eyes, bones, and skin. Coughing, labored breathing, swollen lymph nodes, eye redness, and even blindness are common signs. These infections require aggressive, long-term treatment.
Getting the Right Diagnosis
Before starting any treatment, your vet needs to confirm which fungus is involved. For ringworm, the standard test is a fungal culture using a special growth medium. Results are typically available within 7 days for dogs. A newer option, PCR testing, can return results faster and has a sensitivity around 85% to 86% with specificity above 94%, meaning it’s quite reliable but can occasionally miss an infection. Your vet may use both methods or combine them with a Wood’s lamp exam (a UV light that causes some ringworm species to glow green).
For yeast dermatitis, diagnosis is usually simpler. A skin cytology, where your vet presses a slide or tape against the affected skin and examines it under a microscope, can reveal the characteristic peanut-shaped yeast organisms in minutes. Systemic infections like blastomycosis often require urine antigen tests, X-rays to check the lungs, or sometimes biopsy of affected tissue.
Treating Ringworm
Ringworm treatment combines topical therapy to reduce environmental contamination with oral medication to clear the infection from the inside. For topical treatment, lime sulfur dips are highly effective. The recommended concentration is 8 ounces per gallon of warm water, which is actually twice the concentration listed on most product labels. These dips are applied to the entire body, not just visible lesions, typically twice a week. They smell strongly of sulfur and will temporarily stain light-colored fur yellow, but they work.
For small, isolated patches, a 2% miconazole ointment applied directly to the lesion can help. Miconazole shampoo combined with chlorhexidine is another topical option, though it works best as part of a broader treatment plan rather than on its own.
Oral antifungal medication is necessary for most ringworm cases, especially when lesions are widespread. Itraconazole is a common first choice for dogs. Terbinafine is another effective oral option, particularly for stubborn or resistant cases. Treatment continues until fungal cultures come back negative, which typically takes several weeks to a couple of months. Stopping early because the skin looks better is one of the most common mistakes, as the fungus can still be present and active beneath apparently healthy skin.
Treating Yeast Dermatitis
Yeast dermatitis in dogs is driven by an overgrowth of yeast that naturally lives on the skin. It tends to flare in warm, moist areas: ears, groin, armpits, and between the toes. Dogs with yeast dermatitis are often intensely itchy, and the skin may appear greasy, thickened, or have a distinctive musty odor.
The strongest evidence supports using a shampoo containing 2% miconazole combined with 2% chlorhexidine, applied twice weekly. A 3% chlorhexidine shampoo used alone also has moderate evidence behind it. These medicated baths need to stay on the skin for at least 10 minutes before rinsing to be effective. For dogs with chronic or recurring yeast problems, continuing twice-weekly medicated baths even after the infection clears can help prevent flare-ups.
If topical therapy alone doesn’t control the problem, your vet may add oral antifungal medication. Equally important is identifying what’s causing the yeast to overgrow in the first place. Allergies, particularly food and environmental allergies, are the most common underlying trigger. Without addressing the root cause, yeast dermatitis tends to come back repeatedly.
Treating Systemic Fungal Infections
Systemic infections like blastomycosis require oral antifungal medication for a minimum of 3 months, and often longer. Treatment continues until there’s no evidence of active disease on follow-up testing and imaging. Itraconazole and fluconazole are the two drugs most commonly used for blastomycosis in dogs.
The outlook is reasonable but not guaranteed. Roughly 70% of dogs treated for blastomycosis achieve a clinical cure. However, about 1 in 5 treated dogs will experience a recurrence months or even years after treatment ends, so ongoing monitoring matters. Dogs that have eye involvement or widespread disease at the time of diagnosis generally have a tougher road to recovery.
During treatment, your dog will need regular blood work. Oral antifungal medications are processed by the liver, and they can cause liver enzyme levels to rise. Your vet will check these levels periodically throughout treatment and adjust the plan if values climb too high. These medications should also be avoided in pregnant dogs because they can cause birth defects in developing puppies.
What to Expect During Treatment
For superficial infections, most dogs start showing visible improvement within 2 to 3 weeks of starting treatment. The itching often decreases before the skin fully heals. Full resolution of ringworm typically takes 6 to 8 weeks, sometimes longer in dogs with weakened immune systems.
Systemic infections are a longer commitment. Three months is the minimum for blastomycosis, and some dogs need 6 months or more. You’ll likely notice energy and appetite improving before respiratory symptoms fully resolve. Follow-up visits every few weeks to monitor blood work and track the infection’s response are a normal part of the process.
Some dogs experience mild side effects from oral antifungals, most commonly decreased appetite, vomiting, or soft stool. These are usually manageable and don’t require stopping the medication, though your vet should know about them. Loss of appetite that persists or yellowing of the gums or whites of the eyes could indicate a liver problem and warrants a prompt call to your vet.
Preventing Reinfection and Spread
Ringworm spores are remarkably hardy and can survive in the environment for over a year. During treatment, wash your dog’s bedding in hot water at least twice a week. Hard surfaces can be cleaned with a diluted bleach solution. Vacuuming frequently helps remove contaminated hair and skin cells from carpets and furniture. Ringworm is also contagious to humans and other pets, so limiting contact with affected areas and washing your hands after handling your dog reduces the risk of spreading the infection.
For yeast dermatitis, keeping skin folds dry and maintaining a regular bathing schedule with medicated shampoo are the most practical preventive steps. Dogs with floppy ears benefit from routine ear cleaning, especially after swimming or baths. Systemic fungal infections aren’t contagious between dogs, but dogs that spend a lot of time digging in soil or exploring wooded, marshy areas in endemic regions are at higher risk of inhaling fungal spores.