Fungal infections on dogs typically show up as patchy hair loss, red or darkened skin, crusty sores, or greasy, flaky patches, but the exact appearance depends on which type of fungus is involved. The three most common categories are ringworm, yeast infections, and deep systemic fungal infections, and each one looks distinctly different on your dog’s skin.
Ringworm: Circular Patches of Hair Loss
Ringworm is the most recognizable fungal infection in dogs. Despite its name, it has nothing to do with worms. It’s caused by fungi that feed on keratin in the skin, hair, and nails. The hallmark sign is round patches of hair loss, usually 1 to 3 millimeters at first, that expand outward in a roughly circular shape. The edges of these patches are often scaly or crusty, while the center may look relatively clear, giving the classic “ring” appearance.
Beyond the circular bald spots, you may notice small red bumps, flaky crusts, or tiny pus-filled spots scattered around the lesion. The skin underneath the missing fur often looks reddened and irritated. Ringworm lesions tend to show up first on the face, legs, and tail, though they can appear anywhere. Some dogs carry the infection with only subtle scaling and no obvious hair loss, which makes it easy to miss in the early stages.
One thing worth knowing: the old trick of using a blacklight (Wood’s lamp) to detect ringworm only catches about 71% of cases. A negative glow doesn’t rule it out. Your vet will likely need to take a skin scraping or fungal culture for a definitive answer.
Ringworm spreads easily between dogs and people. If you suspect it, wear gloves when handling your dog, wash your hands thoroughly afterward, and vacuum areas where your dog spends time. On human skin, it produces the same ring-shaped rash.
Yeast Infections: Greasy, Smelly, Thickened Skin
Yeast dermatitis looks and smells very different from ringworm. It’s caused by an overgrowth of yeast that naturally lives on your dog’s skin, and it produces a strong, musty odor that many owners notice before they see any skin changes. The smell is often described as stale or sour, and it can be intense enough to fill a room.
Visually, yeast infections cause waxy, greasy-looking skin with yellow or slate-gray scales. As the infection progresses, the affected skin darkens and thickens into a leathery, wrinkled texture sometimes called “elephant skin.” The area is usually very itchy, so you’ll see your dog licking, scratching, or rubbing the affected spots constantly.
Ears
Yeast thrives in the warm, moist environment of the ear canal. Infected ears produce a thick, brown discharge with a strong odor. The ear canals look red and inflamed, and your dog may shake their head frequently or paw at the affected ear.
Paws
Between the paw pads is another favorite spot for yeast. Look for red, moist areas between the toes and a brownish discoloration of both the skin and surrounding fur. Dogs with paw yeast infections often lick their feet obsessively, which makes the problem worse by adding more moisture.
Skin Folds and Body
Yeast infections also commonly develop in skin folds around the neck, armpits, groin, and around the lips. Any area where skin stays warm and damp is vulnerable. Breeds with heavy skin folds, floppy ears, or allergies are especially prone.
Deep Fungal Infections: Sores That Won’t Heal
Systemic fungal infections like blastomycosis are less common but more serious. Dogs pick up these fungi by inhaling spores from contaminated soil, and the infection starts in the lungs before potentially spreading to the skin and other organs. On the skin, these infections produce raised, firm nodules or granular sores that may ulcerate and drain fluid. They tend to appear on the face, around the nose, and on the nail beds. Roughly 30% to 50% of dogs with blastomycosis develop these skin lesions. Unlike ringworm or yeast infections, these sores don’t respond to topical treatments and are usually accompanied by other signs of illness like coughing, fever, weight loss, or lethargy.
How Fungal Infections Differ From Mange
Several skin conditions in dogs mimic the look of a fungal infection, and mange is the most common source of confusion. Knowing the differences can help you describe what you’re seeing to your vet.
Demodectic mange causes hair loss and reddened, swollen skin that can look a lot like ringworm. The key differences: demodectic mange often produces acne-like bumps, darkened skin, and inflamed foot pads. It frequently triggers secondary bacterial infections that cause deeper, pus-filled inflammation. Dogs with widespread demodectic mange may also have swollen lymph nodes and fever.
Sarcoptic mange (scabies) starts as small, solid bumps on the abdomen, chest, ears, elbows, and legs. The intense itching drives dogs to scratch and bite so aggressively that the bumps quickly turn into thick, crusted sores. Over time, untreated scabies causes oily dandruff, severe skin thickening, and oozing wounds. The itching with scabies is typically far more intense than what you see with ringworm.
Walking dandruff, caused by a different mite, produces heavy flaking along the back. It looks more like severe dandruff than a fungal infection, but the scaling can be confused with the crusty patches of ringworm.
- Ringworm: circular bald patches with crusty edges, mild to moderate itching, often on face and legs
- Yeast infection: greasy, dark, thickened skin with a strong odor, intense itching, common in ears, paws, and skin folds
- Demodectic mange: patchy hair loss with acne-like bumps, darkened skin, inflamed feet, minimal itching early on
- Sarcoptic mange: small bumps that become thick crusts, extreme itching, starts on belly, chest, and elbows
What a Vet Visit Looks Like
Because so many skin conditions overlap visually, a vet visit is the only reliable way to confirm a fungal infection. For suspected ringworm, your vet will likely take hair samples or skin scrapings and send them for a fungal culture, which can take one to two weeks to come back. They may also examine the skin under a blacklight as a quick screening step, though this misses nearly a third of cases.
For yeast infections, diagnosis is usually faster. A vet can press a piece of tape or a glass slide against the affected skin, stain it, and look at it under a microscope to see the characteristic oval yeast organisms. Deep fungal infections require more involved testing, often including bloodwork, X-rays, or urine tests to check for systemic disease.
Treatment timelines vary. Localized yeast infections in the ears or on the skin often improve within a couple of weeks with topical antifungal therapy. Ringworm typically takes longer, sometimes six weeks or more of treatment before the infection fully clears and hair begins regrowing. If the inflammation has been severe or prolonged, some areas of hair loss from ringworm can become permanent. Deep fungal infections require months of oral medication and close monitoring.