Skin infections and parasitic skin conditions are among the most common presentations in small animal practice. For more about parasite prevention for dogs, see our detailed guide. In many cases, they appear together — a pet with an underlying allergy develops a secondary bacterial infection, or a mange mite infestation creates a damaged skin environment that bacterial colonization takes over. Understanding the individual conditions is essential for making sense of why treatment plans can be layered and prolonged.
Bacterial Skin Infections (Pyoderma)
Pyoderma — literally "pus in the skin" — is a bacterial skin infection, most commonly caused by Staphylococcus pseudintermedius in dogs and Staphylococcus felis in cats. Bacteria are a normal part of the skin's resident microbiome; pyoderma develops when the skin barrier is disrupted (by scratching, moisture, or a wound) and bacteria proliferate beyond their normal balance.
Surface and superficial pyoderma
Most pyodermas involve the superficial layers of the skin. They appear as pustules (small white or yellow raised spots), crusts, epidermal collarettes (circular scaling remnants of ruptured pustules), and areas of redness. In dogs with short coats, an active bacterial infection sometimes causes tufting — hair standing up in small clusters over infected follicles.
Hot spots (acute moist dermatitis) are a form of surface pyoderma — rapidly spreading, moist, painful skin lesions usually triggered by self-trauma at a single site.
Deep pyoderma
When infection penetrates through the hair follicle into deeper skin tissue (furunculosis and cellulitis), it becomes more serious. Deep pyoderma produces draining tracts, firm nodules, and significant pain. It's more common in certain breeds (German Shepherds are notably predisposed) and in immunosuppressed animals. Treatment requires systemic antibiotics for an extended course.
Diagnosis and treatment
Cytology — examining a skin impression smear under a microscope — confirms bacterial infection and identifies whether rods, cocci, or yeast are present. This guides treatment choice.
Superficial pyoderma typically requires three to four weeks of appropriate antibiotic therapy. Deep pyoderma requires six to eight weeks minimum, and resolution must be confirmed by clinical assessment rather than just symptom improvement — that's consistent with the International Society for Companion Animal Infectious Diseases' antimicrobial guidelines, which call for re-examination at two to three weeks in and continued treatment well beyond the point where the lesions look resolved.
Topical antibacterial therapy (medicated shampoos, wipes, or sprays) is often used adjunctively to reduce the bacterial burden on the skin surface.
Antibiotic resistance — particularly methicillin-resistant Staphylococcus pseudintermedius (MRSP) — is an increasing concern in veterinary dermatology. Cultures and sensitivity testing are recommended for recurrent or treatment-resistant pyoderma.
Yeast Dermatitis (Malassezia Dermatitis)
Malassezia pachydermatis is a yeast that lives on the skin and in the ear canals of healthy dogs. When skin conditions change — with increased moisture, lipid availability, or immune alterations — this yeast can proliferate and cause a distinctive inflammatory response.
Yeast dermatitis has a characteristic appearance: greasy, reddish-brown discoloration of the skin, and a rancid or "corn chip" odor. Common locations are skin folds, the groin, armpits, between the toes, and the ear canals. Affected dogs are intensely itchy, and the discoloration from chronic yeast is often visible as a rusty staining of white or light-colored fur.
Breeds with skin folds (English Bulldogs, Basset Hounds, Shar Peis) are predisposed because folds create warm, moist, poorly-ventilated microenvironments ideal for yeast.
Diagnosis is by skin cytology — Malassezia organisms are peanut-shaped yeast cells with a distinctive appearance. Treatment involves topical antifungal therapy (medicated shampoos, wipes, mousse) and systemic antifungal medication for more extensive cases. Underlying causes — usually allergy — must also be addressed, or the yeast infection will recur.
Ringworm (Dermatophytosis)
Despite the name, ringworm is not caused by a worm — it's a fungal infection caused by dermatophytes, most commonly Microsporum canis in dogs and cats. The "ring" refers to the classic expanding circular lesion seen in humans; pets don't always produce this classic ring pattern.
In cats, ringworm lesions are often circular areas of scaling and hair loss with a scaly, sometimes crusty surface. In dogs, lesions may be circular or irregular, with hair loss, scaling, and occasionally pustules. Some infected cats are "silent carriers" — they carry and shed the fungus without showing obvious skin signs.
Ringworm is zoonotic — it can spread from pets to people (and vice versa). Household members with scaling, ring-shaped skin lesions appearing after contact with an infected pet should consult a physician.
Diagnosis is by fungal culture, Wood's lamp examination (some strains fluoresce under UV light, though not all), or PCR testing. Treatment requires antifungal medications — topical for localized cases, systemic for widespread infections or multi-pet households. Environmental decontamination is critical because ringworm spores can survive in the environment for months.
Mange
Mange refers to skin disease caused by mites that live on or within the skin.
Sarcoptic mange (scabies)
Caused by Sarcoptes scabiei var. canis, sarcoptic mange is intensely itchy and highly contagious between dogs and to humans (though it's self-limiting in people without a dog host). The mite burrows into the superficial skin layer, producing a severe hypersensitivity reaction in most infected individuals.
Classic presentation: intense scratching, crusting and hair loss starting at the ear margins, elbows, hocks, and ventral abdomen. A "pinnal-pedal reflex" — the dog reflexively scratches when the ear margin is rubbed — is highly suggestive.
Diagnosis is challenging because mites are often too few to find on skin scraping. Serologic testing (blood test for mite antibodies) and response to treatment are often more reliable than direct demonstration of the mite. Treatment involves appropriate anti-parasitic therapy and environmental considerations.
Demodectic mange
Caused by Demodex canis mites, which are a normal resident of dog skin, present in very small numbers in most dogs without causing disease. Problems arise when immune regulation fails to keep the mite population in check.
Localized demodectic mange (common in puppies) appears as small patches of hair loss without much itch, usually on the face. Most resolve without treatment as the puppy's immune system matures.
Generalized demodectic mange is more serious — widespread hair loss, secondary infection, and systemic immune dysregulation. It requires sustained treatment and investigation for underlying immunosuppressive conditions, particularly in adult-onset cases — a 2019 study in dogs with adult-onset demodicosis found a confirmed concurrent disease, most often hyperglucocorticoidism or hypothyroidism, in around 40% of cases.
Cheyletiella (walking dandruff)
Cheyletiella mites are large enough to be seen with the naked eye as moving specks in the dandruff — hence the common name. They cause mild to moderate itch and scaling along the dorsal (back) surface. They can spread between dogs, cats, rabbits, and humans.
Treatment is usually straightforward with appropriate anti-parasitic products, applied to all animals in contact.
Lice
Lice in pets are species-specific — dog lice don't infest cats, and neither species affects people. They are visible to the naked eye, move slowly, and attach their eggs (nits) firmly to hair shafts.
Lice are most common in animals in crowded conditions, in neglected coats, or in very young or debilitated animals. Treatment involves appropriate insecticidal products and environmental cleaning, since lice survive off the host briefly.
Approaching Skin Infections and Parasites Systematically
When I see a pet with skin disease, my diagnostic approach follows a set sequence:
- Rule out parasites first — a skin scraping, tape prep, or response to empirical anti-parasitic treatment
- Assess for and treat secondary infection — cytology identifies bacteria and yeast
- Evaluate for underlying disease — allergy workup, hormonal testing where indicated
This sequence matters because treating a secondary infection without finding the underlying cause results in recurrence. The infection is the consequence; the underlying disease is the cause.
For a complete overview of keeping the skin barrier healthy overall, and for understanding the allergies that commonly underlie secondary infections, those articles provide the broader context this topic fits within.
Frequently Asked Questions
Can I treat my pet's skin infection at home?
Minor, very localized bacterial surface infections may improve with topical antibacterial products, but this should be confirmed with your vet first. Deep pyoderma, mange, and ringworm require prescription treatment and appropriate diagnosis. Treating with over-the-counter products without knowing what you're treating often delays proper care and can complicate diagnosis — some products mask signs without resolving the underlying condition.
How do I know if my pet has mange or just dry skin?
Dry skin usually causes generalized scaling without intense itch or hair loss. Mange — particularly sarcoptic mange — is associated with intense, relentless itch (often described as the worst itch an animal can experience) and progressive hair loss. Demodectic mange causes hair loss without much itch in most cases. If your pet is scratching intensely enough to cause self-trauma, see a vet rather than assuming dry skin.
Is ringworm dangerous?
In pets, ringworm is uncomfortable and requires treatment, but it's not dangerous to a healthy animal in the same way as a systemic infection. The concern is primarily contagion — to other pets and to humans, particularly children, elderly family members, and people who are immunocompromised. Affected pets should have limited contact with vulnerable individuals until treatment is confirmed effective.
My pet was treated for skin infection but it keeps coming back. Why?
Recurrence usually means the underlying cause wasn't addressed. The most common reason pyoderma and yeast infections recur is inadequately treated or undiagnosed allergy. If your pet's skin infections are recurring despite appropriate antibiotic treatment, an allergy workup is the next step. Resistant infections (MRSP) are another possibility and require culture and sensitivity testing.