Bacterial skin infection in dogs — called pyoderma — is caused by overgrowth of bacteria (most commonly Staphylococcus pseudintermedius) in the skin. It produces red bumps, crusting, hair loss, and an unpleasant odour. Treatment involves antibiotics (oral or topical) and medicated shampoos. Most cases resolve within 3–6 weeks with the correct antibiotic, chosen based on skin cytology or culture results.

Bacterial skin infection — known medically as pyoderma — is one of the most common skin conditions in dogs and one of the top four reasons veterinarians prescribe antibiotics. It can develop as a primary problem, but more often it develops on top of another skin issue: allergies, mange, a hormonal condition, or a wound. Knowing what pyoderma looks like, how deep it goes, and what treatment is needed can make the difference between a 3-week recovery and months of recurring infections.

What Causes Bacterial Skin Infection in Dogs?

The bacteria responsible for most canine pyoderma are Staphylococcus pseudintermedius — a species that normally lives on a dog’s skin in small numbers without causing problems. Infection occurs when the skin’s natural defenses are compromised. Common triggers include:

• Allergies (environmental or food) — the most common underlying cause. Chronic inflammation disrupts the skin barrier
• Parasites — flea infestations, mange mites, and other ectoparasites damage the skin and allow bacteria to invade
• Hormonal disease — hypothyroidism and Cushing’s disease weaken immune function and skin integrity
• Skin folds — in breeds like Bulldogs, Pugs, and Shar Peis, warm and moist skin folds are a breeding ground for bacteria
• Wounds or trauma — cuts, abrasions, or post-surgical sites can become infected
• Immune suppression — dogs on long-term steroids or with immune disease are more susceptible

Types of Pyoderma — Superficial vs. Deep

Pyoderma is classified by how deep the infection penetrates into the skin. The depth determines how long treatment needs to run.

Signs and Symptoms of Bacterial Skin Infection in Dogs

Pyoderma can look different depending on depth and location. The most common signs include:

• Red pimples or pustules — small raised bumps filled with pus, often found on the belly or groin
• Circular scaly patches — epidermal collarettes — ring-shaped lesions with a crusty edge and clear centre
• Moth-eaten coat — patchy, irregular hair loss across the body that makes the coat look eaten away
• Crusting and scaling — yellow or brown crust on the skin surface
• Odour — a characteristic musty or yeasty-sour smell that worsens if untreated
• Redness and swelling — particularly in deep pyoderma between the toes or in skin folds
• Draining tracts — in severe deep pyoderma, infected tunnels in the skin may ooze fluid

Dogs with pyoderma are often itchy, though the degree of itching varies. Secondary yeast infections (Malassezia) frequently accompany bacterial pyoderma — a vet skin cytology swab distinguishes between the two and guides treatment.

How Vets Diagnose Pyoderma

Diagnosis begins with a physical examination — looking at the type, depth, and distribution of skin lesions. Your vet will typically perform:

• Skin cytology (impression smear): A swab or tape is pressed against a lesion and examined under a microscope. This identifies bacteria, yeast, and inflammatory cells quickly in the clinic.
• Skin culture and sensitivity: A sample is sent to a lab to identify the exact bacterial species and which antibiotics it responds to. Essential for recurrent or deep infections.
• Skin scraping: Rules out mange mites as an underlying cause
• Blood tests: If hormonal disease or immune suppression is suspected as the root cause

Treating without a cytology is common for first-time mild infections. But for recurrent pyoderma, culture and sensitivity results are essential — antibiotic resistance in Staphylococcus is a growing concern in veterinary medicine.

Vet-Recommended Treatment for Bacterial Skin Infection

Oral Antibiotics

Systemic antibiotics are the standard treatment for superficial and deep pyoderma. The antibiotic is chosen based on culture sensitivity results where available. First-line options commonly used in dogs include cephalexin and lincomycin-class antibiotics.

Topical Treatment and Medicated Shampoos

Topical therapy is used alongside oral antibiotics or as the sole treatment for mild surface pyoderma. It reduces the bacterial load on the skin surface and speeds healing.

• Medicated shampoos containing chlorhexidine or benzoyl peroxide — used 2–3 times per week
• Topical ointments for localised lesions — particularly useful for skin fold infections and small wound-site infections
• Ear flushes if concurrent ear infection (otitis externa) is present

Treating the Underlying Cause

Pyoderma that keeps coming back — recurring every few weeks or months — almost always has an underlying cause that hasn’t been addressed. The most common are allergies, flea infestation, and hormonal disease. Without treating the root problem, the infection will return regardless of how many courses of antibiotics are used.

How Long Does It Take to Clear Pyoderma?

A critical rule: always complete the full course of antibiotics even if the skin looks better. Stopping early allows resistant bacteria to survive and leads to harder-to-treat recurrent infections.

Frequently Asked Questions — Bacterial Skin Infection in Dogs

Q: What does bacterial skin infection look like on a dog?

A: Pyoderma typically shows as red pimples, circular crusty ring-shaped patches, patchy hair loss, and a musty odour. The belly and groin are common sites in mild infections. Severe cases may show swelling, oozing, or draining tracts, particularly between the toes.

Q: How do I know if my dog has pyoderma or just allergies?

A: Both cause itching and hair loss, which makes them hard to tell apart visually. Pyoderma specifically produces pimples, pustules, and crusting, while allergies typically cause diffuse redness and itching without obvious pus or lesions. Many dogs have both simultaneously — a skin cytology swab at your vet clinic can identify bacteria within minutes.

Q: Can pyoderma in dogs spread to humans?

A: Canine pyoderma is primarily caused by Staphylococcus pseudintermedius, which rarely infects humans. Standard hygiene precautions — washing hands after handling an infected dog — are sufficient. However, immunocompromised people should be more cautious and should speak with their doctor.

Q: What antibiotic is most commonly used for dog skin infections?

A: Cephalexin is the most widely used first-line antibiotic for canine pyoderma. It is effective against most Staphylococcal strains and is used at a dose of approximately 22 mg/kg twice daily for 3–6 weeks. Culture and sensitivity testing guides antibiotic choice in recurrent or non-responsive cases.

Q: Why does my dog keep getting skin infections?

A: Recurring pyoderma almost always indicates an unresolved underlying cause — most commonly atopic dermatitis (environmental allergies), food allergy, or flea allergy. Hormonal diseases like hypothyroidism or Cushing’s disease are also common culprits. A full diagnostic workup is needed to identify and address the root cause.

Q: Can I use human antibiotic cream on my dog’s skin infection?

A: No. Human topical antibiotics may contain ingredients harmful to dogs if licked, and they may not be effective against the bacteria causing canine pyoderma. Use only veterinary-formulated topical products. If your dog needs topical antibiotic treatment, your vet will prescribe the appropriate product.

Q: Is pyoderma contagious between dogs?

A: Pyoderma itself is not directly contagious. The bacteria involved are species that naturally live on dog skin. However, the underlying triggers — like mange mites or flea infestations — can spread between dogs. If you have multiple dogs and one develops pyoderma, check all pets for parasites.