CONDITION
Pyoderma
Pyoderma describes bacterial infection of the skin. It develops when bacteria (most often those that live harmlessly on the surface in healthy animals) multiply within the layers of the skin itself, triggering inflammation and damage. The infection can be confined to the very surface, or it can extend deeper into the tissue. Owners often notice redness, small raised bumps, crusting, or circular patches where the hair has thinned or fallen away. Some dogs develop a distinctive smell, or the skin may feel warm or thickened in affected areas. Itching is common, though not always present. The pattern and extent can vary widely, from a few isolated spots to large areas of the body. This page explores what pyoderma can look like in different forms, what tends to lie beneath it (including factors that allow bacteria to take hold) and how it is investigated and approached. The aim is to help you understand what may be happening when skin infection is part of the picture.
Why this matters now
Bacterial skin infections can develop at any age, though they often emerge secondary to underlying conditions such as allergies, hormonal imbalances, or skin trauma. Warm, moist areas of skin, such as skin folds, tend to carry higher bacterial counts and are at greater risk of infection.
Initial superficial infections may present as small pustules or areas of redness that can spread if the underlying trigger persists. Without addressing root causes, infections often recur or deepen into the dermis, potentially forming painful nodules, draining tracts, or widespread crusting that becomes increasingly difficult to resolve.
Signals & patterns
Early signals
Small pustules or pimples on the skin
Early bacterial infection often appears as raised bumps with white or yellow centres, particularly on the belly, inner thighs, or areas with less hair coverage.
Red, inflamed patches
Areas of skin may appear flushed or irritated, often forming a ring-shaped lesion known as an epidermal collarette: a scaling or peeling rim surrounding a healing centre, and a typical lesion of superficial pyoderma in dogs. These can appear singly or in clusters, particularly on the trunk and inner thighs.
Mild itching or licking
Dogs may pay increased attention to affected areas, though scratching intensity can vary depending on the level of discomfort.
Patchy hair loss
Infected areas may show thinning coat or circular bald spots where hair has fallen out or been damaged by the inflammatory process.
Later signals
Crusting and scab formation
As pustules rupture and dry, yellowish-brown crusts often develop over the affected skin.
Spreading areas of infection
Multiple patches may coalesce or new areas appear as bacteria spread across the skin surface.
Deep nodules or draining wounds
Severe infections can penetrate deeper skin layers, forming painful lumps that may rupture and discharge purulent material.
Unpleasant skin odour
Bacterial overgrowth often produces a distinctive smell that becomes more noticeable as infection worsens.
Systemic signs of illness
Deep pyoderma can be accompanied by signs beyond the skin itself, including a raised temperature, dullness or reduced energy, reduced appetite, and enlargement of the lymph nodes near the affected area, reflecting a more extensive infection.
Click to read about the biological mechanisms
How this is usually investigated
Diagnosis typically involves visual examination of the skin lesions along with tests to identify the bacteria involved and investigate potential underlying causes.
Skin cytology
Bacterial culture and sensitivity
Skin scraping or hair pluck
Allergy testing or dietary trials
Hormonal evaluation
Options & trade-offs
Treatment focuses on eliminating the active infection while identifying and managing any underlying conditions that predispose to bacterial overgrowth.
Topical antimicrobial therapy
Medicated shampoos, sprays, wipes, or mousses containing antibacterial agents can be used alone for surface and superficial infections and alongside systemic treatment for deep infections.
Trade-offs: Requires regular application and bathing compliance. Not enough alone for deep infections, where current guidance always calls for systemic antibiotics as well.
Systemic antibiotics
Oral or injectable antibiotics treat bacteria from within, reaching deeper tissues and providing broader coverage.
Trade-offs: Current stewardship guidance favours topical treatment alone for surface and superficial infections where an owner can manage regular application, reserving systemic antibiotics for deep infections or superficial cases that do not respond adequately to topical treatment. Courses run for weeks: current guidance gives an initial 2 weeks for superficial and 3 weeks for deep infections, each followed by re-examination, and finds no evidence to support continuing a systemic antibiotic beyond the resolution of clinical signs. Because antibiotic-resistant staphylococci such as MRSP are increasingly recognised in recurrent or non-healing infections, current guidance recommends culture and sensitivity testing whenever a systemic antibiotic is planned, and most strongly for deep infections, recurrent infections, and dogs given more than one course of systemic antibiotics in the past 6 months.
Addressing underlying conditions
Managing allergies, hormonal disorders, or parasites that compromise skin health reduces the likelihood of recurring infections.
Trade-offs: Needed for long-term control but may require ongoing management. Some underlying conditions cannot be cured, only controlled.
Immune-modulating approaches
For dogs with recurrent infections where no underlying trigger can be identified or fully controlled, a course of autogenous bacterin (a vaccine prepared from bacteria cultured from the individual dog's own skin) is sometimes used alongside, or as an alternative to, repeated courses of antibiotics, with the aim of reducing how often and how severely flares occur.
Trade-offs: Evidence comes from a small number of studies, and response varies between individuals: some dogs show a meaningful reduction in flare frequency and antibiotic use, whilst others show little change. Preparation takes time, since bacteria must first be cultured from an active lesion, and a course of injections is usually needed before any benefit becomes apparent. Autogenous bacterins hold no UK marketing authorisation: each is an inactivated vaccine made to order by a laboratory holding an Autogenous Vaccine Authorisation from the Veterinary Medicines Directorate, and published guidance notes that availability is very limited in many countries.
Common misconceptions
"Skin infections are contagious to other pets or people"
Most pyoderma develops from bacteria already present on the dog's own skin when conditions allow overgrowth, rather than from a new organism introduced by another animal or person. Some strains, including meticillin-resistant Staphylococcus pseudintermedius (MRSP), can pass through close contact to other pets in the household and, less often, to the people the dog lives with, and matching strains have been found in affected dogs, their in-contact pets and the home environment. Spread to people appears to be uncommon and rarely causes illness in otherwise healthy people, though those who are immunocompromised are at greater risk of infection from these bacteria, and simple hygiene measures such as handwashing after contact with affected skin remain a reasonable precaution.
"A short course of antibiotics will permanently resolve the problem"
If underlying triggers such as allergies or hormonal conditions remain unaddressed, infections often recur once treatment stops. Identifying and managing root causes tends to be needed for lasting improvement.
"Pyoderma indicates poor hygiene or neglect"
Skin infections can affect well-cared-for dogs and often reflect underlying health issues rather than cleanliness. Some breeds have conformational features that predispose them regardless of care quality.
Related conditions
Atopic Dermatitis in Dogs
Atopic dermatitis often creates conditions that allow pyoderma to develop. The damaged, inflamed skin barrier and persistent scratching in allergic dogs can permit surface bacteria to invade deeper layers, and many dogs with atopy experience recurring episodes of secondary bacterial skin infection.
Otitis Externa in Dogs
Otitis externa and pyoderma can share underlying causes, particularly allergic skin disease and disturbances in the skin's normal microbial balance. Dogs with atopic dermatitis may develop bacterial infection in both the ear canals and other areas of the body, and the same bacteria are often involved in both sites.
Cushings Disease in Dogs
Cushing's disease can predispose dogs to pyoderma. Excess cortisol weakens the skin's immune defences and alters its structure, making it easier for bacteria to colonise and multiply, and skin infections in dogs with Cushing's may be slower to resolve or recur more readily.
Hypothyroidism in Dogs
Hypothyroidism can contribute to skin changes that favour bacterial infection. The coat may become dull and thin, the skin thickened or oily, and the normal turnover of surface cells may slow, creating an environment in which bacteria can establish themselves more easily.
Sebaceous Adenitis
Sebaceous adenitis and pyoderma both involve disruption of the skin's normal architecture and barrier function, though through different mechanisms. Dogs with sebaceous adenitis may develop secondary bacterial infection as the loss of sebaceous glands alters the skin's protective oils and allows bacteria to take hold in areas of scaling or inflammation.
Dogs with skin lesions suggesting bacterial infection may benefit from examination to confirm the diagnosis and assess whether underlying conditions might be contributing. Recurrent infections particularly warrant investigation into allergies, hormonal status, or immune function to help prevent repeated cycles of infection and treatment.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS