SYMPTOM
Pustules or pimples on skin
Small raised bumps on the skin that may be white, yellow, or red, sometimes rupturing to leave crusts or circular lesions.
Bacterial Skin Infection (Pyoderma)
Pustules are a hallmark of bacterial skin infection, forming when neutrophils accumulate in response to bacterial invasion of the epidermis or hair follicles. Superficial pyoderma produces classic small pustules that may be surrounded by a ring of redness, often concentrated in the groin, axillae, and ventral abdomen. The pustules are typically fragile and may rupture quickly, leaving behind circular crusts or epidermal collarettes.
Allergic Dermatitis
While allergies themselves do not cause pustules directly, the skin barrier disruption, self-trauma from scratching, and secondary bacterial colonisation that accompanies allergic skin disease frequently leads to pustule formation. Atopic dermatitis and food allergy commonly produce a cycle where allergic inflammation compromises the skin barrier, allowing bacteria to invade and form pustules, which in turn provoke further itching and scratching.
Demodicosis
Demodectic mange, caused by Demodex mites living within hair follicles, can produce papules and pustules as the mites provoke follicular inflammation and secondary bacterial infection. The pustules in demodicosis often concentrate around the face, forelegs, and trunk in generalised forms, and may be accompanied by areas of hair loss and scaling.
Dermatophytosis (Ringworm)
Fungal skin infections can occasionally produce pustular lesions, though they more commonly present with circular areas of hair loss and scaling. When pustules do occur with dermatophyte infections, they may be accompanied by characteristic circular spreading patterns and broken hairs at the margins of the lesions.
Immune-Mediated Skin Disease
Conditions such as pemphigus foliaceus produce distinctive pustules that may be larger and more persistent than those of bacterial pyoderma. These autoimmune pustules often affect the face, ear pinnae, and footpads in characteristic distributions and contain acantholytic cells rather than the bacteria found in infectious pustules. Immune-mediated causes tend to be less responsive to antibiotic therapy alone.
Why timing matters
Early observation
When pustules first appear, they may be few in number, small, and easily overlooked, particularly in dogs with thick or dark coats. Early pustules may be most visible on the ventral abdomen, inner thighs, or other sparsely-haired areas where the skin is easily inspected. At this early stage, the dog may show minimal signs of discomfort, or may begin scratching or licking at the affected areas intermittently.
Later presentation
As the number and distribution of pustules increases, the condition becomes more visually obvious and may cause significant discomfort. Ruptured pustules leave behind crusting, scaling, and circular lesions that create a moth-eaten appearance to the coat. The skin may become increasingly reddened, and the dog may show more persistent scratching, licking, or rubbing. In cases that progress to deep infection, the lesions may become nodular, painful, and may produce draining tracts.
The trajectory of pustular skin disease depends on the underlying cause. Bacterial pyoderma may wax and wane with environmental conditions and the activity of any underlying allergic disease. Pustules from immune-mediated conditions tend to progress steadily without antibiotic response. Parasitic causes may follow seasonal patterns or progressive spread. Whether pustules respond to empirical antibiotic therapy, recur after treatment cessation, or fail to respond at all provides important diagnostic information about the underlying cause.
Conditions commonly associated
Pyoderma in Dogs
Pyoderma commonly produces pustules or pimple-like lesions on the skin surface, representing localised bacterial infection within hair follicles or superficial skin layers.
Atopic Dermatitis in Dogs
Atopic dermatitis disrupts the skin barrier and creates conditions favourable for secondary bacterial infection, which may manifest as pustules or papules.
Demodectic Mange
Pustules and papules commonly develop in demodectic mange when secondary bacterial infection involves the damaged hair follicles, creating a condition known as demodectic pyoderma.
Pyoderma
Pustules and pimples are characteristic early signs of bacterial skin infection, forming as bacteria multiply within hair follicles or skin layers.
When to explore further
Pustules that spread rapidly across the body, increase in number despite home care, or are accompanied by significant itching or discomfort may suggest an active infectious or inflammatory process that is unlikely to self-resolve.
Recurrent pustules that clear with treatment but return within weeks of stopping therapy often indicate an incompletely addressed underlying trigger such as allergic skin disease, hormonal imbalance, or persistent parasitic infestation.
Pustules that predominantly affect the face, ear tips, or footpads rather than the typical truncal distribution may suggest an immune-mediated condition rather than straightforward bacterial infection.
Large, deep, or painful pustules or nodules that drain bloody or purulent material suggest deep skin infection that differs in severity and management from simple superficial pustules.
Pustules appearing alongside other signs such as hair loss, darkening of the skin, increased thirst, or changes in body shape may suggest an underlying systemic condition contributing to impaired skin immunity.
Noting the distribution of pustules across the body, their size and character, whether they are itchy, and how they evolve over time can help build a picture of the underlying cause. Photographing affected areas at regular intervals provides a visual record that can track progression or improvement. Observing whether the dog is scratching or licking at the pustules, which areas seem most affected, and whether the lesions leave behind circular crusts or spreading redness all contribute to characterising the pattern.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS