Dog Skin Conditions: Identification, Symptoms, and Current Treatments

Canine Atopic Dermatitis (CAD)

Canine atopic dermatitis is a chronic, hereditary, inflammatory skin disease driven by an abnormal immune response to environmental allergens. A defect in the skin barrier allows allergens such as pollen, dust mites, mould spores, and animal dander to penetrate the skin, triggering an immune cascade that produces intense pruritus (itch), inflammation, and further skin barrier damage in a self-perpetuating cycle. It is estimated to affect 10 to 15 percent of the dog population and is the most common form of allergic skin disease seen in veterinary practice. See our guide on managing pet allergies for household and environmental control strategies.

Atopic dermatitis typically presents between six months and three years of age, and the first signs are often seasonal before becoming year-round as sensitisation expands. Common symptoms include intense scratching, face rubbing, and licking of the paws, groin, armpits, and ears. Chronic cases show thickened, darkened, lichenified skin in these zones and recurrent ear and skin infections from secondary bacterial and yeast overgrowth.

Flea Allergy Dermatitis

Flea allergy dermatitis is the most common allergic skin disease in dogs worldwide. It is not simply a reaction to flea bites; it is a hypersensitivity reaction to proteins in flea saliva. A single flea bite can trigger intense, prolonged itching in a sensitised dog. The characteristic distribution is over the rump, base of tail, inner thighs, and abdomen, a pattern sometimes called "hot pants distribution." Hair loss over the rump and base of the tail with visible skin thickening and secondary infection is classic FAD.

Critically, dogs with FAD may have very few visible fleas because they groom compulsively. Finding a flea or flea dirt (small dark comma-shaped specks that dissolve red on a wet tissue) anywhere on the dog is sufficient to diagnose FAD in a pruritic dog. Year-round veterinarian-prescribed flea prevention on all pets in the household and in the home environment is the cornerstone of management.

Cutaneous Adverse Food Reaction (Food Allergy)

Cutaneous adverse food reactions cause skin symptoms clinically indistinguishable from environmental atopic dermatitis. The most common food allergens in dogs are proteins they have been exposed to over a long period, particularly beef, chicken, dairy products, wheat, and egg. Contrary to popular belief, food allergies are not typically triggered by new foods but by proteins the dog has eaten repeatedly over months to years.

The only validated way to diagnose a food allergy is a strict dietary elimination trial using a novel protein and novel carbohydrate diet (ingredients the dog has never eaten before) or a hydrolysed protein prescription diet for a minimum of 8 to 12 weeks. Blood and skin prick allergy tests for food do not reliably diagnose canine food allergies and should not be used as a substitute for a properly conducted elimination trial. During the trial, the dog must eat nothing except the trial diet, including treats and flavoured medications.

Hot Spots (Acute Moist Dermatitis)

Hot spots are rapidly developing, intensely painful and itchy lesions that appear as moist, red, weeping, matted patches of skin. They develop when a dog scratches, licks, or chews a specific area repeatedly, breaking the skin surface and allowing bacteria to colonise the warm, moist environment. The result is a rapidly worsening cycle of itch, self-trauma, and infection that can expand significantly within hours. Hot spots are most common in dense-coated breeds including Golden Retrievers, German Shepherds, and Saint Bernards, and are more frequent in hot, humid weather.

Treatment involves clipping and cleaning the affected area, topical or systemic antibiotics, corticosteroids to break the itch cycle, and an E-collar to prevent further self-trauma. The underlying trigger must also be identified and addressed: flea allergy, ear infection, matted fur, and contact allergy are common precipitants. Without addressing the trigger, hot spots recur.

Bacterial Pyoderma

Pyoderma literally means pus in the skin. It is a bacterial skin infection, most commonly caused by Staphylococcus pseudintermedius, a bacterium that normally lives on dog skin in small numbers but overgrows when the skin barrier is compromised by allergies, trauma, moisture, or immune suppression. Surface pyoderma (hot spots, skin fold infections) affects the surface layers. Superficial pyoderma is the most common form, presenting as folliculitis with small pus-filled bumps (pustules), crusted lesions, and circular patches of hair loss. Deep pyoderma, which penetrates below the dermis, is more serious and typically requires systemic antibiotics for four to eight weeks.

The critical point about pyoderma is that it is almost always secondary to an underlying condition. Treating the infection without identifying and managing the underlying cause invariably results in rapid recurrence. The most common underlying causes are atopic dermatitis, flea allergy, food allergy, hormonal disease (hypothyroidism, hyperadrenocorticism), and immune suppression. Antibiotic resistance is an increasing concern in recurrent pyoderma cases; culture and sensitivity testing guides antibiotic selection in dogs with a history of recurrence.

Malassezia Dermatitis (Yeast)

Malassezia pachydermatis is a yeast that normally inhabits dog skin in low numbers. It overgrows when skin conditions become favourable: increased moisture, elevated oil production (sebum), disruption of the normal skin barrier, or immune compromise. In allergic dogs, Malassezia is an extremely common secondary complication and significantly worsens the pruritus associated with the primary allergic disease, often to the point where the secondary yeast infection is responsible for much of the itch experienced.

Classic Malassezia dermatitis has a distinctive appearance and smell. The affected skin is greasy, reddened, and thickened, with a notable musty, yeasty, or "corn chip" odour that many owners describe immediately. Common locations include the ears, paws (particularly between the toes), skin folds, armpits, groin, and around the neck. The skin may show brown discolouration from chronic inflammation and appear lichenified. Treatment involves topical antifungal shampoos and wipes (typically containing chlorhexidine and miconazole or ketoconazole) and oral antifungal medication for more clear cases.

Sarcoptic Mange (Scabies)

Sarcoptic mange is caused by the mite Sarcoptes scabiei burrowing into the outer layers of the skin. It is intensely, almost unbearably itchy and highly contagious to other dogs and temporarily to humans. The ear margins, elbows, hocks, and ventral abdomen are commonly affected first. Dogs with sarcoptic mange appear desperate in their scratching, and the condition can rapidly cause widespread hair loss, skin thickening, crusting, and secondary infections across the entire body if untreated. The "pedal pinna reflex," where scratching the ear margin causes the hind leg to scratch reflexively, is a useful clinical sign. Diagnosis is confirmed by skin scraping, though mites can be difficult to find; a positive treatment response to anti-mite medication is often diagnostic.

Demodectic Mange (Demodicosis)

Demodectic mange is caused by an overgrowth of Demodex canis mites that normally live in small numbers in the hair follicles of all dogs. It is not contagious between dogs and does not infect humans. Demodicosis typically occurs in puppies and young dogs with immature immune systems or in older dogs with underlying immune suppression. Localised demodicosis (a few patches of hair loss, usually on the face) often resolves spontaneously in puppies as the immune system matures. Generalised demodicosis requires treatment and investigation for an underlying immunosuppressive condition in adult dogs.

Ringworm (Dermatophytosis)

Despite its name, ringworm is not a worm. It is a fungal infection of the skin, hair, and nails caused by dermatophyte fungi, most commonly Microsporum canis in dogs. It is highly contagious to other animals and to humans, making prompt diagnosis and treatment important from a public health standpoint. In dogs it presents as circular or irregular patches of hair loss with mild scaling or redness. The classic "ring" appearance with a clear centre and inflamed border, well-known in human ringworm, is less consistently seen in dogs. Diagnosis is by Wood's lamp examination (Microsporum canis fluoresces apple-green, though not all strains fluoresce), fungal culture, or PCR testing.

Seborrhea

Seborrhea is a disorder of skin cell turnover and sebaceous gland function that results in a greasy, flaky, or scaly coat with an unpleasant odour. It exists in two forms: dry seborrhea (seborrhea sicca) with flaky, dandruff-like scaling, and oily seborrhea (seborrhea oleosa) with excessive greasiness and a rancid smell. Primary seborrhea is rare and inherited, occurring in specific breeds including American Cocker Spaniels, West Highland Terriers, Basset Hounds, and Labrador Retrievers. Secondary seborrhea is far more common and results from an underlying condition such as allergic disease, hypothyroidism, Cushing's disease, or deficiency in essential fatty acids. Identifying and treating the underlying cause is the most important step in managing secondary seborrhea.