Dog Skin Conditions: Rashes, Itching and What Causes Them

Reviewed by Dr. Jamshed Bilal, DVM

Skin and coat problems are among the most frequent reasons dogs are brought to the vet, and with good reason — a dog that is constantly scratching, licking, rubbing, and chewing at themselves is uncomfortable, and chronic skin disease can significantly affect quality of life. The challenge is that many different conditions produce similar-looking symptoms. Getting to the right diagnosis — and therefore the right treatment — requires looking at the whole picture: where the problem is, when it started, whether it is seasonal, and what has already been tried. This guide covers the most common causes and what distinguishes them.

The Most Common Causes of Skin Problems in Dogs

Before you can treat a skin problem, you need to understand which category it falls into. The main causes are allergies, parasites, bacterial infection, fungal infection, yeast overgrowth, hot spots, hormonal conditions, and seborrhoea — and importantly, more than one can be present at the same time.

Allergies: Environmental and Food

Allergic skin disease — in its environmental form called atopic dermatitis — is the most commonly diagnosed chronic skin condition in dogs. Environmental atopy is triggered by inhaled or contact allergens: pollen, dust mites, mould spores, and grass. It tends to affect the paws, ears, belly, armpits, groin, and face. Seasonal patterns (worsening in spring and summer) suggest pollen triggers; year-round symptoms suggest dust mites or mould.

Food allergy or food hypersensitivity produces a very similar pattern of skin symptoms — itchy paws, recurrent ear infections, facial rubbing — but may also include gastrointestinal signs such as vomiting, loose stools, and increased frequency of defecation. Crucially, food allergy symptoms are present year-round rather than seasonally, because the dog is being exposed to the food continuously. See our detailed guide to food versus environmental allergies for a full comparison.

Fleas and Flea Allergy Dermatitis

Fleas are the single most common external parasite cause of skin problems in dogs, and flea allergy dermatitis (FAD) is the most common allergic skin disease overall. A dog that is allergic to flea saliva does not need to be heavily infested — a single flea bite is enough to trigger a severe, prolonged allergic reaction in a sensitised dog.

FAD typically causes intense itching concentrated at the base of the tail, lower back, and inner thighs. The dog may scratch, bite, and lick these areas to the point of hair loss and self-trauma. You may not see fleas on the dog — they move quickly and a hypersensitive dog grooms them off obsessively — but the flea dirt test is reliable: comb the dog and place collected debris onto a damp white tissue. Flea dirt dissolves into reddish-brown streaks (from digested blood). If you see this, you have fleas.

Critically, treating only the dog is not enough. Up to 95% of a flea population lives in the environment — carpets, furniture, and bedding. Effective treatment requires treating all household pets (including cats) with a veterinary-strength flea product and treating the household environment with a long-acting household spray. Over-the-counter flea products are frequently ineffective; veterinary-prescription products (spot-ons, oral treatments) are far more reliable.

Mange: Sarcoptic and Demodectic

Mange refers to skin disease caused by mites, but the two main types are very different in their cause, presentation, and management.

Sarcoptic mange (scabies) is caused by the microscopic Sarcoptes scabiei mite, which burrows into the outer layers of skin and causes intense, frantic itching that is often described as unbearable. It typically begins at the ear margins, elbows, hocks, and belly, and spreads rapidly. It is highly contagious between dogs and can temporarily infect humans, causing a self-limiting itchy rash. Diagnosis can be tricky as mites are hard to find on skin scrapes; treatment response is often used as part of the diagnostic process. Treatment typically requires multiple doses of antiparasitic treatment and quarantine from other dogs during treatment.

Demodectic mange is caused by Demodex canis mites, which normally inhabit hair follicles in small numbers in all dogs without causing problems. Disease occurs when these mites overpopulate, typically in young dogs with an immature immune system or in any dog with a compromised immune system (from illness, medication, or genetics). Demodex does not cause the intense itch of sarcoptic mange — the primary signs are hair loss, often in circular patches, with variable redness and scaling. It is not contagious to other dogs or humans. Localised cases in young dogs frequently resolve without treatment; generalised cases require antiparasitic treatment and investigation for any underlying cause of immune suppression.

Bacterial Skin Infections (Pyoderma)

Pyoderma — bacterial infection of the skin — is extremely common in dogs and almost always occurs secondary to another problem that has disrupted the skin's normal barrier function. Allergic skin disease, parasites, wounds, skin folds (in brachycephalic and wrinkly breeds), and hormonal conditions can all predispose to pyoderma. The most common bacterial cause is Staphylococcus pseudintermedius.

Superficial pyoderma presents as small pustules, crusted spots, circular areas of hair loss with scaling (epidermal collarettes), and redness. Deep pyoderma is more serious — nodules, draining tracts, significant swelling, and pain. Both require veterinary treatment; superficial cases are typically treated with topical antibacterial shampoos and sometimes oral antibiotics, while deep infections require systemic treatment and culture and sensitivity testing to guide antibiotic choice.

Fungal Infections and Ringworm

Ringworm (dermatophytosis) is a fungal infection — not a worm — caused by dermatophyte fungi including Microsporum canis and Trichophyton mentagrophytes. In dogs, it typically presents as circular, scaly patches of hair loss, sometimes with mild redness. It is mildly itchy at most. Importantly, ringworm is zoonotic — it spreads between dogs, cats, and humans. Any household member showing a classic circular rash should see their GP. Treatment involves antifungal medication (topical and sometimes systemic) and environmental decontamination.

Yeast Infections (Malassezia Dermatitis)

The yeast Malassezia pachydermatis normally lives on dog skin in low numbers. Overgrowth occurs in warm, moist environments — skin folds, ear canals, between the toes, under the tail, and in the armpits — and in dogs with allergic skin disease whose skin barrier is compromised. The characteristic signs are intense itching, a distinctive musty or cheesy odour, reddish-brown discolouration of the coat (from licking), greasy or waxy skin texture, and thickened, darkened skin in chronic cases. Ears with yeast infections smell particularly strong and have dark, waxy debris. Treatment requires antifungal shampoo, wipes, or medication; but if the underlying cause (usually allergy) is not addressed, recurrence is the rule rather than the exception.

Hot Spots (Acute Moist Dermatitis)

A hot spot is a localised area of acutely inflamed, infected skin that appears, seemingly from nowhere, as a rapidly spreading moist, red, weeping lesion. Dogs lick and chew at the area obsessively, rapidly enlarging the lesion. They are commonly caused by moisture trapped against the skin (from swimming, bathing, or rain), combined with itching from any cause that starts the self-trauma cycle — flea bites, contact allergy, or boredom.

Hot spots are painful, spread fast, and need prompt treatment. First aid involves clipping the hair around and over the lesion, cleaning it gently, and preventing the dog from accessing it with a buster collar. Veterinary treatment typically includes topical or systemic antibiotics and anti-inflammatory medication. Identifying and addressing the underlying trigger prevents recurrence.

Hormonal Skin Conditions

Hypothyroidism (underactive thyroid) and hyperadrenocorticism (Cushing's disease) both cause skin changes in dogs. Hypothyroidism typically produces dry, flaky, thickened skin, bilateral symmetric hair loss on the flanks and trunk (not the head or legs), poor coat quality, and a "tragic expression" from facial skin changes. Cushing's disease produces a pot-bellied appearance, a thin coat with bilateral hair loss, a thinned and fragile skin with calcium deposits (calcinosis cutis), and increased susceptibility to skin infections. Both conditions are diagnosed through blood tests and managed medically rather than topically.

Seborrhoea

Seborrhoea is a condition of the skin's oil-producing glands, resulting in either dry, flaky skin (seborrhoea sicca) or greasy, odorous skin with thick scaling (seborrhoea oleosa). Primary seborrhoea is genetic and seen in specific breeds (Cocker Spaniels, West Highland White Terriers, Basset Hounds). Secondary seborrhoea is far more common and develops as a consequence of another underlying condition — allergy, hormonal disease, or infection. Treatment of secondary seborrhoea requires treating the primary cause; medicated shampoos help manage the symptoms.

What NOT to Use on Your Dog's Skin

Some well-intentioned home remedies cause real harm. Tea tree oil is toxic to dogs — it is absorbed through the skin and can cause neurological signs including ataxia, tremors, and depression, even in small amounts. Never apply undiluted tea tree oil to a dog, and avoid products containing it. Human topical steroid creams, antifungal preparations, and antiseptic products are formulated for human skin and may contain concentrations or ingredients that are harmful when a dog licks them off. If you are uncertain whether a product is safe, ask your vet before applying it.

When to See a Vet

Any skin problem that persists beyond a week, spreads, is causing significant distress, involves open or weeping lesions, has an unusual odour, or is accompanied by other symptoms (lethargy, changes in appetite or thirst, digestive changes) warrants a veterinary examination. Skin conditions that appear simple on the surface are often more complex underneath, and early accurate diagnosis leads to faster resolution and less suffering for your dog.

Frequently Asked Questions

Why is my dog so itchy?

The most common causes are allergies (food or environmental), fleas or flea allergy, yeast infection, and bacterial skin infection. Seasonal itching suggests environmental allergens; year-round itching points toward food allergy, dust mites, or yeast. A veterinary examination is needed to identify the specific cause.

What does a dog skin allergy look like?

Redness, persistent licking and chewing of the paws, recurring ear infections, rubbing the face, and hair loss from self-trauma in affected areas. The belly, groin, armpits, and paws are commonly affected. Secondary bacterial or yeast infections are very common on top of allergic skin disease.

Is ringworm in dogs contagious to humans?

Yes. Ringworm is a fungal infection and a zoonotic disease — it can spread between dogs, cats, and humans. All household members and pets should be monitored if your dog is diagnosed, and hygiene measures are essential during treatment.

What is the difference between sarcoptic and demodectic mange?

Sarcoptic mange (scabies) causes intense itching, is highly contagious to other dogs and can temporarily affect humans. Demodectic mange is not contagious, causes hair loss more than itching, and is related to immune system function. They require different treatments.

Can I use hydrocortisone cream on my dog?

Very low-strength hydrocortisone can be used cautiously for short-term relief on small, localised areas in places the dog cannot lick. For anything beyond minor, localised irritation — or symptoms persisting more than a few days — veterinary assessment is needed.

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Disclaimer: This article is for educational purposes only. Always consult your veterinarian before making significant changes to your dog's care or training routine.