Why is my dog itchy?

Understanding Canine Pruritus: Common Causes of Itching in Dogs

Persistent itching, medically known as pruritus, is one of the most common reasons pet owners seek veterinary consultation. While an occasional scratch is normal, chronic pruritus can significantly impact a dog's quality of life, leading to skin lesions, infections, and behavioural changes. As veterinarians, our approach is to systematically investigate the underlying cause to provide effective and lasting relief.

Parasitic Infestations: Microscopic and Macroscopic Culprits

Parasites remain a critical consideration in any pruritic work-up, regardless of an animal's indoor or outdoor lifestyle.

• Flea Allergy Dermatitis (FAD): Even a single flea bite can trigger an intense, generalized allergic reaction in sensitized dogs due leading to severe pruritus, especially over the lumbosacral region, tail base, and inner thighs. Consistent, year-round flea prevention is paramount for control.

• Mites: Microscopic mites cause various forms of mange. Sarcoptes scabiei (sarcoptic mange) results in intensely itchy lesions, often on the ears, elbows, and hocks. Demodex canis (demodectic mange) can cause hair loss and skin inflammation, with variable pruritus. Both require specific diagnostic tests and treatment protocols.

Allergic Dermatitis: A Primary Driver of Pruritus

Allergies are a leading cause of canine pruritus. These hypersensitivity reactions manifest primarily as skin inflammation and itching.

• Environmental Allergies (Atopic Dermatitis): This is arguably the most prevalent form of canine allergy. Dogs can develop sensitivities to common environmental allergens such as pollens (from grasses, trees, weeds), dust mites, and mould spores. Clinical signs often include generalized itching, particularly affecting the paws, axillae (armpits), groin, and ears. The presentation can be seasonal or perennial depending on the allergen's presence. Genetic predisposition plays a significant role, with certain breeds showing a higher incidence of atopic dermatitis.

• Food Allergies: While frequently suspected by owners, food allergies constitute a smaller percentage of canine allergies (approximately 10%). Symptoms can mimic environmental allergies, presenting as non-seasonal pruritus, often accompanied by gastrointestinal signs like vomiting or diarrhoea. Diagnosis typically involves a strict elimination diet trial under veterinary supervision.

Secondary Infections: Complicating the Pruritic Picture

The integrity of the skin barrier is often compromised by primary allergic or parasitic conditions. This breach creates an opportunistic environment for secondary infections, which significantly exacerbate pruritus and skin pathology.

• Bacterial Pyoderma: Staphylococcus pseudintermedius is a common bacterial culprit, leading to pustules, crusts, epidermal collarettes, and further intense itching.

• Malassezia Dermatitis: An overgrowth of the yeast Malassezia pachydermatis can cause greasy, erythematous, and intensely pruritic skin, often with a characteristic odour. Treatment of these secondary infections is essential for breaking the itch-scratch cycle and allowing primary conditions to be managed effectively.

Other Potential Contributors

While less common, other factors can also contribute to pruritus:

• Dry Skin (Ichthyosis): Particularly in arid climates or during certain seasons, insufficient skin hydration can lead to flakiness and mild pruritus.

• Endocrine Disorders: Conditions such as hypothyroidism or Cushing's disease can manifest with various dermatological signs, including changes in coat quality and sometimes mild itching.

• Psychogenic Pruritus: In some cases, excessive licking or chewing may stem from behavioural issues or anxiety, leading to self-induced skin trauma and secondary infection.

Diagnosis and Management

A comprehensive veterinary examination, including a detailed history, is fundamental to diagnosing the cause of pruritus. Diagnostic tools may include skin scrapes, cytology, fungal cultures, blood tests, and allergy testing. Once a definitive diagnosis is established, a tailored treatment plan, often involving a multi-modal approach combining medical management with environmental controls, can be implemented to provide optimal relief and improve the dog's quality of life. Owners are encouraged to seek veterinary advice promptly for persistent itching to prevent the progression of skin disease and discomfort.