What are the causes of skin allergies in dogs?

Itching, scratching, and recurring skin problems are among the most common reasons dogs end up at the vet. In many cases the underlying cause is an allergy. There are three main types: flea allergy dermatitis, food allergy, and environmental (atopic) allergy. Each has a distinct trigger and a different approach to diagnosis and management. Getting the right diagnosis matters because treating a food allergy with a flea protocol, or vice versa, will not help.

Flea allergy dermatitis

Flea allergy dermatitis (FAD) is one of the most common allergic skin diseases in dogs in regions where fleas are prevalent. [1] The reaction is not to the flea itself but to proteins in flea saliva. A single bite is enough to trigger a widespread inflammatory response in a sensitised dog.

Symptoms include intense itching, particularly at the base of the tail and hindquarters, along with hair loss, reddened skin, and bite marks from self-trauma. Highly allergic dogs are often so efficient at removing fleas by biting and scratching that you may not find any fleas on the dog itself, yet the reaction continues from occasional bites. A fine-toothed flea comb and checking bedding for flea dirt (small black specks that turn red when wet) can help confirm the suspicion.

The only effective management is comprehensive flea control: treating the dog with a vet-recommended product, treating all household pets, and treating the home environment. Flea pupae can survive in carpets and soft furnishings for months, so environmental treatment is not optional. [1]

Food allergy

Food allergy in dogs is triggered by an immune response to a specific protein in the diet. A 2016 systematic review that analysed data from 297 dogs found the most frequently reported allergens were beef (34%), dairy (17%), chicken (15%), wheat (13%), and lamb (14%). [2] Symptoms overlap with other allergies: persistent itching, recurring ear infections, and skin inflammation, typically in a non-seasonal pattern.

Diagnosis requires an elimination diet trial. This means feeding a novel or hydrolysed protein diet, one the dog has never been exposed to, exclusively for 8 to 12 weeks, with strict avoidance of everything else including flavoured medications and dental chews. [1] If symptoms resolve and then return when the original diet is reintroduced, the diagnosis is confirmed.

Novel protein sources with a low allergy risk include insect protein and plant-based protein, both absent from most standard dog diets. IMBY's insect-based and plant-based formulas contain no beef, dairy, chicken, lamb, or wheat.

Environmental (atopic) allergy

Atopic dermatitis is the most common allergic skin disease in dogs overall, affecting an estimated 10% of the dog population. [3] It is an inherited predisposition to develop allergic reactions to environmental substances: pollen, house dust mites, mould spores, and similar airborne or contact allergens.

Unlike flea or food allergy, atopy is typically seasonal at first, worse in spring and summer when pollen counts are high, but can become year-round as sensitisation broadens. Symptoms tend to concentrate on the face, paws, underside, and ears.

Diagnosis is made by ruling out flea allergy and food allergy first, then confirming with intradermal skin testing or serum allergy testing. Management options include allergen-specific immunotherapy (a long-term desensitisation programme), anti-itch medications, and topical treatments to support skin barrier function.

When to see the vet urgently

If your dog is scratching constantly, has open wounds from self-trauma, or shows signs of secondary bacterial infection (hot, moist, smelly skin lesions), book a vet appointment without delay. Allergies rarely self-resolve, and bacterial or yeast infections that develop on top of the primary allergy make things considerably worse if left untreated.