Just like humans, some dogs can develop allergies to one or more ingredients (usually a protein source) in their regular diet. The onset of the first symptoms is typically sudden, meaning dogs can unexpectedly become allergic to something they’ve always eaten without any apparent problems. This is why pet owners are often surprised or even incredulous when a veterinarian diagnoses their dog with an allergy to a food ingredient that had never caused any issues before. However, along with a genetic predisposition, the key factor in the development of dog food allergies is simply prior exposure to the allergenic food. In other words, genetically predisposed dogs can only develop an allergy to a particular food ingredient if they’ve already eaten it at least once in their lifetime.
How Dog Food Allergies Develop
So, how do dog allergies to food develop? Food allergies in dogs are an immunologically mediated condition that occurs as a hypersensitivity reaction to a specific protein (called a “food allergen”) in the dog’s food. When a sensitive dog eats this food for the first time, its immune system responds by producing specific antibodies called immunoglobulins E (IgE) against the food allergen. However, this initial exposure typically doesn’t result in any visible adverse reactions. This process is called “sensitization.” Once sensitized, the dog’s immune system reacts more aggressively to subsequent exposures, producing more allergen-specific antibodies. These antibodies then stimulate certain cells to release histamine, the substance responsible for triggering allergic symptoms.
The proteins that can trigger allergic reactions in dogs may be from animal sources (e.g., beef, poultry, fish, eggs, milk, and their derivatives) or plant sources (e.g., legumes, soy, wheat, maize, and rice).
In sensitive dogs, allergic symptoms usually affect the skin and/or gastrointestinal system. Skin symptoms include itching, excessive licking or chewing, localized hair loss, various types of dermatitis, and even otitis (ear inflammation). Gastrointestinal symptoms—whether they occur with skin symptoms or on their own—typically include diarrhea, and occasionally vomiting and lack of appetite. Fortunately, anaphylaxis, the most severe allergic reaction, is rare in dogs.
It’s important to note that true food allergies in dogs are less common than many people think. Often, what seems like a food allergy is actually a food intolerance. Although food allergies and food intolerances have similar symptoms and are often confused, they are caused by different mechanisms. Food intolerance does not involve the immune system and is not an immunologically mediated disease. Instead, it often arises from inflammatory reactions to food additives (such as colorants, flavorings, antioxidants, and preservatives) or pharmacological substances naturally found in some foods (e.g., salicylate or histamine intolerance). Despite these differences, food allergies and intolerances share similar symptoms, and both require the same diagnostic and therapeutic approach.
Diagnosing Allergies in Dogs
Diagnosing both food allergies and food intolerances in dogs is not straightforward for at least two reasons. First, most dog foods, particularly commercial brands, contain multiple ingredients. Even in small quantities, any of these could act as an allergen or trigger food intolerance, making it difficult to pinpoint the exact cause of the symptoms. Second, a simple blood test is not sufficient to diagnose food allergies or intolerances in dogs, requiring a more complex approach.
The diagnosis of food allergies or intolerances is typically based on the dog’s response to a hypoallergenic diet. This diet can either be commercially prepared (with protein sources known to be unlikely to trigger allergies) or homemade (formulated with ingredients the dog has never eaten before). This approach, known as the “elimination diet method,” involves feeding the dog the hypoallergenic diet for 6 to 8 weeks. If no adverse reactions occur during this period, a diagnosis of food allergy or intolerance is likely. On the other hand, if the dog continues to show symptoms, it suggests that food allergies or intolerances may not be the issue, and further investigation is required to identify the true cause of the symptoms.
Once a diagnosis is made, it’s necessary to gradually reintroduce potential allergens into the dog’s diet, one at a time. If symptoms reappear after introducing a specific food, that ingredient is identified as the allergen or irritant.
Although diagnosing food allergies and intolerances in dogs can be challenging, both conditions can be effectively managed with the simplest approach: avoiding the problematic food!
