Food allergy vs food intolerance

A food allergy involves an immune-system reaction, most often to a protein, whereas a food intolerance does not involve the immune system and stems, for example, from impaired digestion such as a difficulty handling lactose or fat. The two are often confused because their clinical signs can look similar, including digestive upset and sometimes skin problems, yet the underlying mechanisms differ (veterinary literature). The distinction matters for management. A genuine allergy is to a specific protein, so the most reliable way to identify it is a supervised [elimination diet](/glossary/elimination-diet) using a [single-protein](/glossary/single-protein) novel source such as [horse](/glossary/horse) or [venison](/glossary/venison-deer), or a [protein hydrolysate](/glossary/protein-hydrolysate), followed by reintroduction to confirm the trigger. Notably, the most commonly reported food allergens in dogs are everyday proteins such as [beef](/glossary/beef), dairy and chicken, precisely because they are eaten so often, not because they are inherently dangerous. An intolerance may instead improve simply by adjusting the offending ingredient or improving digestibility. The marker: allergy and intolerance are different problems that look alike, so a structured veterinary approach beats guessing, and self-directed diet-hopping rarely identifies the cause, a theme returned to throughout the [Petipedia glossary](/glossary).

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