True food allergies are an immune response to a specific protein molecule, distinct from food intolerance (digestive upset without immune involvement). Estimated to affect under 10% of dogs and cats with skin or GI complaints. The most common food allergens in dogs are beef, chicken, dairy, and wheat — chicken (the dominant protein in pet food) is a more common trigger than corn or grain. Diagnosis is by elimination diet using a novel or hydrolyzed protein for 8–12 weeks; blood, saliva, and hair tests are not validated and produce false positives. Grain-free is not an evidence-based response to most dietary issues.