Food allergies occur when a pet's immune system overreacts to intact protein molecules in ingredients like chicken, beef, or soy. Hydrolysis uses enzymes or acid to break proteins into peptides below the immune recognition threshold, typically under 10,000 daltons. Hydrolyzed protein diets are prescribed for elimination diet trials to diagnose food allergies and for long-term management of confirmed sensitivities. Common veterinary brands use hydrolyzed chicken, soy, or salmon. These diets are available only through veterinarians, cost more than standard food, and must be fed exclusively to be effective since even small treats with intact proteins can trigger reactions. They differ from limited-ingredient diets, which use novel proteins rather than broken-down ones.